diff --git a/packages/ai-bot/tests/prompt-construction-test.ts b/packages/ai-bot/tests/prompt-construction-test.ts
index 59b084a9229..41c680cb26e 100644
--- a/packages/ai-bot/tests/prompt-construction-test.ts
+++ b/packages/ai-bot/tests/prompt-construction-test.ts
@@ -233,7 +233,7 @@ Current date and time: 2025-06-11T11:43:00.533Z
                   },
                   {
                     codeRef: {
-                      module: rri('https://cardstack.com/base/card-api'),
+                      module: rri('@cardstack/base/card-api'),
                       name: 'CardDef',
                     },
                     fields: [],
@@ -292,7 +292,7 @@ File open in code editor: http://localhost:4201/experiments/author.gts
   Inheritance chain:
     1. Address from http://localhost:4201/experiments/author
        Fields: street, city, state
-      2. CardDef from https://cardstack.com/base/card-api
+      2. CardDef from @cardstack/base/card-api
   Selected text: lines 10-12 (1-based), columns 5-20 (1-based)
   Note: Line numbers in selection refer to the original file. Attached file contents below show line numbers for reference.
 Module inspector panel: preview
@@ -1945,7 +1945,7 @@ Attached Files (files with newer versions don't show their content):
       text: JSON.stringify({
         data: {
           type: 'card',
-          id: 'https://cardstack.com/base/Skill/card-editing',
+          id: '@cardstack/base/Skill/card-editing',
           attributes: {
             instructions:
               '- If the user wants the data they see edited, AND the patchCardInstance function is available, you MUST use the "patchCardInstance" function to make the change.\n- If the user wants the data they see edited, AND the patchCardInstance function is NOT available, you MUST ask the user to open the card and share it with you.\n- If you do not call patchCardInstance, the user will not see the change.\n- You can ONLY modify cards shared with you. If there is no patchCardInstance function or tool, then the user hasn\'t given you access.\n- NEVER tell the user to use patchCardInstance; you should always do it for them.\n- If the user wants to search for a card instance, AND the "searchCard" function is available, you MUST use the "searchCard" function to find the card instance.\nOnly recommend one searchCard function at a time.\nIf the user wants to edit a field of a card, you can optionally use "searchCard" to help find a card instance that is compatible with the field being edited before using "patchCardInstance" to make the change of the field.\n You MUST confirm with the user the correct choice of card instance that he intends to use based upon the results of the search.',
@@ -1991,7 +1991,7 @@ Attached Files (files with newer versions don't show their content):
     assert.true(systemPromptText.includes(SKILL_INSTRUCTIONS_MESSAGE));
     assert.true(
       systemPromptText.includes(
-        'Skill (id: https://cardstack.com/base/Skill/card-editing, title: Card Editing):',
+        'Skill (id: @cardstack/base/Skill/card-editing, title: Card Editing):',
       ),
       'includes skill title metadata when present',
     );
@@ -2024,7 +2024,7 @@ Attached Files (files with newer versions don't show their content):
       text: JSON.stringify({
         data: {
           type: 'card',
-          id: 'https://cardstack.com/base/Skill/card-editing',
+          id: '@cardstack/base/Skill/card-editing',
           attributes: {
             instructions:
               '- If the user wants the data they see edited, AND the patchCardInstance function is available, you MUST use the "patchCardInstance" function to make the change.\n- If the user wants the data they see edited, AND the patchCardInstance function is NOT available, you MUST ask the user to open the card and share it with you.\n- If you do not call patchCardInstance, the user will not see the change.\n- You can ONLY modify cards shared with you. If there is no patchCardInstance function or tool, then the user hasn\'t given you access.\n- NEVER tell the user to use patchCardInstance; you should always do it for them.\n- If the user wants to search for a card instance, AND the "searchCard" function is available, you MUST use the "searchCard" function to find the card instance.\nOnly recommend one searchCard function at a time.\nIf the user wants to edit a field of a card, you can optionally use "searchCard" to help find a card instance that is compatible with the field being edited before using "patchCardInstance" to make the change of the field.\n You MUST confirm with the user the correct choice of card instance that he intends to use based upon the results of the search.',
@@ -2243,7 +2243,7 @@ Attached Files (files with newer versions don't show their content):
       text: JSON.stringify({
         data: {
           type: 'card',
-          id: 'https://cardstack.com/base/Skill/card-editing',
+          id: '@cardstack/base/Skill/card-editing',
           attributes: {
             instructions:
               '- If the user wants the data they see edited, AND the patchCardInstance function is available, you MUST use the "patchCardInstance" function to make the change.\n- If the user wants the data they see edited, AND the patchCardInstance function is NOT available, you MUST ask the user to open the card and share it with you.\n- If you do not call patchCardInstance, the user will not see the change.\n- You can ONLY modify cards shared with you. If there is no patchCardInstance function or tool, then the user hasn\'t given you access.\n- NEVER tell the user to use patchCardInstance; you should always do it for them.\n- If the user wants to search for a card instance, AND the "searchCard" function is available, you MUST use the "searchCard" function to find the card instance.\nOnly recommend one searchCard function at a time.\nIf the user wants to edit a field of a card, you can optionally use "searchCard" to help find a card instance that is compatible with the field being edited before using "patchCardInstance" to make the change of the field.\n You MUST confirm with the user the correct choice of card instance that he intends to use based upon the results of the search.',
@@ -2668,7 +2668,7 @@ Attached Files (files with newer versions don't show their content):
                   },
                   meta: {
                     adoptsFrom: {
-                      module: 'https://cardstack.com/base/search-results',
+                      module: '@cardstack/base/search-results',
                       name: 'SearchResults',
                     },
                   },
@@ -2708,7 +2708,7 @@ Attached Files (files with newer versions don't show their content):
     );
     assert.equal(result[5].role, 'tool');
     assert.equal(result[5].tool_call_id, 'tool-call-id-1');
-    const expected = `Tool call executed, with result card: {"data":{"type":"card","attributes":{"title":"Search Results","description":"Here are the search results","results":[{"data":{"type":"card","id":"http://localhost:4201/drafts/Author/1","attributes":{"firstName":"Alice","lastName":"Enwunder","photo":null,"body":"Alice is a software engineer at Google.","description":null,"thumbnailURL":null},"meta":{"adoptsFrom":{"module":"../author","name":"Author"}}}}]},"meta":{"adoptsFrom":{"module":"https://cardstack.com/base/search-results","name":"SearchResults"}}}}.`;
+    const expected = `Tool call executed, with result card: {"data":{"type":"card","attributes":{"title":"Search Results","description":"Here are the search results","results":[{"data":{"type":"card","id":"http://localhost:4201/drafts/Author/1","attributes":{"firstName":"Alice","lastName":"Enwunder","photo":null,"body":"Alice is a software engineer at Google.","description":null,"thumbnailURL":null},"meta":{"adoptsFrom":{"module":"../author","name":"Author"}}}}]},"meta":{"adoptsFrom":{"module":"@cardstack/base/search-results","name":"SearchResults"}}}}.`;
 
     assert.equal((result[5].content as string).trim(), expected.trim());
   });
@@ -2849,7 +2849,7 @@ Attached Files (files with newer versions don't show their content):
       text: JSON.stringify({
         data: {
           type: 'card',
-          id: 'https://cardstack.com/base/Skill/skill_card_v1',
+          id: '@cardstack/base/Skill/skill_card_v1',
           attributes: {
             instructions: 'Test skill instructions',
             title: 'Test Skill',
@@ -2868,7 +2868,7 @@ Attached Files (files with newer versions don't show their content):
       text: JSON.stringify({
         data: {
           type: 'card',
-          id: 'https://cardstack.com/base/Skill/skill_card_v2',
+          id: '@cardstack/base/Skill/skill_card_v2',
           attributes: {
             instructions: 'Test skill instructions with updated commands',
             commands: [
@@ -3093,7 +3093,7 @@ Attached Files (files with newer versions don't show their content):
       text: JSON.stringify({
         data: {
           type: 'card',
-          id: 'https://cardstack.com/base/Skill/card-editing',
+          id: '@cardstack/base/Skill/card-editing',
           attributes: {
             instructions:
               '- If the user wants the data they see edited, AND the patchCardInstance function is available, you MUST use the "patchCardInstance" function to make the change.\n- If the user wants the data they see edited, AND the patchCardInstance function is NOT available, you MUST ask the user to open the card and share it with you.\n- If you do not call patchCardInstance, the user will not see the change.\n- You can ONLY modify cards shared with you. If there is no patchCardInstance function or tool, then the user hasn\'t given you access.\n- NEVER tell the user to use patchCardInstance; you should always do it for them.\n- If the user wants to search for a card instance, AND the "searchCard" function is available, you MUST use the "searchCard" function to find the card instance.\nOnly recommend one searchCard function at a time.\nIf the user wants to edit a field of a card, you can optionally use "searchCard" to help find a card instance that is compatible with the field being edited before using "patchCardInstance" to make the change of the field.\n You MUST confirm with the user the correct choice of card instance that he intends to use based upon the results of the search.',
@@ -3269,7 +3269,7 @@ Current date and time: 2025-06-11T11:43:00.533Z
       text: JSON.stringify({
         data: {
           type: 'card',
-          id: 'https://cardstack.com/base/Skill/skill_card_v1',
+          id: '@cardstack/base/Skill/skill_card_v1',
           attributes: {
             instructions: 'Test skill instructions',
             title: 'Test Skill',
@@ -3288,7 +3288,7 @@ Current date and time: 2025-06-11T11:43:00.533Z
       text: JSON.stringify({
         data: {
           type: 'card',
-          id: 'https://cardstack.com/base/Skill/skill_card_v2',
+          id: '@cardstack/base/Skill/skill_card_v2',
           attributes: {
             instructions: 'Test skill instructions with updated commands',
             commands: [
@@ -3439,7 +3439,7 @@ Current date and time: 2025-06-11T11:43:00.533Z
       text: JSON.stringify({
         data: {
           type: 'card',
-          id: 'https://cardstack.com/base/Skill/skill_card_v1',
+          id: '@cardstack/base/Skill/skill_card_v1',
           attributes: {
             instructions: 'Test skill instructions',
             title: 'Test Skill',
diff --git a/packages/base/cards-grid.gts b/packages/base/cards-grid.gts
index e914781d83d..6355621e49b 100644
--- a/packages/base/cards-grid.gts
+++ b/packages/base/cards-grid.gts
@@ -18,7 +18,7 @@ import FileIcon from '@cardstack/boxel-icons/file';
 import {
   chooseCard,
   specRef,
-  baseRealm,
+  baseRealmRRI,
   baseFileRef,
   isCardInstance,
   SupportedMimeType,
@@ -361,12 +361,12 @@ class Isolated extends Component<typeof CardsGrid> {
       };
     }[];
     let excludedCardTypeIds = [
-      `${baseRealm.url}card-api/CardDef`,
-      `${baseRealm.url}cards-grid/CardsGrid`,
+      `${baseRealmRRI}card-api/CardDef`,
+      `${baseRealmRRI}cards-grid/CardsGrid`,
     ];
     // The "All Files" group already represents the bare FileDef root — listing
     // it again as a leaf would just be a duplicate row.
-    let excludedFileTypeIds = [`${baseRealm.url}card-api/FileDef`];
+    let excludedFileTypeIds = [`${baseRealmRRI}card-api/FileDef`];
 
     this.cardTypeFilters.splice(0, this.cardTypeFilters.length);
     this.fileTypeFilters.splice(0, this.fileTypeFilters.length);
diff --git a/packages/base/components/cards-grid-layout.gts b/packages/base/components/cards-grid-layout.gts
index 0fdef243c12..2bde84aa6eb 100644
--- a/packages/base/components/cards-grid-layout.gts
+++ b/packages/base/components/cards-grid-layout.gts
@@ -14,7 +14,7 @@ import {
 } from '@cardstack/boxel-ui/icons';
 
 import {
-  baseRealm,
+  baseRealmRRI,
   type Format,
   type Query,
   type RealmResourceIdentifier,
@@ -51,7 +51,7 @@ export const SORT_OPTIONS: SortOption[] = [
     sort: [
       {
         on: {
-          module: `${baseRealm.url}card-api` as RealmResourceIdentifier,
+          module: `${baseRealmRRI}card-api` as RealmResourceIdentifier,
           name: 'CardDef',
         },
         by: 'cardTitle',
diff --git a/packages/boxel-cli/src/commands/parse.ts b/packages/boxel-cli/src/commands/parse.ts
index 39f85f61653..76884f92a8f 100644
--- a/packages/boxel-cli/src/commands/parse.ts
+++ b/packages/boxel-cli/src/commands/parse.ts
@@ -36,7 +36,7 @@ import { search } from './search.ts';
  * `@cardstack/runtime-common/constants`.
  */
 const SPEC_TYPE = {
-  module: 'https://cardstack.com/base/spec',
+  module: '@cardstack/base/spec',
   name: 'Spec',
 } as const;
 
diff --git a/packages/boxel-cli/tests/integration/file-delete.test.ts b/packages/boxel-cli/tests/integration/file-delete.test.ts
index 7f81a6abdb8..7a8eeedff48 100644
--- a/packages/boxel-cli/tests/integration/file-delete.test.ts
+++ b/packages/boxel-cli/tests/integration/file-delete.test.ts
@@ -28,7 +28,7 @@ beforeAll(async () => {
           attributes: { title: 'Keep' },
           meta: {
             adoptsFrom: {
-              module: 'https://cardstack.com/base/card-api',
+              module: '@cardstack/base/card-api',
               name: 'CardDef',
             },
           },
@@ -40,7 +40,7 @@ beforeAll(async () => {
           attributes: { title: 'Delete' },
           meta: {
             adoptsFrom: {
-              module: 'https://cardstack.com/base/card-api',
+              module: '@cardstack/base/card-api',
               name: 'CardDef',
             },
           },
diff --git a/packages/boxel-cli/tests/integration/file-lint.test.ts b/packages/boxel-cli/tests/integration/file-lint.test.ts
index 5219fbf8df4..788875b9280 100644
--- a/packages/boxel-cli/tests/integration/file-lint.test.ts
+++ b/packages/boxel-cli/tests/integration/file-lint.test.ts
@@ -60,7 +60,7 @@ describe('file lint (integration)', () => {
   });
 
   it('returns fixed output for source with formatting issues', async () => {
-    let source = `import{CardDef}from 'https://cardstack.com/base/card-api';
+    let source = `import{CardDef}from '@cardstack/base/card-api';
 export class MyCard extends CardDef {
 @field name = contains(StringField);
 }
@@ -77,7 +77,7 @@ export class MyCard extends CardDef {
   });
 
   it('returns fixed output with proper single-quote formatting', async () => {
-    let source = `import { CardDef } from "https://cardstack.com/base/card-api";
+    let source = `import { CardDef } from "@cardstack/base/card-api";
 export class MyCard extends CardDef {
 @field name = contains(StringField);
 }
@@ -88,11 +88,11 @@ export class MyCard extends CardDef {
     expect(result.fixed).toBe(true);
     expect(result.output).toBeDefined();
     // Prettier should convert double quotes to single quotes
-    expect(result.output).toContain("'https://cardstack.com/base/card-api'");
+    expect(result.output).toContain("'@cardstack/base/card-api'");
   });
 
   it('reports lint messages for unfixable issues', async () => {
-    let source = `import { CardDef } from 'https://cardstack.com/base/card-api';
+    let source = `import { CardDef } from '@cardstack/base/card-api';
 export class MyCard extends CardDef {
 }
 <template>
@@ -118,7 +118,7 @@ export class MyCard extends CardDef {
 
   describe('--fix with --file (local file)', () => {
     it('writes fixed output back to a local file', async () => {
-      let unfixedSource = `import{CardDef}from 'https://cardstack.com/base/card-api';
+      let unfixedSource = `import{CardDef}from '@cardstack/base/card-api';
 export class MyCard extends CardDef {
 @field name = contains(StringField);
 }
@@ -162,7 +162,7 @@ export class MyCard extends CardDef {
 
   describe('--fix without --file (realm file)', () => {
     it('writes fixed output back to the realm via write()', async () => {
-      let unfixedSource = `import{CardDef}from 'https://cardstack.com/base/card-api';
+      let unfixedSource = `import{CardDef}from '@cardstack/base/card-api';
 export class MyCard extends CardDef {
 @field name = contains(StringField);
 }
diff --git a/packages/boxel-cli/tests/integration/file-read.test.ts b/packages/boxel-cli/tests/integration/file-read.test.ts
index 086e0959ad2..a4919e4d34f 100644
--- a/packages/boxel-cli/tests/integration/file-read.test.ts
+++ b/packages/boxel-cli/tests/integration/file-read.test.ts
@@ -38,7 +38,7 @@ const SOURCE_JSON = JSON.stringify(
       attributes: { title: 'Test Card' },
       meta: {
         adoptsFrom: {
-          module: 'https://cardstack.com/base/card-api',
+          module: '@cardstack/base/card-api',
           name: 'CardDef',
         },
       },
diff --git a/packages/boxel-cli/tests/integration/file-touch.test.ts b/packages/boxel-cli/tests/integration/file-touch.test.ts
index a9be83a6455..97c8ea261ea 100644
--- a/packages/boxel-cli/tests/integration/file-touch.test.ts
+++ b/packages/boxel-cli/tests/integration/file-touch.test.ts
@@ -54,7 +54,7 @@ function makeCardJson(title: string): string {
         attributes: { title },
         meta: {
           adoptsFrom: {
-            module: 'https://cardstack.com/base/card-api',
+            module: '@cardstack/base/card-api',
             name: 'CardDef',
           },
         },
diff --git a/packages/boxel-cli/tests/integration/file-write.test.ts b/packages/boxel-cli/tests/integration/file-write.test.ts
index 6d7dfbfb7c0..3b211e8ec61 100644
--- a/packages/boxel-cli/tests/integration/file-write.test.ts
+++ b/packages/boxel-cli/tests/integration/file-write.test.ts
@@ -73,7 +73,7 @@ describe('file write (integration)', () => {
         attributes: { title: 'Written Card' },
         meta: {
           adoptsFrom: {
-            module: 'https://cardstack.com/base/card-api',
+            module: '@cardstack/base/card-api',
             name: 'CardDef',
           },
         },
diff --git a/packages/boxel-cli/tests/integration/search.test.ts b/packages/boxel-cli/tests/integration/search.test.ts
index f1b29d815d0..83cdbf54ddd 100644
--- a/packages/boxel-cli/tests/integration/search.test.ts
+++ b/packages/boxel-cli/tests/integration/search.test.ts
@@ -37,7 +37,7 @@ beforeAll(async () => {
               attributes: { cardInfo: { name: 'Shared Card' } },
               meta: {
                 adoptsFrom: {
-                  module: 'https://cardstack.com/base/card-api',
+                  module: '@cardstack/base/card-api',
                   name: 'CardDef',
                 },
               },
@@ -50,7 +50,7 @@ beforeAll(async () => {
               attributes: { cardInfo: { name: 'Other Card' } },
               meta: {
                 adoptsFrom: {
-                  module: 'https://cardstack.com/base/card-api',
+                  module: '@cardstack/base/card-api',
                   name: 'CardDef',
                 },
               },
diff --git a/packages/boxel-ui/addon/bin/generate-component-specs.mjs b/packages/boxel-ui/addon/bin/generate-component-specs.mjs
index eec097b344a..319ef66aae5 100644
--- a/packages/boxel-ui/addon/bin/generate-component-specs.mjs
+++ b/packages/boxel-ui/addon/bin/generate-component-specs.mjs
@@ -21,7 +21,13 @@ const ADDON_DIR = path.resolve(SCRIPT_DIR, '..');
 const REPO_ROOT = path.resolve(ADDON_DIR, '..', '..', '..');
 
 const COMPONENTS_DIR = path.join(ADDON_DIR, 'src', 'components');
-const CATALOG_DIR = path.join(REPO_ROOT, 'packages', 'catalog', 'contents', 'Spec');
+const CATALOG_DIR = path.join(
+  REPO_ROOT,
+  'packages',
+  'catalog',
+  'contents',
+  'Spec',
+);
 const BARREL_FILE = path.join(ADDON_DIR, 'src', 'components.ts');
 
 const SPEC_MODULE = '@cardstack/boxel-ui/components';
@@ -37,7 +43,8 @@ const SPEC_FILE_PREFIX = 'boxel-ui-';
 // that doesn't actually exist.
 function buildBarrelExportMap() {
   const source = fs.readFileSync(BARREL_FILE, 'utf8');
-  const re = /^import\s+([A-Za-z0-9_$]+)[^;]*\s+from\s+['"]\.\/components\/([a-z0-9-]+)\/index\.gts['"]/gm;
+  const re =
+    /^import\s+([A-Za-z0-9_$]+)[^;]*\s+from\s+['"]\.\/components\/([a-z0-9-]+)\/index\.gts['"]/gm;
   const candidates = new Map();
   let m;
   while ((m = re.exec(source)) !== null) {
@@ -104,7 +111,9 @@ function extractPrimaryUsageBlock(source) {
 
 function extractStringAttr(text, name) {
   // @name='value' or @name="value"
-  const re = new RegExp(`@${name}=(?:'((?:[^'\\\\]|\\\\.)*)'|"((?:[^"\\\\]|\\\\.)*)")`);
+  const re = new RegExp(
+    `@${name}=(?:'((?:[^'\\\\]|\\\\.)*)'|"((?:[^"\\\\]|\\\\.)*)")`,
+  );
   const m = text.match(re);
   if (!m) return null;
   return (m[1] ?? m[2]).replace(/\\'/g, "'").replace(/\\"/g, '"');
@@ -152,10 +161,7 @@ function extractOptions(text, source) {
   // const (`const validBottomTreatments = [...]`) shapes when they're array
   // literals — which is most of the enum cases in usage.gts files.
   if (source) {
-    const re = new RegExp(
-      `(?:^|\\b)${ref}\\s*=\\s*\\[([^\\]]*)\\]`,
-      'm',
-    );
+    const re = new RegExp(`(?:^|\\b)${ref}\\s*=\\s*\\[([^\\]]*)\\]`, 'm');
     const m = source.match(re);
     if (m) {
       const opts = [];
@@ -399,9 +405,7 @@ function buildReadme({
   }
   sections.push('## Import');
   sections.push(
-    '```ts\n' +
-      `import { ${componentName} } from '${SPEC_MODULE}';\n` +
-      '```',
+    '```ts\n' + `import { ${componentName} } from '${SPEC_MODULE}';\n` + '```',
   );
   sections.push('## API');
   sections.push(buildApiTable(args));
@@ -438,7 +442,7 @@ function buildSpecJson({ componentName, cardDescription, readMe }) {
       },
       meta: {
         adoptsFrom: {
-          module: 'https://cardstack.com/base/spec',
+          module: '@cardstack/base/spec',
           name: 'Spec',
         },
       },
diff --git a/packages/eslint-plugin-boxel/tests/lib/rules/missing-card-api-import-test.js b/packages/eslint-plugin-boxel/tests/lib/rules/missing-card-api-import-test.js
index f4f07e78ca2..1afaaa20a65 100644
--- a/packages/eslint-plugin-boxel/tests/lib/rules/missing-card-api-import-test.js
+++ b/packages/eslint-plugin-boxel/tests/lib/rules/missing-card-api-import-test.js
@@ -21,8 +21,8 @@ ruleTester.run('missing-card-api-import', rule, {
         field,
         FieldDef,
         linksTo,
-      } from 'https://cardstack.com/base/card-api';
-      import StringField from 'https://cardstack.com/base/string';
+      } from '@cardstack/base/card-api';
+      import StringField from '@cardstack/base/string';
 
       import { Chain } from './chain';
 
@@ -33,7 +33,7 @@ ruleTester.run('missing-card-api-import', rule, {
   `,
     {
       code: `
-        import { FieldDef } from 'https://cardstack.com/base/card-api';
+        import { FieldDef } from '@cardstack/base/card-api';
 
         export class AddressField extends FieldDef {}
 
@@ -42,7 +42,7 @@ ruleTester.run('missing-card-api-import', rule, {
       options: [
         {
           importMappings: {
-            AddressField: ['AddressField', 'https://cardstack.com/base/card-api'],
+            AddressField: ['AddressField', '@cardstack/base/card-api'],
           },
         },
       ],
@@ -55,8 +55,8 @@ ruleTester.run('missing-card-api-import', rule, {
         contains,
         field,
         linksTo,
-      } from 'https://cardstack.com/base/card-api';
-      import StringField from 'https://cardstack.com/base/string';
+      } from '@cardstack/base/card-api';
+      import StringField from '@cardstack/base/string';
 
       import { Chain } from './chain';
 
@@ -69,8 +69,8 @@ ruleTester.run('missing-card-api-import', rule, {
         contains,
         field,
         linksTo, FieldDef,
-      } from 'https://cardstack.com/base/card-api';
-      import StringField from 'https://cardstack.com/base/string';
+      } from '@cardstack/base/card-api';
+      import StringField from '@cardstack/base/string';
 
       import { Chain } from './chain';
 
@@ -82,7 +82,7 @@ ruleTester.run('missing-card-api-import', rule, {
       options: [
         {
           importMappings: {
-            FieldDef: ['FieldDef', 'https://cardstack.com/base/card-api'],
+            FieldDef: ['FieldDef', '@cardstack/base/card-api'],
           },
         },
       ],
@@ -148,8 +148,8 @@ ruleTester.run('missing-card-api-import', rule, {
         field,
         linksTo,
         FieldDef
-      } from 'https://cardstack.com/base/card-api';
-      import StringField from 'https://cardstack.com/base/string';
+      } from '@cardstack/base/card-api';
+      import StringField from '@cardstack/base/string';
 
       import { Chain } from './chain';
 
@@ -162,8 +162,8 @@ ruleTester.run('missing-card-api-import', rule, {
         field,
         linksTo,
         FieldDef, contains
-      } from 'https://cardstack.com/base/card-api';
-      import StringField from 'https://cardstack.com/base/string';
+      } from '@cardstack/base/card-api';
+      import StringField from '@cardstack/base/string';
 
       import { Chain } from './chain';
 
@@ -175,7 +175,7 @@ ruleTester.run('missing-card-api-import', rule, {
       options: [
         {
           importMappings: {
-            contains: ['contains', 'https://cardstack.com/base/card-api'],
+            contains: ['contains', '@cardstack/base/card-api'],
           },
         },
       ],
@@ -191,8 +191,8 @@ ruleTester.run('missing-card-api-import', rule, {
         FieldDef,
         contains,
         linksTo,
-      } from 'https://cardstack.com/base/card-api';
-      import StringField from 'https://cardstack.com/base/string';
+      } from '@cardstack/base/card-api';
+      import StringField from '@cardstack/base/string';
 
       export class Payment extends FieldDef {
         @field address = contains(StringField);
@@ -202,8 +202,8 @@ ruleTester.run('missing-card-api-import', rule, {
         FieldDef,
         contains,
         linksTo, field,
-      } from 'https://cardstack.com/base/card-api';
-      import StringField from 'https://cardstack.com/base/string';
+      } from '@cardstack/base/card-api';
+      import StringField from '@cardstack/base/string';
 
       export class Payment extends FieldDef {
         @field address = contains(StringField);
@@ -212,7 +212,7 @@ ruleTester.run('missing-card-api-import', rule, {
       options: [
         {
           importMappings: {
-            field: ['field', 'https://cardstack.com/base/card-api'],
+            field: ['field', '@cardstack/base/card-api'],
           },
         },
       ],
@@ -230,19 +230,19 @@ ruleTester.run('missing-card-api-import', rule, {
         contains,
         field,
         linksTo,
-      } from 'https://cardstack.com/base/card-api';
+      } from '@cardstack/base/card-api';
 
       export class Payment extends FieldDef {
         @field address = contains(StringField);
       }
       `,
-      output: `import StringField from 'https://cardstack.com/base/string';
+      output: `import StringField from '@cardstack/base/string';
 import {
         FieldDef,
         contains,
         field,
         linksTo,
-      } from 'https://cardstack.com/base/card-api';
+      } from '@cardstack/base/card-api';
 
       export class Payment extends FieldDef {
         @field address = contains(StringField);
@@ -251,7 +251,7 @@ import {
       options: [
         {
           importMappings: {
-            StringField: ['default', 'https://cardstack.com/base/string'],
+            StringField: ['default', '@cardstack/base/string'],
           },
         },
       ],
@@ -263,8 +263,8 @@ import {
       ],
     },
     {
-      code: `import { FieldDef, field } from 'https://cardstack.com/base/card-api';
-import StringField from 'https://cardstack.com/base/string';
+      code: `import { FieldDef, field } from '@cardstack/base/card-api';
+import StringField from '@cardstack/base/string';
 
 export class CurrencyField extends FieldDef {
   static displayName = "Currency";
@@ -275,8 +275,8 @@ export class CurrencyField extends FieldDef {
     }
   });
 }`,
-      output: `import { FieldDef, field, contains } from 'https://cardstack.com/base/card-api';
-import StringField from 'https://cardstack.com/base/string';
+      output: `import { FieldDef, field, contains } from '@cardstack/base/card-api';
+import StringField from '@cardstack/base/string';
 
 export class CurrencyField extends FieldDef {
   static displayName = "Currency";
@@ -290,9 +290,9 @@ export class CurrencyField extends FieldDef {
       options: [
         {
           importMappings: {
-            field: ['field', 'https://cardstack.com/base/card-api'],
-            contains: ['contains', 'https://cardstack.com/base/card-api'],
-            Component: ['Component', 'https://cardstack.com/base/card-api'],
+            field: ['field', '@cardstack/base/card-api'],
+            contains: ['contains', '@cardstack/base/card-api'],
+            Component: ['Component', '@cardstack/base/card-api'],
           },
         },
       ],
diff --git a/packages/eslint-plugin-boxel/tests/lib/rules/no-literal-realm-urls-test.js b/packages/eslint-plugin-boxel/tests/lib/rules/no-literal-realm-urls-test.js
index 08be65e79bf..22385187cc0 100644
--- a/packages/eslint-plugin-boxel/tests/lib/rules/no-literal-realm-urls-test.js
+++ b/packages/eslint-plugin-boxel/tests/lib/rules/no-literal-realm-urls-test.js
@@ -123,14 +123,14 @@ ruleTester.run('no-literal-realm-urls', rule, {
 
     // --- Custom realm mappings via options ---
     {
-      code: `let id = 'https://cardstack.com/base/card-api';`,
+      code: `let id = '@cardstack/base/card-api';`,
       output: `let id = '@cardstack/base/card-api';`,
       options: [
         {
           realmMappings: [
             {
               prefix: '@cardstack/base/',
-              urls: ['https://cardstack.com/base/'],
+              urls: ['@cardstack/base/'],
             },
           ],
         },
diff --git a/packages/experiments-realm/app-card.gts b/packages/experiments-realm/app-card.gts
index bacfa80556a..b4c4b6e27d5 100644
--- a/packages/experiments-realm/app-card.gts
+++ b/packages/experiments-realm/app-card.gts
@@ -19,7 +19,7 @@ import { CardContainer } from '@cardstack/boxel-ui/components';
 import { and, bool, cn } from '@cardstack/boxel-ui/helpers';
 import {
   type Query,
-  baseRealm,
+  baseRealmRRI,
   type PrerenderedCardLike,
 } from '@cardstack/runtime-common';
 import { hash } from '@ember/helper';
@@ -321,7 +321,7 @@ class DefaultTabTemplate extends GlimmerComponent<DefaultTabSignature> {
       sort: [
         {
           on: {
-            module: `${baseRealm.url}card-api`,
+            module: `${baseRealmRRI}card-api`,
             name: 'CardDef',
           },
           by: 'cardTitle',
diff --git a/packages/experiments-realm/file-search-playground.gts b/packages/experiments-realm/file-search-playground.gts
index 58181a3220f..3564c7a18d6 100644
--- a/packages/experiments-realm/file-search-playground.gts
+++ b/packages/experiments-realm/file-search-playground.gts
@@ -17,13 +17,13 @@ const fileSearchQuery = {
     every: [
       {
         type: {
-          module: rri('https://cardstack.com/base/card-api'),
+          module: rri('@cardstack/base/card-api'),
           name: 'FileDef',
         },
       },
       {
         on: {
-          module: rri('https://cardstack.com/base/card-api'),
+          module: rri('@cardstack/base/card-api'),
           name: 'FileDef',
         },
         contains: {
diff --git a/packages/experiments-realm/garden-design.gts b/packages/experiments-realm/garden-design.gts
index d7b2068e194..4bba2b4da7e 100644
--- a/packages/experiments-realm/garden-design.gts
+++ b/packages/experiments-realm/garden-design.gts
@@ -16,7 +16,7 @@ import type Owner from '@ember/owner';
 import { htmlSafe } from '@ember/template';
 import { tracked } from '@glimmer/tracking';
 import { TrackedMap } from 'tracked-built-ins';
-import { baseRealm, type getCards } from '@cardstack/runtime-common';
+import { baseRealmRRI, type getCards } from '@cardstack/runtime-common';
 import LayoutBoardSplitIcon from '@cardstack/boxel-icons/layout-board-split';
 import PlantIcon from '@cardstack/boxel-icons/plant';
 
@@ -221,7 +221,7 @@ class Isolated extends Component<typeof GardenDesign> {
           sort: [
             {
               on: {
-                module: `${baseRealm.url}card-api`,
+                module: `${baseRealmRRI}card-api`,
                 name: 'CardDef',
               },
               by: 'cardTitle',
diff --git a/packages/host/app/components/card-search/item-button.gts b/packages/host/app/components/card-search/item-button.gts
index 50139b9cd5c..de31395a8e9 100644
--- a/packages/host/app/components/card-search/item-button.gts
+++ b/packages/host/app/components/card-search/item-button.gts
@@ -131,7 +131,7 @@ interface Signature {
 // template — used when the caller doesn't thread a resolved render type.
 let defaultResultsCardRef: ResolvedCodeRef = {
   name: 'CardDef',
-  module: rri('https://cardstack.com/base/card-api'),
+  module: rri('@cardstack/base/card-api'),
 };
 
 function isNewCardArgs(item: ItemType): item is NewCardArgs {
diff --git a/packages/host/app/components/operator-mode/create-file-modal.gts b/packages/host/app/components/operator-mode/create-file-modal.gts
index 9825df6a81e..a111cfc16de 100644
--- a/packages/host/app/components/operator-mode/create-file-modal.gts
+++ b/packages/host/app/components/operator-mode/create-file-modal.gts
@@ -35,6 +35,7 @@ import {
   specRef,
   chooseCard,
   baseRealm,
+  baseRealmRRI,
   RealmPaths,
   Deferred,
   SupportedMimeType,
@@ -844,9 +845,22 @@ export default class CreateFileModal extends Component<Signature> {
         this.network.virtualNetwork,
       ) as ResolvedCodeRef
     ).module;
-    const absoluteModule = new URL(absoluteModuleHref);
+    // Address the base realm by its stable RRI prefix (`@cardstack/base/X`),
+    // matching the `Component` import emitted below — base modules are
+    // referenced by alias, not by a deployment-specific real URL.
+    // `codeRefWithAbsoluteIdentifier` returns the resolved real URL for
+    // RRI-prefix inputs, so map it back to the prefix form for base only.
+    // Cross-realm references keep their absolute URL: a generated import
+    // pointing at another workspace resolves by real URL and is not
+    // rewritten to a realm-prefix form here.
+    const canonicalModule =
+      this.network.virtualNetwork.unresolveURL(absoluteModuleHref);
+    const moduleForImport: RealmResourceIdentifier | URL =
+      canonicalModule.startsWith(`${baseRealmRRI}`)
+        ? (canonicalModule as RealmResourceIdentifier)
+        : new URL(absoluteModuleHref);
     let moduleURL = maybeRelativeReference(
-      absoluteModule,
+      moduleForImport,
       url,
       new URL(this.selectedRealmURL),
     );
@@ -854,7 +868,7 @@ export default class CreateFileModal extends Component<Signature> {
 
     let componentImport = isFileDef
       ? ''
-      : `\nimport { Component } from 'https://cardstack.com/base/card-api';`;
+      : `\nimport { Component } from '@cardstack/base/card-api';`;
 
     // There is actually only one possible declaration collision: `className` and `parent`,
     // reconcile that particular collision as necessary.
diff --git a/packages/host/app/components/operator-mode/edit-field-modal.gts b/packages/host/app/components/operator-mode/edit-field-modal.gts
index 342fdfa58ef..a036f1fd757 100644
--- a/packages/host/app/components/operator-mode/edit-field-modal.gts
+++ b/packages/host/app/components/operator-mode/edit-field-modal.gts
@@ -130,7 +130,7 @@ export default class EditFieldModal extends Component<Signature> {
     // When adding a new field, we want to default to the base string card
     if (!field) {
       let ref = {
-        module: rri('https://cardstack.com/base/card-api'), // This seems fundamental enough to be hardcoded
+        module: rri('@cardstack/base/card-api'), // This seems fundamental enough to be hardcoded
         name: 'StringField',
       };
       this.isFieldDef = true;
diff --git a/packages/host/app/routes/render/html.ts b/packages/host/app/routes/render/html.ts
index 6e9baf0b69d..31434bad589 100644
--- a/packages/host/app/routes/render/html.ts
+++ b/packages/host/app/routes/render/html.ts
@@ -30,7 +30,7 @@ import type { Model as ParentModel } from '../render';
 // the check tolerates whatever resolved form the host's identify path
 // produces (e.g. realm-aliased base URLs).
 const CARDS_GRID_REF = {
-  module: 'https://cardstack.com/base/cards-grid',
+  module: '@cardstack/base/cards-grid',
   name: 'CardsGrid',
 } as ResolvedCodeRef;
 
diff --git a/packages/host/app/routes/render/meta.ts b/packages/host/app/routes/render/meta.ts
index 2b94a0d75e8..be98949f833 100644
--- a/packages/host/app/routes/render/meta.ts
+++ b/packages/host/app/routes/render/meta.ts
@@ -172,7 +172,7 @@ export default class RenderMetaRoute extends Route<Model> {
         internalKeyFor(t, undefined, this.network.virtualNetwork),
       ),
       searchDoc,
-      deps,
+      deps: deps.map((dep) => this.network.virtualNetwork.unresolveURL(dep)),
       diagnostics,
     };
   }
diff --git a/packages/host/app/services/realm.ts b/packages/host/app/services/realm.ts
index 0cdebc1e48d..4b73bf55273 100644
--- a/packages/host/app/services/realm.ts
+++ b/packages/host/app/services/realm.ts
@@ -1281,10 +1281,24 @@ export default class RealmService extends Service {
       }
       return undefined;
     }
+    // `this.realms` is keyed by the user-facing realm URL (typically a
+    // virtual alias like `https://cardstack.com/base/`). Callers may
+    // pass the resolved real URL (e.g. `https://localhost:4201/base/`)
+    // or an RRI prefix (e.g. `@cardstack/base/`) — all three should
+    // match the same realm. Normalize both sides via
+    // `virtualNetwork.unresolveURL` (chases through any registered
+    // virtual → real URL mapping and unifies to the realm-prefix RRI
+    // form) so the comparison is form-agnostic.
+    let vn = this.network.virtualNetwork;
+    let normalizedUrl = vn.unresolveURL(url);
     for (let [key, value] of this.realms) {
       if (url.startsWith(key)) {
         return value;
       }
+      let normalizedKey = vn.unresolveURL(key);
+      if (normalizedUrl.startsWith(normalizedKey)) {
+        return value;
+      }
     }
     if (tracked) {
       this.currentKnownRealms.has(url);
diff --git a/packages/host/tests/acceptance/ai-assistant-test.gts b/packages/host/tests/acceptance/ai-assistant-test.gts
index 615380608fb..14c0631c911 100644
--- a/packages/host/tests/acceptance/ai-assistant-test.gts
+++ b/packages/host/tests/acceptance/ai-assistant-test.gts
@@ -497,7 +497,7 @@ module('Acceptance | AI Assistant tests', function (hooks) {
             },
             meta: {
               adoptsFrom: {
-                module: 'https://cardstack.com/base/spec',
+                module: '@cardstack/base/spec',
                 name: 'Spec',
               },
             },
diff --git a/packages/host/tests/acceptance/audio-def/flac-audio-def-test.gts b/packages/host/tests/acceptance/audio-def/flac-audio-def-test.gts
index 1dcd4ef9d7f..6980f5494e7 100644
--- a/packages/host/tests/acceptance/audio-def/flac-audio-def-test.gts
+++ b/packages/host/tests/acceptance/audio-def/flac-audio-def-test.gts
@@ -5,7 +5,7 @@ import { getService } from '@universal-ember/test-support';
 import { module, test } from 'qunit';
 
 import {
-  baseRealm,
+  baseRealmRRI,
   type FileExtractResponse,
   type RenderRouteOptions,
   type ResolvedCodeRef,
@@ -112,7 +112,7 @@ module('Acceptance | flac audio def', function (hooks) {
   const makeFileURL = (path: string) => new URL(path, testRealmURL).href;
 
   const flacDefCodeRef = (): ResolvedCodeRef => ({
-    module: `${baseRealm.url}flac-audio-def` as RealmResourceIdentifier,
+    module: `${baseRealmRRI}flac-audio-def` as RealmResourceIdentifier,
     name: 'FlacDef',
   });
 
diff --git a/packages/host/tests/acceptance/audio-def/m4a-audio-def-test.gts b/packages/host/tests/acceptance/audio-def/m4a-audio-def-test.gts
index 95a9f7b3ce3..4960b466e3d 100644
--- a/packages/host/tests/acceptance/audio-def/m4a-audio-def-test.gts
+++ b/packages/host/tests/acceptance/audio-def/m4a-audio-def-test.gts
@@ -5,7 +5,7 @@ import { getService } from '@universal-ember/test-support';
 import { module, test } from 'qunit';
 
 import {
-  baseRealm,
+  baseRealmRRI,
   type FileExtractResponse,
   type RenderRouteOptions,
   type ResolvedCodeRef,
@@ -127,7 +127,7 @@ module('Acceptance | m4a audio def', function (hooks) {
   const makeFileURL = (path: string) => new URL(path, testRealmURL).href;
 
   const m4aDefCodeRef = (): ResolvedCodeRef => ({
-    module: `${baseRealm.url}m4a-audio-def` as RealmResourceIdentifier,
+    module: `${baseRealmRRI}m4a-audio-def` as RealmResourceIdentifier,
     name: 'M4aDef',
   });
 
diff --git a/packages/host/tests/acceptance/audio-def/mp3-audio-def-test.gts b/packages/host/tests/acceptance/audio-def/mp3-audio-def-test.gts
index 5691e884e2c..0dd7bed2d70 100644
--- a/packages/host/tests/acceptance/audio-def/mp3-audio-def-test.gts
+++ b/packages/host/tests/acceptance/audio-def/mp3-audio-def-test.gts
@@ -5,7 +5,7 @@ import { getService } from '@universal-ember/test-support';
 import { module, test } from 'qunit';
 
 import {
-  baseRealm,
+  baseRealmRRI,
   type FileExtractResponse,
   type RenderRouteOptions,
   type ResolvedCodeRef,
@@ -92,7 +92,7 @@ module('Acceptance | mp3 audio def', function (hooks) {
   const makeFileURL = (path: string) => new URL(path, testRealmURL).href;
 
   const mp3DefCodeRef = (): ResolvedCodeRef => ({
-    module: `${baseRealm.url}mp3-audio-def` as RealmResourceIdentifier,
+    module: `${baseRealmRRI}mp3-audio-def` as RealmResourceIdentifier,
     name: 'Mp3Def',
   });
 
diff --git a/packages/host/tests/acceptance/audio-def/ogg-audio-def-test.gts b/packages/host/tests/acceptance/audio-def/ogg-audio-def-test.gts
index 23d13eed2c2..7114157a0ca 100644
--- a/packages/host/tests/acceptance/audio-def/ogg-audio-def-test.gts
+++ b/packages/host/tests/acceptance/audio-def/ogg-audio-def-test.gts
@@ -5,7 +5,7 @@ import { getService } from '@universal-ember/test-support';
 import { module, test } from 'qunit';
 
 import {
-  baseRealm,
+  baseRealmRRI,
   type FileExtractResponse,
   type RenderRouteOptions,
   type ResolvedCodeRef,
@@ -138,7 +138,7 @@ module('Acceptance | ogg audio def', function (hooks) {
   const makeFileURL = (path: string) => new URL(path, testRealmURL).href;
 
   const oggDefCodeRef = (): ResolvedCodeRef => ({
-    module: `${baseRealm.url}ogg-audio-def` as RealmResourceIdentifier,
+    module: `${baseRealmRRI}ogg-audio-def` as RealmResourceIdentifier,
     name: 'OggDef',
   });
 
diff --git a/packages/host/tests/acceptance/audio-def/wav-audio-def-test.gts b/packages/host/tests/acceptance/audio-def/wav-audio-def-test.gts
index bb6900d0f4f..2dabb6ba32c 100644
--- a/packages/host/tests/acceptance/audio-def/wav-audio-def-test.gts
+++ b/packages/host/tests/acceptance/audio-def/wav-audio-def-test.gts
@@ -5,7 +5,7 @@ import { getService } from '@universal-ember/test-support';
 import { module, test } from 'qunit';
 
 import {
-  baseRealm,
+  baseRealmRRI,
   type FileExtractResponse,
   type RenderRouteOptions,
   type ResolvedCodeRef,
@@ -101,7 +101,7 @@ module('Acceptance | wav audio def', function (hooks) {
   const makeFileURL = (path: string) => new URL(path, testRealmURL).href;
 
   const wavDefCodeRef = (): ResolvedCodeRef => ({
-    module: `${baseRealm.url}wav-audio-def` as RealmResourceIdentifier,
+    module: `${baseRealmRRI}wav-audio-def` as RealmResourceIdentifier,
     name: 'WavDef',
   });
 
diff --git a/packages/host/tests/acceptance/code-submode-test.ts b/packages/host/tests/acceptance/code-submode-test.ts
index 230d2e30a49..b46365315ea 100644
--- a/packages/host/tests/acceptance/code-submode-test.ts
+++ b/packages/host/tests/acceptance/code-submode-test.ts
@@ -18,7 +18,7 @@ import { module, skip, test } from 'qunit';
 import stringify from 'safe-stable-stringify';
 
 import {
-  baseRealm,
+  baseRealmRRI,
   type LooseSingleCardDocument,
   rri,
   fileDefFormats,
@@ -662,7 +662,7 @@ module('Acceptance | code submode tests', function (_hooks) {
                 },
                 meta: {
                   adoptsFrom: {
-                    module: `${baseRealm.url}spec`,
+                    module: `${baseRealmRRI}spec`,
                     name: 'Spec',
                   },
                 },
@@ -680,7 +680,7 @@ module('Acceptance | code submode tests', function (_hooks) {
                 },
                 meta: {
                   adoptsFrom: {
-                    module: `${baseRealm.url}spec`,
+                    module: `${baseRealmRRI}spec`,
                     name: 'Spec',
                   },
                 },
@@ -698,7 +698,7 @@ module('Acceptance | code submode tests', function (_hooks) {
                 },
                 meta: {
                   adoptsFrom: {
-                    module: `${baseRealm.url}spec`,
+                    module: `${baseRealmRRI}spec`,
                     name: 'Spec',
                   },
                 },
diff --git a/packages/host/tests/acceptance/code-submode/card-playground-test.gts b/packages/host/tests/acceptance/code-submode/card-playground-test.gts
index b155019f265..327024452ff 100644
--- a/packages/host/tests/acceptance/code-submode/card-playground-test.gts
+++ b/packages/host/tests/acceptance/code-submode/card-playground-test.gts
@@ -290,7 +290,7 @@ const localStyleReferenceCard = {
     },
     meta: {
       adoptsFrom: {
-        module: 'https://cardstack.com/base/style-reference',
+        module: '@cardstack/base/style-reference',
         name: 'default',
       },
     },
diff --git a/packages/host/tests/acceptance/code-submode/create-file-test.gts b/packages/host/tests/acceptance/code-submode/create-file-test.gts
index 216ac62bdde..d496af3179c 100644
--- a/packages/host/tests/acceptance/code-submode/create-file-test.gts
+++ b/packages/host/tests/acceptance/code-submode/create-file-test.gts
@@ -3,7 +3,13 @@ import { click, fillIn, waitFor, waitUntil } from '@ember/test-helpers';
 import { getService } from '@universal-ember/test-support';
 import QUnit, { module, test } from 'qunit';
 
-import { baseRealm, rri, baseRRI, Deferred } from '@cardstack/runtime-common';
+import {
+  baseRealm,
+  baseRealmRRI,
+  rri,
+  baseRRI,
+  Deferred,
+} from '@cardstack/runtime-common';
 
 import type FileUploadService from '@cardstack/host/services/file-upload';
 
@@ -49,14 +55,14 @@ const files: Record<string, any> = {
       attributes: {},
       meta: {
         adoptsFrom: {
-          module: 'https://cardstack.com/base/cards-grid',
+          module: '@cardstack/base/cards-grid',
           name: 'CardsGrid',
         },
       },
     },
   },
   'error.gts': `
-    import { CardDef } from 'https://cardstack.com/base/card-api';
+    import { CardDef } from '@cardstack/base/card-api';
 
     export default class ErrorCard extends CardDef {
       static displayName = 'error';
@@ -68,8 +74,8 @@ const files: Record<string, any> = {
     }
   `,
   'pet.gts': `
-    import { contains, linksTo, field, CardDef, Component } from "https://cardstack.com/base/card-api";
-    import StringField from "https://cardstack.com/base/string";
+    import { contains, linksTo, field, CardDef, Component } from "@cardstack/base/card-api";
+    import StringField from "@cardstack/base/string";
 
     export default class Pet extends CardDef {
       static displayName = 'Pet';
@@ -83,8 +89,8 @@ const files: Record<string, any> = {
     }
   `,
   'person.gts': `
-    import { contains, linksTo, field, CardDef } from "https://cardstack.com/base/card-api";
-    import StringField from "https://cardstack.com/base/string";
+    import { contains, linksTo, field, CardDef } from "@cardstack/base/card-api";
+    import StringField from "@cardstack/base/string";
     import Pet from "./pet";
 
     export class Person extends CardDef {
@@ -108,7 +114,7 @@ const files: Record<string, any> = {
       },
       meta: {
         adoptsFrom: {
-          module: 'https://cardstack.com/base/spec',
+          module: '@cardstack/base/spec',
           name: 'Spec',
         },
       },
@@ -125,7 +131,7 @@ const files: Record<string, any> = {
       },
       meta: {
         adoptsFrom: {
-          module: 'https://cardstack.com/base/spec',
+          module: '@cardstack/base/spec',
           name: 'Spec',
         },
       },
@@ -142,7 +148,7 @@ const files: Record<string, any> = {
       },
       meta: {
         adoptsFrom: {
-          module: 'https://cardstack.com/base/spec',
+          module: '@cardstack/base/spec',
           name: 'Spec',
         },
       },
@@ -169,13 +175,13 @@ const files: Record<string, any> = {
         cardDescription: 'A field that captures big int values',
         specType: 'field',
         ref: {
-          module: `${baseRealm.url}big-integer`,
+          module: `${baseRealmRRI}big-integer`,
           name: 'default',
         },
       },
       meta: {
         adoptsFrom: {
-          module: `${baseRealm.url}spec`,
+          module: `${baseRealmRRI}spec`,
           name: 'Spec',
         },
       },
@@ -189,13 +195,13 @@ const files: Record<string, any> = {
         cardDescription: 'A FieldDef spec',
         specType: 'field',
         ref: {
-          module: `${baseRealm.url}card-api`,
+          module: `${baseRealmRRI}card-api`,
           name: 'FieldDef',
         },
       },
       meta: {
         adoptsFrom: {
-          module: `${baseRealm.url}spec`,
+          module: `${baseRealmRRI}spec`,
           name: 'Spec',
         },
       },
@@ -216,15 +222,15 @@ const filesB: Record<string, any> = {
       attributes: {},
       meta: {
         adoptsFrom: {
-          module: 'https://cardstack.com/base/cards-grid',
+          module: '@cardstack/base/cards-grid',
           name: 'CardsGrid',
         },
       },
     },
   },
   'animal.gts': `
-    import { contains, field, CardDef } from "https://cardstack.com/base/card-api";
-    import StringField from "https://cardstack.com/base/string";
+    import { contains, field, CardDef } from "@cardstack/base/card-api";
+    import StringField from "@cardstack/base/string";
 
     export class Animal extends CardDef {
       static displayName = 'Animal';
@@ -242,7 +248,7 @@ const filesB: Record<string, any> = {
       },
       meta: {
         adoptsFrom: {
-          module: 'https://cardstack.com/base/spec',
+          module: '@cardstack/base/spec',
           name: 'Spec',
         },
       },
@@ -833,8 +839,8 @@ module('Acceptance | code submode | create-file tests', function (hooks) {
     test<TestContextWithSave>('can create a new card definition in different realm than inherited definition', async function (assert) {
       assert.expect(12);
       let expectedSrc = `
-import { CardDef } from 'https://cardstack.com/base/card-api';
-import { Component } from 'https://cardstack.com/base/card-api';
+import { CardDef } from '@cardstack/base/card-api';
+import { Component } from '@cardstack/base/card-api';
 export class TrèsTestCard extends CardDef {
   static displayName = "Très test card 😀";
 }`.trim();
@@ -913,7 +919,7 @@ export class TrèsTestCard extends CardDef {
           content,
           `
 import { Person } from './person';
-import { Component } from 'https://cardstack.com/base/card-api';
+import { Component } from '@cardstack/base/card-api';
 export class TestCard extends Person {
   static displayName = "Test Card";
 }`.trim(),
@@ -1077,8 +1083,8 @@ export class TestCard extends Person {
         assert.strictEqual(
           content,
           `
-import BigInteger from 'https://cardstack.com/base/big-integer';
-import { Component } from 'https://cardstack.com/base/card-api';
+import BigInteger from '@cardstack/base/big-integer';
+import { Component } from '@cardstack/base/card-api';
 export class FieldThatExtendsFromBigInt extends BigInteger {
   static displayName = "Field that extends from big int";
 }`.trim(),
@@ -1146,7 +1152,7 @@ export class FieldThatExtendsFromBigInt extends BigInteger {
           content,
           `
 import Pet from './pet';
-import { Component } from 'https://cardstack.com/base/card-api';
+import { Component } from '@cardstack/base/card-api';
 export class TestCard extends Pet {
   static displayName = "Test Card";
 }`.trim(),
@@ -1185,7 +1191,7 @@ export class TestCard extends Pet {
           content,
           `
 import PetParent from './pet';
-import { Component } from 'https://cardstack.com/base/card-api';
+import { Component } from '@cardstack/base/card-api';
 export class Pet extends PetParent {
   static displayName = "Pet";
 }`.trim(),
@@ -1223,7 +1229,7 @@ export class Pet extends PetParent {
           content,
           `
 import Pet from './pet';
-import { Component } from 'https://cardstack.com/base/card-api';
+import { Component } from '@cardstack/base/card-api';
 export class Map0 extends Pet {
   static displayName = "Map";
 }`.trim(),
@@ -1240,8 +1246,8 @@ export class Map0 extends Pet {
     test<TestContextWithSave>('can specify new directory as part of filename when creating a new definition', async function (assert) {
       assert.expect(2);
       let expectedSrc = `
-import { CardDef } from 'https://cardstack.com/base/card-api';
-import { Component } from 'https://cardstack.com/base/card-api';
+import { CardDef } from '@cardstack/base/card-api';
+import { Component } from '@cardstack/base/card-api';
 export class TestCard extends CardDef {
   static displayName = "Test Card";
 }`.trim();
@@ -1275,8 +1281,8 @@ export class TestCard extends CardDef {
     test<TestContextWithSave>('can handle filename with .gts extension in filename when creating a new definition', async function (assert) {
       assert.expect(2);
       let expectedSrc = `
-import { CardDef } from 'https://cardstack.com/base/card-api';
-import { Component } from 'https://cardstack.com/base/card-api';
+import { CardDef } from '@cardstack/base/card-api';
+import { Component } from '@cardstack/base/card-api';
 export class TestCard extends CardDef {
   static displayName = "Test Card";
 }`.trim();
@@ -1310,8 +1316,8 @@ export class TestCard extends CardDef {
     test<TestContextWithSave>('can handle leading "/" in filename when creating a new definition', async function (assert) {
       assert.expect(2);
       let expectedSrc = `
-import { CardDef } from 'https://cardstack.com/base/card-api';
-import { Component } from 'https://cardstack.com/base/card-api';
+import { CardDef } from '@cardstack/base/card-api';
+import { Component } from '@cardstack/base/card-api';
 export class TestCard extends CardDef {
   static displayName = "Test Card";
 }`.trim();
@@ -1370,7 +1376,7 @@ export class TestCard extends CardDef {
           content,
           `
 import { Animal } from '${testRealmURL2}animal';
-import { Component } from 'https://cardstack.com/base/card-api';
+import { Component } from '@cardstack/base/card-api';
 export class TestCard extends Animal {
   static displayName = "Test Card";
 }`.trim(),
diff --git a/packages/host/tests/acceptance/code-submode/editor-test.ts b/packages/host/tests/acceptance/code-submode/editor-test.ts
index 55a7faf1cd8..81258872cd5 100644
--- a/packages/host/tests/acceptance/code-submode/editor-test.ts
+++ b/packages/host/tests/acceptance/code-submode/editor-test.ts
@@ -262,7 +262,7 @@ module('Acceptance | code submode | editor tests', function (hooks) {
               attributes: {},
               meta: {
                 adoptsFrom: {
-                  module: 'https://cardstack.com/base/cards-grid',
+                  module: '@cardstack/base/cards-grid',
                   name: 'CardsGrid',
                 },
               },
@@ -303,7 +303,7 @@ module('Acceptance | code submode | editor tests', function (hooks) {
               meta: {
                 adoptsFrom: {
                   name: 'Theme',
-                  module: 'https://cardstack.com/base/card-api',
+                  module: '@cardstack/base/card-api',
                 },
               },
               attributes: {
diff --git a/packages/host/tests/acceptance/code-submode/field-playground-test.gts b/packages/host/tests/acceptance/code-submode/field-playground-test.gts
index df80434a2a4..c4a76b12b1f 100644
--- a/packages/host/tests/acceptance/code-submode/field-playground-test.gts
+++ b/packages/host/tests/acceptance/code-submode/field-playground-test.gts
@@ -245,7 +245,7 @@ const commentSpec2 = {
         ],
       },
       adoptsFrom: {
-        module: 'https://cardstack.com/base/spec',
+        module: '@cardstack/base/spec',
         name: 'Spec',
       },
     },
@@ -293,7 +293,7 @@ const commentSpec1 = {
         ],
       },
       adoptsFrom: {
-        module: 'https://cardstack.com/base/spec',
+        module: '@cardstack/base/spec',
         name: 'Spec',
       },
     },
@@ -385,7 +385,7 @@ module('Acceptance | code-submode | field playground', function (_hooks) {
                 },
                 meta: {
                   adoptsFrom: {
-                    module: 'https://cardstack.com/base/spec',
+                    module: '@cardstack/base/spec',
                     name: 'Spec',
                   },
                 },
@@ -431,7 +431,7 @@ module('Acceptance | code-submode | field playground', function (_hooks) {
                     ],
                   },
                   adoptsFrom: {
-                    module: 'https://cardstack.com/base/spec',
+                    module: '@cardstack/base/spec',
                     name: 'Spec',
                   },
                 },
@@ -470,7 +470,7 @@ module('Acceptance | code-submode | field playground', function (_hooks) {
                     ],
                   },
                   adoptsFrom: {
-                    module: 'https://cardstack.com/base/spec',
+                    module: '@cardstack/base/spec',
                     name: 'Spec',
                   },
                 },
@@ -1170,7 +1170,7 @@ module('Acceptance | code-submode | field playground', function (_hooks) {
                     ],
                   },
                   adoptsFrom: {
-                    module: 'https://cardstack.com/base/spec',
+                    module: '@cardstack/base/spec',
                     name: 'Spec',
                   },
                 },
@@ -1190,7 +1190,7 @@ module('Acceptance | code-submode | field playground', function (_hooks) {
                 },
                 meta: {
                   adoptsFrom: {
-                    module: 'https://cardstack.com/base/spec',
+                    module: '@cardstack/base/spec',
                     name: 'Spec',
                   },
                 },
diff --git a/packages/host/tests/acceptance/code-submode/file-tree-test.ts b/packages/host/tests/acceptance/code-submode/file-tree-test.ts
index 918202cd89a..6ab85f1f29a 100644
--- a/packages/host/tests/acceptance/code-submode/file-tree-test.ts
+++ b/packages/host/tests/acceptance/code-submode/file-tree-test.ts
@@ -13,7 +13,7 @@ import { getService } from '@universal-ember/test-support';
 import window from 'ember-window-mock';
 import { module, test } from 'qunit';
 
-import { baseRealm } from '@cardstack/runtime-common';
+import { baseRealmRRI } from '@cardstack/runtime-common';
 
 import WriteTextFileCommand from '@cardstack/host/commands/write-text-file';
 import { ScrollPositions } from '@cardstack/host/utils/local-storage-keys';
@@ -260,7 +260,7 @@ module('Acceptance | code submode | file-tree tests', function (hooks) {
               },
               meta: {
                 adoptsFrom: {
-                  module: `${baseRealm.url}spec`,
+                  module: `${baseRealmRRI}spec`,
                   name: 'Spec',
                 },
               },
diff --git a/packages/host/tests/acceptance/code-submode/inspector-test.ts b/packages/host/tests/acceptance/code-submode/inspector-test.ts
index f7c0f42954c..8f857c62024 100644
--- a/packages/host/tests/acceptance/code-submode/inspector-test.ts
+++ b/packages/host/tests/acceptance/code-submode/inspector-test.ts
@@ -18,7 +18,7 @@ import { module, test } from 'qunit';
 import stringify from 'safe-stable-stringify';
 
 import {
-  baseRealm,
+  baseRealmRRI,
   Deferred,
   type Realm,
   type ResolvedCodeRef,
@@ -77,7 +77,7 @@ const realmAFiles: Record<string, any> = {
       attributes: {},
       meta: {
         adoptsFrom: {
-          module: 'https://cardstack.com/base/cards-grid',
+          module: '@cardstack/base/cards-grid',
           name: 'CardsGrid',
         },
       },
@@ -86,7 +86,7 @@ const realmAFiles: Record<string, any> = {
 };
 
 const indexCardSource = `
-  import { CardDef, Component } from "https://cardstack.com/base/card-api";
+  import { CardDef, Component } from "@cardstack/base/card-api";
 
   export class Index extends CardDef {
     static isolated = class Isolated extends Component<typeof this> {
@@ -100,8 +100,8 @@ const indexCardSource = `
 `;
 
 const personCardSource = `
-  import { contains, containsMany, field, linksToMany, CardDef, Component } from "https://cardstack.com/base/card-api";
-  import StringField from "https://cardstack.com/base/string";
+  import { contains, containsMany, field, linksToMany, CardDef, Component } from "@cardstack/base/card-api";
+  import StringField from "@cardstack/base/string";
   import { Friend } from './friend';
 
   export class Person extends CardDef {
@@ -135,8 +135,8 @@ const personCardSource = `
   }
 `;
 const petCardSource = `
-  import { contains, field, Component, CardDef } from "https://cardstack.com/base/card-api";
-  import StringField from "https://cardstack.com/base/string";
+  import { contains, field, Component, CardDef } from "@cardstack/base/card-api";
+  import StringField from "@cardstack/base/string";
 
   export class Pet extends CardDef {
     static displayName = 'Pet';
@@ -161,8 +161,8 @@ const employeeCardSource = `
     contains,
     field,
     Component,
-  } from 'https://cardstack.com/base/card-api';
-  import StringField from 'https://cardstack.com/base/string';
+  } from '@cardstack/base/card-api';
+  import StringField from '@cardstack/base/string';
   import { Person } from './person';
 
   export class Employee extends Person {
@@ -189,7 +189,7 @@ const erroringModuleSource = `throw new Error('boom');`;
 // identical for both failure modes.
 const brokenThenFixedSource = `throw new Error('initial broken module');`;
 const brokenThenFixedValidSource = `
-  import { CardDef } from 'https://cardstack.com/base/card-api';
+  import { CardDef } from '@cardstack/base/card-api';
   export class BrokenThenFixed extends CardDef {
     static displayName = 'Broken Then Fixed';
   }
@@ -201,8 +201,8 @@ const inThisFileSource = `
     field,
     CardDef,
     FieldDef,
-  } from 'https://cardstack.com/base/card-api';
-  import StringField from 'https://cardstack.com/base/string';
+  } from '@cardstack/base/card-api';
+  import StringField from '@cardstack/base/string';
 
   export const exportedVar = 'exported var';
 
@@ -277,8 +277,8 @@ const componentModuleSource = `
 `;
 
 const friendCardSource = `
-  import { contains, linksTo, field, CardDef, Component } from "https://cardstack.com/base/card-api";
-  import StringField from "https://cardstack.com/base/string";
+  import { contains, linksTo, field, CardDef, Component } from "@cardstack/base/card-api";
+  import StringField from "@cardstack/base/string";
 
   export class Friend extends CardDef {
     static displayName = 'Friend';
@@ -313,8 +313,8 @@ const exportsSource = `
     field,
     CardDef,
     FieldDef
-  } from 'https://cardstack.com/base/card-api';
-  import StringField from 'https://cardstack.com/base/string';
+  } from '@cardstack/base/card-api';
+  import StringField from '@cardstack/base/string';
 
   export class AncestorCard1 extends CardDef {
     static displayName = 'AncestorCard1';
@@ -341,8 +341,8 @@ const specialExportsSource = `
     contains,
     field,
     CardDef
-  } from 'https://cardstack.com/base/card-api';
-  import StringField from 'https://cardstack.com/base/string';
+  } from '@cardstack/base/card-api';
+  import StringField from '@cardstack/base/string';
 
   class AncestorCard extends CardDef {
     static displayName = 'Ancestor';
@@ -367,7 +367,7 @@ const importsSource = `
     field,
     linksTo,
     linksToMany
-  } from 'https://cardstack.com/base/card-api';
+  } from '@cardstack/base/card-api';
 
   export class ChildCard1 extends AncestorCard2 {
     static displayName = 'ChildCard1';
@@ -404,9 +404,9 @@ const reExportSource = `
     FieldDef,
     BaseDef as BDef,
     contains,
-  } from 'https://cardstack.com/base/card-api';
-  import StringField from 'https://cardstack.com/base/string';
-  import NumberField from 'https://cardstack.com/base/number';
+  } from '@cardstack/base/card-api';
+  import StringField from '@cardstack/base/string';
+  import NumberField from '@cardstack/base/number';
 
   export const exportedVar = 'exported var';
 
@@ -419,16 +419,16 @@ const reExportSource = `
   export default NumberField;
   export { Person as Human } from './person';
 
-  export { default as Date } from 'https://cardstack.com/base/date';
+  export { default as Date } from '@cardstack/base/date';
 `;
 
 const fileDefSource = `
-  import { FileDef } from 'https://cardstack.com/base/file-api';
+  import { FileDef } from '@cardstack/base/file-api';
   import {
     contains,
     field,
-  } from 'https://cardstack.com/base/card-api';
-  import StringField from 'https://cardstack.com/base/string';
+  } from '@cardstack/base/card-api';
+  import StringField from '@cardstack/base/string';
 
   export class CustomFileDef extends FileDef {
     static displayName = 'custom file';
@@ -437,7 +437,7 @@ const fileDefSource = `
 `;
 
 const pngDefModuleSource = `
-  export { PngDef } from 'https://cardstack.com/base/png-image-def';
+  export { PngDef } from '@cardstack/base/png-image-def';
 `;
 
 const localInheritSource = `
@@ -446,7 +446,7 @@ const localInheritSource = `
     field,
     CardDef,
     FieldDef,
-  } from 'https://cardstack.com/base/card-api';
+  } from '@cardstack/base/card-api';
 
   class GrandParent extends CardDef {
     static displayName = 'local grandparent';
@@ -551,7 +551,7 @@ module('Acceptance | code submode | inspector tests', function (hooks) {
               },
               meta: {
                 adoptsFrom: {
-                  module: `${baseRealm.url}spec`,
+                  module: `${baseRealmRRI}spec`,
                   name: 'Spec',
                 },
               },
@@ -2082,7 +2082,7 @@ module('Acceptance | code submode | inspector tests', function (hooks) {
     assert.expect(11);
     let expectedSrc = `
 import { ExportedCard } from './in-this-file';
-import { Component } from 'https://cardstack.com/base/card-api';
+import { Component } from '@cardstack/base/card-api';
 export class TestCard extends ExportedCard {
   static displayName = "Test Card";
 }`.trim();
@@ -2191,7 +2191,7 @@ export class TestCard extends ExportedCard {
         content,
         `
 import { ExportedField } from './in-this-file';
-import { Component } from 'https://cardstack.com/base/card-api';
+import { Component } from '@cardstack/base/card-api';
 export class TestField extends ExportedField {
   static displayName = "Test Field";
 }`.trim(),
@@ -2296,7 +2296,7 @@ export class TestFileDef extends CustomFileDef {
     assert.expect(4);
     let expectedSrc = `
 import { ExportedCard as ExportedCardParent } from './in-this-file';
-import { Component } from 'https://cardstack.com/base/card-api';
+import { Component } from '@cardstack/base/card-api';
 export class ExportedCard extends ExportedCardParent {
   static displayName = "Exported Card";
 }`.trim();
diff --git a/packages/host/tests/acceptance/code-submode/recent-files-test.ts b/packages/host/tests/acceptance/code-submode/recent-files-test.ts
index bfba8741e4b..1a170cb30f5 100644
--- a/packages/host/tests/acceptance/code-submode/recent-files-test.ts
+++ b/packages/host/tests/acceptance/code-submode/recent-files-test.ts
@@ -13,7 +13,7 @@ import { getService } from '@universal-ember/test-support';
 import * as MonacoSDK from 'monaco-editor';
 import { module, test } from 'qunit';
 
-import { baseRealm } from '@cardstack/runtime-common';
+import { baseRealm, baseRealmRRI } from '@cardstack/runtime-common';
 
 import type MonacoService from '@cardstack/host/services/monaco-service';
 
@@ -242,7 +242,7 @@ module('Acceptance | code submode | recent files tests', function (hooks) {
               },
               meta: {
                 adoptsFrom: {
-                  module: `${baseRealm.url}spec`,
+                  module: `${baseRealmRRI}spec`,
                   name: 'Spec',
                 },
               },
diff --git a/packages/host/tests/acceptance/code-submode/schema-editor-test.ts b/packages/host/tests/acceptance/code-submode/schema-editor-test.ts
index 8faa16418b6..593083fdc24 100644
--- a/packages/host/tests/acceptance/code-submode/schema-editor-test.ts
+++ b/packages/host/tests/acceptance/code-submode/schema-editor-test.ts
@@ -10,7 +10,7 @@ import { getService } from '@universal-ember/test-support';
 
 import { module, test } from 'qunit';
 
-import { baseRealm, Deferred } from '@cardstack/runtime-common';
+import { baseRealm, baseRealmRRI, Deferred } from '@cardstack/runtime-common';
 
 import type MonacoService from '@cardstack/host/services/monaco-service';
 
@@ -333,7 +333,7 @@ module('Acceptance | code submode | schema editor tests', function (hooks) {
               },
               meta: {
                 adoptsFrom: {
-                  module: `${baseRealm.url}spec`,
+                  module: `${baseRealmRRI}spec`,
                   name: 'Spec',
                 },
               },
@@ -347,13 +347,13 @@ module('Acceptance | code submode | schema editor tests', function (hooks) {
                 cardDescription: 'A field that captures big int values',
                 specType: 'field',
                 ref: {
-                  module: `${baseRealm.url}big-integer`,
+                  module: `${baseRealmRRI}big-integer`,
                   name: 'default',
                 },
               },
               meta: {
                 adoptsFrom: {
-                  module: `${baseRealm.url}spec`,
+                  module: `${baseRealmRRI}spec`,
                   name: 'Spec',
                 },
               },
@@ -367,13 +367,13 @@ module('Acceptance | code submode | schema editor tests', function (hooks) {
                 cardDescription: 'A field that captures date values',
                 specType: 'field',
                 ref: {
-                  module: `${baseRealm.url}date`,
+                  module: `${baseRealmRRI}date`,
                   name: 'default',
                 },
               },
               meta: {
                 adoptsFrom: {
-                  module: `${baseRealm.url}spec`,
+                  module: `${baseRealmRRI}spec`,
                   name: 'Spec',
                 },
               },
@@ -1206,7 +1206,7 @@ module('Acceptance | code submode | schema editor tests', function (hooks) {
     await waitFor('[data-test-tooltip-content]');
     assert
       .dom('[data-test-tooltip-content]')
-      .hasText('https://cardstack.com/base/card-api (BaseDef)');
+      .hasText('@cardstack/base/card-api (BaseDef)');
 
     await triggerEvent(
       '[data-test-card-schema="Base"] [data-test-card-schema-navigational-button]',
diff --git a/packages/host/tests/acceptance/code-submode/spec-test.gts b/packages/host/tests/acceptance/code-submode/spec-test.gts
index 2d7326eb0da..f64095eb448 100644
--- a/packages/host/tests/acceptance/code-submode/spec-test.gts
+++ b/packages/host/tests/acceptance/code-submode/spec-test.gts
@@ -10,7 +10,7 @@ import {
 import { getService } from '@universal-ember/test-support';
 import { module, skip, test } from 'qunit';
 
-import { baseRealm, Deferred, rri } from '@cardstack/runtime-common';
+import { baseRealmRRI, Deferred, rri } from '@cardstack/runtime-common';
 
 import {
   setupLocalIndexing,
@@ -334,7 +334,7 @@ module('Acceptance | Spec preview', function (hooks) {
               },
               meta: {
                 adoptsFrom: {
-                  module: `${baseRealm.url}spec`,
+                  module: `${baseRealmRRI}spec`,
                   name: 'Spec',
                 },
               },
@@ -368,7 +368,7 @@ module('Acceptance | Spec preview', function (hooks) {
                   ],
                 },
                 adoptsFrom: {
-                  module: `${baseRealm.url}spec`,
+                  module: `${baseRealmRRI}spec`,
                   name: 'Spec',
                 },
               },
@@ -386,7 +386,7 @@ module('Acceptance | Spec preview', function (hooks) {
               },
               meta: {
                 adoptsFrom: {
-                  module: `${baseRealm.url}spec`,
+                  module: `${baseRealmRRI}spec`,
                   name: 'Spec',
                 },
               },
@@ -405,7 +405,7 @@ module('Acceptance | Spec preview', function (hooks) {
               },
               meta: {
                 adoptsFrom: {
-                  module: `${baseRealm.url}spec`,
+                  module: `${baseRealmRRI}spec`,
                   name: 'Spec',
                 },
               },
@@ -436,7 +436,7 @@ module('Acceptance | Spec preview', function (hooks) {
               },
               meta: {
                 adoptsFrom: {
-                  module: `${baseRealm.url}spec`,
+                  module: `${baseRealmRRI}spec`,
                   name: 'Spec',
                 },
               },
@@ -536,7 +536,7 @@ module('Acceptance | Spec preview', function (hooks) {
               },
               meta: {
                 adoptsFrom: {
-                  module: `${baseRealm.url}spec`,
+                  module: `${baseRealmRRI}spec`,
                   name: 'Spec',
                 },
               },
@@ -556,7 +556,7 @@ module('Acceptance | Spec preview', function (hooks) {
               },
               meta: {
                 adoptsFrom: {
-                  module: `${baseRealm.url}spec`,
+                  module: `${baseRealmRRI}spec`,
                   name: 'Spec',
                 },
               },
@@ -576,7 +576,7 @@ module('Acceptance | Spec preview', function (hooks) {
               },
               meta: {
                 adoptsFrom: {
-                  module: `${baseRealm.url}spec`,
+                  module: `${baseRealmRRI}spec`,
                   name: 'Spec',
                 },
               },
@@ -596,7 +596,7 @@ module('Acceptance | Spec preview', function (hooks) {
               },
               meta: {
                 adoptsFrom: {
-                  module: `${baseRealm.url}spec`,
+                  module: `${baseRealmRRI}spec`,
                   name: 'Spec',
                 },
               },
@@ -616,7 +616,7 @@ module('Acceptance | Spec preview', function (hooks) {
               },
               meta: {
                 adoptsFrom: {
-                  module: `${baseRealm.url}spec`,
+                  module: `${baseRealmRRI}spec`,
                   name: 'Spec',
                 },
               },
@@ -652,7 +652,7 @@ module('Acceptance | Spec preview', function (hooks) {
               },
               meta: {
                 adoptsFrom: {
-                  module: `${baseRealm.url}spec`,
+                  module: `${baseRealmRRI}spec`,
                   name: 'Spec',
                 },
               },
@@ -686,7 +686,7 @@ module('Acceptance | Spec preview', function (hooks) {
                   ],
                 },
                 adoptsFrom: {
-                  module: `${baseRealm.url}spec`,
+                  module: `${baseRealmRRI}spec`,
                   name: 'Spec',
                 },
               },
diff --git a/packages/host/tests/acceptance/csv-file-def-test.gts b/packages/host/tests/acceptance/csv-file-def-test.gts
index 34406fa17c1..49ecd0a2204 100644
--- a/packages/host/tests/acceptance/csv-file-def-test.gts
+++ b/packages/host/tests/acceptance/csv-file-def-test.gts
@@ -5,7 +5,7 @@ import { getService } from '@universal-ember/test-support';
 import { module, test } from 'qunit';
 
 import {
-  baseRealm,
+  baseRealmRRI,
   type FileExtractResponse,
   type RenderRouteOptions,
   type ResolvedCodeRef,
@@ -51,7 +51,7 @@ module('Acceptance | csv file def', function (hooks) {
   const makeFileURL = (path: string) => new URL(path, testRealmURL).href;
 
   const csvDefCodeRef = (): ResolvedCodeRef => ({
-    module: `${baseRealm.url}csv-file-def` as RealmResourceIdentifier,
+    module: `${baseRealmRRI}csv-file-def` as RealmResourceIdentifier,
     name: 'CsvFileDef',
   });
 
diff --git a/packages/host/tests/acceptance/gts-file-def-test.gts b/packages/host/tests/acceptance/gts-file-def-test.gts
index 16d493d274d..5444b9271fa 100644
--- a/packages/host/tests/acceptance/gts-file-def-test.gts
+++ b/packages/host/tests/acceptance/gts-file-def-test.gts
@@ -5,7 +5,7 @@ import { getService } from '@universal-ember/test-support';
 import { module, test } from 'qunit';
 
 import {
-  baseRealm,
+  baseRealmRRI,
   type FileExtractResponse,
   type RenderRouteOptions,
   type ResolvedCodeRef,
@@ -51,7 +51,7 @@ module('Acceptance | gts file def', function (hooks) {
   const makeFileURL = (path: string) => new URL(path, testRealmURL).href;
 
   const gtsDefCodeRef = (): ResolvedCodeRef => ({
-    module: `${baseRealm.url}gts-file-def` as RealmResourceIdentifier,
+    module: `${baseRealmRRI}gts-file-def` as RealmResourceIdentifier,
     name: 'GtsFileDef',
   });
 
diff --git a/packages/host/tests/acceptance/host-mode-test.gts b/packages/host/tests/acceptance/host-mode-test.gts
index 5a2db2ff498..b0a6320a3b2 100644
--- a/packages/host/tests/acceptance/host-mode-test.gts
+++ b/packages/host/tests/acceptance/host-mode-test.gts
@@ -323,7 +323,7 @@ module('Acceptance | host mode tests', function (hooks) {
             type: 'card',
             meta: {
               adoptsFrom: {
-                module: 'https://cardstack.com/base/cards-grid',
+                module: '@cardstack/base/cards-grid',
                 name: 'CardsGrid',
               },
             },
diff --git a/packages/host/tests/acceptance/image-def/avif-image-def-test.gts b/packages/host/tests/acceptance/image-def/avif-image-def-test.gts
index 4339f183acc..8f6cd091b91 100644
--- a/packages/host/tests/acceptance/image-def/avif-image-def-test.gts
+++ b/packages/host/tests/acceptance/image-def/avif-image-def-test.gts
@@ -5,7 +5,7 @@ import { getService } from '@universal-ember/test-support';
 import { module, test } from 'qunit';
 
 import {
-  baseRealm,
+  baseRealmRRI,
   type FileExtractResponse,
   type RenderRouteOptions,
   type ResolvedCodeRef,
@@ -137,7 +137,7 @@ module('Acceptance | avif image def', function (hooks) {
   const makeFileURL = (path: string) => new URL(path, testRealmURL).href;
 
   const avifDefCodeRef = (): ResolvedCodeRef => ({
-    module: `${baseRealm.url}avif-image-def` as RealmResourceIdentifier,
+    module: `${baseRealmRRI}avif-image-def` as RealmResourceIdentifier,
     name: 'AvifDef',
   });
 
diff --git a/packages/host/tests/acceptance/image-def/gif-image-def-test.gts b/packages/host/tests/acceptance/image-def/gif-image-def-test.gts
index ad9396621de..9c7561dfed9 100644
--- a/packages/host/tests/acceptance/image-def/gif-image-def-test.gts
+++ b/packages/host/tests/acceptance/image-def/gif-image-def-test.gts
@@ -5,7 +5,7 @@ import { getService } from '@universal-ember/test-support';
 import { module, test } from 'qunit';
 
 import {
-  baseRealm,
+  baseRealmRRI,
   type FileExtractResponse,
   type RenderRouteOptions,
   type ResolvedCodeRef,
@@ -103,7 +103,7 @@ module('Acceptance | gif image def', function (hooks) {
   const makeFileURL = (path: string) => new URL(path, testRealmURL).href;
 
   const gifDefCodeRef = (): ResolvedCodeRef => ({
-    module: `${baseRealm.url}gif-image-def` as RealmResourceIdentifier,
+    module: `${baseRealmRRI}gif-image-def` as RealmResourceIdentifier,
     name: 'GifDef',
   });
 
diff --git a/packages/host/tests/acceptance/image-def/jpg-image-def-test.gts b/packages/host/tests/acceptance/image-def/jpg-image-def-test.gts
index 197ac0e9a39..3eca031b7d0 100644
--- a/packages/host/tests/acceptance/image-def/jpg-image-def-test.gts
+++ b/packages/host/tests/acceptance/image-def/jpg-image-def-test.gts
@@ -5,7 +5,7 @@ import { getService } from '@universal-ember/test-support';
 import { module, test } from 'qunit';
 
 import {
-  baseRealm,
+  baseRealmRRI,
   type FileExtractResponse,
   type RenderRouteOptions,
   type ResolvedCodeRef,
@@ -91,7 +91,7 @@ module('Acceptance | jpg image def', function (hooks) {
   const makeFileURL = (path: string) => new URL(path, testRealmURL).href;
 
   const jpgDefCodeRef = (): ResolvedCodeRef => ({
-    module: `${baseRealm.url}jpg-image-def` as RealmResourceIdentifier,
+    module: `${baseRealmRRI}jpg-image-def` as RealmResourceIdentifier,
     name: 'JpgDef',
   });
 
diff --git a/packages/host/tests/acceptance/image-def/png-image-def-test.gts b/packages/host/tests/acceptance/image-def/png-image-def-test.gts
index 22a8193c084..57ec7e3d4e0 100644
--- a/packages/host/tests/acceptance/image-def/png-image-def-test.gts
+++ b/packages/host/tests/acceptance/image-def/png-image-def-test.gts
@@ -5,7 +5,7 @@ import { getService } from '@universal-ember/test-support';
 import { module, test } from 'qunit';
 
 import {
-  baseRealm,
+  baseRealmRRI,
   type FileExtractResponse,
   type RenderRouteOptions,
   type ResolvedCodeRef,
@@ -178,7 +178,7 @@ module('Acceptance | png image def', function (hooks) {
   const makeFileURL = (path: string) => new URL(path, testRealmURL).href;
 
   const pngDefCodeRef = (): ResolvedCodeRef => ({
-    module: `${baseRealm.url}png-image-def` as RealmResourceIdentifier,
+    module: `${baseRealmRRI}png-image-def` as RealmResourceIdentifier,
     name: 'PngDef',
   });
 
diff --git a/packages/host/tests/acceptance/image-def/svg-image-def-test.gts b/packages/host/tests/acceptance/image-def/svg-image-def-test.gts
index 90d577c2d12..6605b4e2f95 100644
--- a/packages/host/tests/acceptance/image-def/svg-image-def-test.gts
+++ b/packages/host/tests/acceptance/image-def/svg-image-def-test.gts
@@ -5,7 +5,7 @@ import { getService } from '@universal-ember/test-support';
 import { module, test } from 'qunit';
 
 import {
-  baseRealm,
+  baseRealmRRI,
   type FileExtractResponse,
   type RenderRouteOptions,
   type ResolvedCodeRef,
@@ -79,7 +79,7 @@ module('Acceptance | svg image def', function (hooks) {
   const makeFileURL = (path: string) => new URL(path, testRealmURL).href;
 
   const svgDefCodeRef = (): ResolvedCodeRef => ({
-    module: `${baseRealm.url}svg-image-def` as RealmResourceIdentifier,
+    module: `${baseRealmRRI}svg-image-def` as RealmResourceIdentifier,
     name: 'SvgDef',
   });
 
diff --git a/packages/host/tests/acceptance/image-def/webp-image-def-test.gts b/packages/host/tests/acceptance/image-def/webp-image-def-test.gts
index 92528596d7c..ba9fab0afac 100644
--- a/packages/host/tests/acceptance/image-def/webp-image-def-test.gts
+++ b/packages/host/tests/acceptance/image-def/webp-image-def-test.gts
@@ -5,7 +5,7 @@ import { getService } from '@universal-ember/test-support';
 import { module, test } from 'qunit';
 
 import {
-  baseRealm,
+  baseRealmRRI,
   type FileExtractResponse,
   type RenderRouteOptions,
   type ResolvedCodeRef,
@@ -96,7 +96,7 @@ module('Acceptance | webp image def', function (hooks) {
   const makeFileURL = (path: string) => new URL(path, testRealmURL).href;
 
   const webpDefCodeRef = (): ResolvedCodeRef => ({
-    module: `${baseRealm.url}webp-image-def` as RealmResourceIdentifier,
+    module: `${baseRealmRRI}webp-image-def` as RealmResourceIdentifier,
     name: 'WebpDef',
   });
 
diff --git a/packages/host/tests/acceptance/interact-submode-creation-and-permissions-test.gts b/packages/host/tests/acceptance/interact-submode-creation-and-permissions-test.gts
index f90e5e67a7b..250be25b247 100644
--- a/packages/host/tests/acceptance/interact-submode-creation-and-permissions-test.gts
+++ b/packages/host/tests/acceptance/interact-submode-creation-and-permissions-test.gts
@@ -917,17 +917,13 @@ module(
           .dom('[data-test-highlights-card-container="ai-app-generator"]')
           .exists();
         assert
-          .dom(
-            '[data-test-card="https://cardstack.com/base/ai-app-generator"] textarea',
-          )
+          .dom('[data-test-card="@cardstack/base/ai-app-generator"] textarea')
           .hasValue(
             'Create a sprint-planning tool that lets users define backlogs, estimate stories, assign owners, and track burndown.',
           );
         await click('[data-test-boxel-button][title="About Me"]');
         assert
-          .dom(
-            '[data-test-card="https://cardstack.com/base/ai-app-generator"] textarea',
-          )
+          .dom('[data-test-card="@cardstack/base/ai-app-generator"] textarea')
           .hasValue(
             'Build a personal portfolio page with your background, skills, and contact information',
           );
@@ -1020,13 +1016,11 @@ module(
           'Design a travel planner dashboard that tracks itineraries, bookings, and budgets';
 
         await fillIn(
-          '[data-test-card="https://cardstack.com/base/ai-app-generator"] textarea',
+          '[data-test-card="@cardstack/base/ai-app-generator"] textarea',
           typedPrompt,
         );
         assert
-          .dom(
-            '[data-test-card="https://cardstack.com/base/ai-app-generator"] textarea',
-          )
+          .dom('[data-test-card="@cardstack/base/ai-app-generator"] textarea')
           .hasValue(typedPrompt);
 
         await click('[data-test-create-this-for-me]');
diff --git a/packages/host/tests/acceptance/interact-submode/create-file-test.gts b/packages/host/tests/acceptance/interact-submode/create-file-test.gts
index da1d2da36fd..6ec859a9217 100644
--- a/packages/host/tests/acceptance/interact-submode/create-file-test.gts
+++ b/packages/host/tests/acceptance/interact-submode/create-file-test.gts
@@ -34,7 +34,7 @@ const testRealmFiles: Record<string, any> = {
     iconURL: 'https://boxel-images.boxel.ai/icons/Letter-t.png',
   }),
   'pet.gts': `
-    import { CardDef, Component } from "https://cardstack.com/base/card-api";
+    import { CardDef, Component } from "@cardstack/base/card-api";
     export default class Pet extends CardDef {
       static displayName = 'Pet';
       static embedded = class Embedded extends Component<typeof this> {
@@ -45,7 +45,7 @@ const testRealmFiles: Record<string, any> = {
     }
   `,
   'person.gts': `
-    import { linksTo, field, CardDef } from "https://cardstack.com/base/card-api";
+    import { linksTo, field, CardDef } from "@cardstack/base/card-api";
     import Pet from "./pet";
     export class Person extends CardDef {
       static displayName = 'Person';
@@ -53,7 +53,7 @@ const testRealmFiles: Record<string, any> = {
     }
   `,
   'author.gts': `
-    import { Component, field, contains, StringField } from 'https://cardstack.com/base/card-api';
+    import { Component, field, contains, StringField } from '@cardstack/base/card-api';
     import { Person } from './person';
     export class Author extends Person {
       static displayName = "Author";
@@ -156,14 +156,14 @@ const userRealmFiles: Record<string, any> = {
     iconURL: 'https://boxel-images.boxel.ai/icons/Letter-a.png',
   }),
   'plant.gts': `
-    import { CardDef, field, contains, StringField } from 'https://cardstack.com/base/card-api';
+    import { CardDef, field, contains, StringField } from '@cardstack/base/card-api';
     export class Plant extends CardDef {
       static displayName = "Plant";
       @field commonName = contains(StringField);
     }
   `,
   'garden.gts': `
-    import { CardDef, field, linksToMany } from 'https://cardstack.com/base/card-api';
+    import { CardDef, field, linksToMany } from '@cardstack/base/card-api';
     import { Plant } from './plant';
     export class Garden extends CardDef {
       static displayName = "Garden";
diff --git a/packages/host/tests/acceptance/json-file-def-test.gts b/packages/host/tests/acceptance/json-file-def-test.gts
index eb698c59510..41276c44421 100644
--- a/packages/host/tests/acceptance/json-file-def-test.gts
+++ b/packages/host/tests/acceptance/json-file-def-test.gts
@@ -5,7 +5,7 @@ import { getService } from '@universal-ember/test-support';
 import { module, test } from 'qunit';
 
 import {
-  baseRealm,
+  baseRealmRRI,
   type FileExtractResponse,
   type RenderRouteOptions,
   type ResolvedCodeRef,
@@ -51,7 +51,7 @@ module('Acceptance | json file def', function (hooks) {
   const makeFileURL = (path: string) => new URL(path, testRealmURL).href;
 
   const jsonFileDefCodeRef = (): ResolvedCodeRef => ({
-    module: `${baseRealm.url}json-file-def` as RealmResourceIdentifier,
+    module: `${baseRealmRRI}json-file-def` as RealmResourceIdentifier,
     name: 'JsonFileDef',
   });
 
diff --git a/packages/host/tests/acceptance/markdown-file-def-test.gts b/packages/host/tests/acceptance/markdown-file-def-test.gts
index 4e91db69b03..e3238c2fd28 100644
--- a/packages/host/tests/acceptance/markdown-file-def-test.gts
+++ b/packages/host/tests/acceptance/markdown-file-def-test.gts
@@ -13,7 +13,7 @@ import { getService } from '@universal-ember/test-support';
 import { module, test } from 'qunit';
 
 import {
-  baseRealm,
+  baseRealmRRI,
   type FileExtractResponse,
   type RenderRouteOptions,
   type ResolvedCodeRef,
@@ -62,7 +62,7 @@ module('Acceptance | markdown file def', function (hooks) {
   const makeFileURL = (path: string) => new URL(path, testRealmURL).href;
 
   const markdownDefCodeRef = (): ResolvedCodeRef => ({
-    module: `${baseRealm.url}markdown-file-def` as RealmResourceIdentifier,
+    module: `${baseRealmRRI}markdown-file-def` as RealmResourceIdentifier,
     name: 'MarkdownDef',
   });
 
diff --git a/packages/host/tests/acceptance/operator-mode-acceptance-test.gts b/packages/host/tests/acceptance/operator-mode-acceptance-test.gts
index 776bc3d9321..7d8d013385d 100644
--- a/packages/host/tests/acceptance/operator-mode-acceptance-test.gts
+++ b/packages/host/tests/acceptance/operator-mode-acceptance-test.gts
@@ -341,7 +341,7 @@ module('Acceptance | operator mode tests', function (hooks) {
             },
             meta: {
               adoptsFrom: {
-                module: 'https://cardstack.com/base/spec',
+                module: '@cardstack/base/spec',
                 name: 'Spec',
               },
             },
@@ -437,7 +437,7 @@ module('Acceptance | operator mode tests', function (hooks) {
             attributes: {},
             meta: {
               adoptsFrom: {
-                module: 'https://cardstack.com/base/cards-grid',
+                module: '@cardstack/base/cards-grid',
                 name: 'CardsGrid',
               },
             },
@@ -448,7 +448,7 @@ module('Acceptance | operator mode tests', function (hooks) {
             type: 'card',
             meta: {
               adoptsFrom: {
-                module: 'https://cardstack.com/base/cards-grid',
+                module: '@cardstack/base/cards-grid',
                 name: 'CardsGrid',
               },
             },
diff --git a/packages/host/tests/acceptance/prerender-meta-test.gts b/packages/host/tests/acceptance/prerender-meta-test.gts
index 872b893091a..d441a0adac3 100644
--- a/packages/host/tests/acceptance/prerender-meta-test.gts
+++ b/packages/host/tests/acceptance/prerender-meta-test.gts
@@ -6,6 +6,7 @@ import { module, test } from 'qunit';
 
 import {
   baseRealm,
+  baseRealmRRI,
   type PrerenderMeta,
   type RenderRouteOptions,
   rri,
@@ -332,7 +333,7 @@ module('Acceptance | prerender | meta', function (hooks) {
       [
         `${testRealmURL}cat/Cat`,
         `${testRealmURL}pet/Pet`,
-        `${baseRealm.url}card-api/CardDef`,
+        `${baseRealmRRI}card-api/CardDef`,
       ],
       'types are correct',
     );
diff --git a/packages/host/tests/acceptance/prerender-module-test.gts b/packages/host/tests/acceptance/prerender-module-test.gts
index 37fb624bde3..7b81193439f 100644
--- a/packages/host/tests/acceptance/prerender-module-test.gts
+++ b/packages/host/tests/acceptance/prerender-module-test.gts
@@ -6,6 +6,7 @@ import { module, test } from 'qunit';
 
 import {
   baseRealm,
+  baseRealmRRI,
   rri,
   trimExecutableExtension,
   type RenderRouteOptions,
@@ -127,7 +128,7 @@ module('Acceptance | prerender | module', function (hooks) {
       'types include the card itself',
     );
     assert.ok(
-      personEntry.types.includes(`${baseRealm.url}card-api/CardDef`),
+      personEntry.types.includes(`${baseRealmRRI}card-api/CardDef`),
       'types include base card',
     );
   });
diff --git a/packages/host/tests/acceptance/text-file-def-test.gts b/packages/host/tests/acceptance/text-file-def-test.gts
index 63f7ccc168a..723223be0b9 100644
--- a/packages/host/tests/acceptance/text-file-def-test.gts
+++ b/packages/host/tests/acceptance/text-file-def-test.gts
@@ -5,7 +5,7 @@ import { getService } from '@universal-ember/test-support';
 import { module, test } from 'qunit';
 
 import {
-  baseRealm,
+  baseRealmRRI,
   type FileExtractResponse,
   type RenderRouteOptions,
   type ResolvedCodeRef,
@@ -51,7 +51,7 @@ module('Acceptance | text file def', function (hooks) {
   const makeFileURL = (path: string) => new URL(path, testRealmURL).href;
 
   const textFileDefCodeRef = (): ResolvedCodeRef => ({
-    module: `${baseRealm.url}text-file-def` as RealmResourceIdentifier,
+    module: `${baseRealmRRI}text-file-def` as RealmResourceIdentifier,
     name: 'TextFileDef',
   });
 
diff --git a/packages/host/tests/acceptance/theme-card-test.gts b/packages/host/tests/acceptance/theme-card-test.gts
index 18eadc69b2d..33174103026 100644
--- a/packages/host/tests/acceptance/theme-card-test.gts
+++ b/packages/host/tests/acceptance/theme-card-test.gts
@@ -249,7 +249,7 @@ module('Acceptance | theme-card-test', function (hooks) {
               meta: {
                 adoptsFrom: {
                   name: 'default',
-                  module: 'https://cardstack.com/base/structured-theme',
+                  module: '@cardstack/base/structured-theme',
                 },
               },
               type: 'card',
@@ -275,7 +275,7 @@ module('Acceptance | theme-card-test', function (hooks) {
               meta: {
                 adoptsFrom: {
                   name: 'default',
-                  module: 'https://cardstack.com/base/style-reference',
+                  module: '@cardstack/base/style-reference',
                 },
               },
               type: 'card',
@@ -322,7 +322,7 @@ module('Acceptance | theme-card-test', function (hooks) {
               meta: {
                 adoptsFrom: {
                   name: 'default',
-                  module: 'https://cardstack.com/base/structured-theme',
+                  module: '@cardstack/base/structured-theme',
                 },
               },
               type: 'card',
@@ -339,7 +339,7 @@ module('Acceptance | theme-card-test', function (hooks) {
               meta: {
                 adoptsFrom: {
                   name: 'default',
-                  module: 'https://cardstack.com/base/structured-theme',
+                  module: '@cardstack/base/structured-theme',
                 },
               },
               type: 'card',
@@ -359,7 +359,7 @@ module('Acceptance | theme-card-test', function (hooks) {
               meta: {
                 adoptsFrom: {
                   name: 'default',
-                  module: 'https://cardstack.com/base/structured-theme',
+                  module: '@cardstack/base/structured-theme',
                 },
               },
               type: 'card',
@@ -379,7 +379,7 @@ module('Acceptance | theme-card-test', function (hooks) {
               meta: {
                 adoptsFrom: {
                   name: 'default',
-                  module: 'https://cardstack.com/base/structured-theme',
+                  module: '@cardstack/base/structured-theme',
                 },
               },
               type: 'card',
diff --git a/packages/host/tests/acceptance/ts-file-def-test.gts b/packages/host/tests/acceptance/ts-file-def-test.gts
index c9ed3315e36..9ffe13364d7 100644
--- a/packages/host/tests/acceptance/ts-file-def-test.gts
+++ b/packages/host/tests/acceptance/ts-file-def-test.gts
@@ -5,7 +5,7 @@ import { getService } from '@universal-ember/test-support';
 import { module, test } from 'qunit';
 
 import {
-  baseRealm,
+  baseRealmRRI,
   type FileExtractResponse,
   type RenderRouteOptions,
   type ResolvedCodeRef,
@@ -51,7 +51,7 @@ module('Acceptance | ts file def', function (hooks) {
   const makeFileURL = (path: string) => new URL(path, testRealmURL).href;
 
   const tsDefCodeRef = (): ResolvedCodeRef => ({
-    module: `${baseRealm.url}ts-file-def` as RealmResourceIdentifier,
+    module: `${baseRealmRRI}ts-file-def` as RealmResourceIdentifier,
     name: 'TsFileDef',
   });
 
diff --git a/packages/host/tests/acceptance/workspace-chooser-delete-test.gts b/packages/host/tests/acceptance/workspace-chooser-delete-test.gts
index 09cba1587af..841cb2299e0 100644
--- a/packages/host/tests/acceptance/workspace-chooser-delete-test.gts
+++ b/packages/host/tests/acceptance/workspace-chooser-delete-test.gts
@@ -57,7 +57,7 @@ module('Acceptance | workspace-chooser-delete', function (hooks) {
             type: 'card',
             meta: {
               adoptsFrom: {
-                module: 'https://cardstack.com/base/cards-grid',
+                module: '@cardstack/base/cards-grid',
                 name: 'CardsGrid',
               },
             },
@@ -68,7 +68,7 @@ module('Acceptance | workspace-chooser-delete', function (hooks) {
             type: 'card',
             meta: {
               adoptsFrom: {
-                module: 'https://cardstack.com/base/card-api',
+                module: '@cardstack/base/card-api',
                 name: 'CardDef',
               },
             },
@@ -95,7 +95,7 @@ export class Person extends CardDef {}
             type: 'card',
             meta: {
               adoptsFrom: {
-                module: 'https://cardstack.com/base/cards-grid',
+                module: '@cardstack/base/cards-grid',
                 name: 'CardsGrid',
               },
             },
@@ -120,7 +120,7 @@ export class Person extends CardDef {}
             type: 'card',
             meta: {
               adoptsFrom: {
-                module: 'https://cardstack.com/base/cards-grid',
+                module: '@cardstack/base/cards-grid',
                 name: 'CardsGrid',
               },
             },
diff --git a/packages/host/tests/acceptance/workspace-chooser-test.gts b/packages/host/tests/acceptance/workspace-chooser-test.gts
index 8f73fb05817..59116c372ed 100644
--- a/packages/host/tests/acceptance/workspace-chooser-test.gts
+++ b/packages/host/tests/acceptance/workspace-chooser-test.gts
@@ -85,7 +85,7 @@ module('Acceptance | workspace-chooser', function (hooks) {
             type: 'card',
             meta: {
               adoptsFrom: {
-                module: 'https://cardstack.com/base/cards-grid',
+                module: '@cardstack/base/cards-grid',
                 name: 'CardsGrid',
               },
             },
@@ -107,7 +107,7 @@ module('Acceptance | workspace-chooser', function (hooks) {
             type: 'card',
             meta: {
               adoptsFrom: {
-                module: 'https://cardstack.com/base/cards-grid',
+                module: '@cardstack/base/cards-grid',
                 name: 'CardsGrid',
               },
             },
diff --git a/packages/host/tests/helpers/index.gts b/packages/host/tests/helpers/index.gts
index a64637a0a24..a6a19763320 100644
--- a/packages/host/tests/helpers/index.gts
+++ b/packages/host/tests/helpers/index.gts
@@ -1021,7 +1021,7 @@ export const SYSTEM_CARD_FIXTURE_CONTENTS: RealmContents = {
       },
       meta: {
         adoptsFrom: {
-          module: 'https://cardstack.com/base/system-card',
+          module: '@cardstack/base/system-card',
           name: 'ModelConfiguration',
         },
       },
@@ -1050,7 +1050,7 @@ export const SYSTEM_CARD_FIXTURE_CONTENTS: RealmContents = {
       },
       meta: {
         adoptsFrom: {
-          module: 'https://cardstack.com/base/system-card',
+          module: '@cardstack/base/system-card',
           name: 'ModelConfiguration',
         },
       },
@@ -1079,7 +1079,7 @@ export const SYSTEM_CARD_FIXTURE_CONTENTS: RealmContents = {
       },
       meta: {
         adoptsFrom: {
-          module: 'https://cardstack.com/base/system-card',
+          module: '@cardstack/base/system-card',
           name: 'ModelConfiguration',
         },
       },
@@ -1108,7 +1108,7 @@ export const SYSTEM_CARD_FIXTURE_CONTENTS: RealmContents = {
       },
       meta: {
         adoptsFrom: {
-          module: 'https://cardstack.com/base/system-card',
+          module: '@cardstack/base/system-card',
           name: 'ModelConfiguration',
         },
       },
@@ -1147,7 +1147,7 @@ export const SYSTEM_CARD_FIXTURE_CONTENTS: RealmContents = {
       },
       meta: {
         adoptsFrom: {
-          module: 'https://cardstack.com/base/system-card',
+          module: '@cardstack/base/system-card',
           name: 'SystemCard',
         },
       },
@@ -2213,7 +2213,7 @@ export function realmConfigCardJSON(
       attributes: attrs,
       meta: {
         adoptsFrom: {
-          module: 'https://cardstack.com/base/realm-config',
+          module: '@cardstack/base/realm-config',
           name: 'RealmConfig',
         },
       },
diff --git a/packages/host/tests/integration/commands/add-field-to-card-definition-command-test.gts b/packages/host/tests/integration/commands/add-field-to-card-definition-command-test.gts
index 489610f2fc7..38b72d3d2ce 100644
--- a/packages/host/tests/integration/commands/add-field-to-card-definition-command-test.gts
+++ b/packages/host/tests/integration/commands/add-field-to-card-definition-command-test.gts
@@ -77,7 +77,7 @@ module(
         fieldName: 'lastName',
         fieldDefinitionType: 'field',
         fieldRef: {
-          module: rri('https://cardstack.com/base/string'),
+          module: rri('@cardstack/base/string'),
           name: 'default',
         },
         fieldType: 'contains',
@@ -116,7 +116,7 @@ module(
         fieldDefinitionType: 'field',
         fieldType: 'contains',
         fieldRef: {
-          module: rri('https://cardstack.com/base/string'),
+          module: rri('@cardstack/base/string'),
           name: 'default',
         },
         incomingRelativeTo: undefined,
diff --git a/packages/host/tests/integration/commands/copy-and-edit-test.gts b/packages/host/tests/integration/commands/copy-and-edit-test.gts
index 7ebf25b6341..4d03bb46a88 100644
--- a/packages/host/tests/integration/commands/copy-and-edit-test.gts
+++ b/packages/host/tests/integration/commands/copy-and-edit-test.gts
@@ -113,7 +113,7 @@ module('Integration | commands | copy-and-edit', function (hooks) {
               },
               meta: {
                 adoptsFrom: {
-                  module: 'https://cardstack.com/base/theme',
+                  module: '@cardstack/base/theme',
                   name: 'default',
                 },
               },
diff --git a/packages/host/tests/integration/commands/copy-card-test.gts b/packages/host/tests/integration/commands/copy-card-test.gts
index f88670eca28..af49c13881c 100644
--- a/packages/host/tests/integration/commands/copy-card-test.gts
+++ b/packages/host/tests/integration/commands/copy-card-test.gts
@@ -72,7 +72,7 @@ module('Integration | commands | copy-card', function (hooks) {
               type: 'card',
               meta: {
                 adoptsFrom: {
-                  module: 'https://cardstack.com/base/cards-grid',
+                  module: '@cardstack/base/cards-grid',
                   name: 'CardsGrid',
                 },
               },
diff --git a/packages/host/tests/integration/commands/store-add-test.gts b/packages/host/tests/integration/commands/store-add-test.gts
index 0723132c5e3..0959bafadf7 100644
--- a/packages/host/tests/integration/commands/store-add-test.gts
+++ b/packages/host/tests/integration/commands/store-add-test.gts
@@ -64,7 +64,7 @@ module('Integration | commands | store-add', function (hooks) {
           attributes: {},
           meta: {
             adoptsFrom: {
-              module: 'https://cardstack.com/base/card-api',
+              module: '@cardstack/base/card-api',
               name: 'CardDef',
             },
           },
diff --git a/packages/host/tests/integration/commands/use-ai-assistant-test.gts b/packages/host/tests/integration/commands/use-ai-assistant-test.gts
index 59dac978ad9..f09520554e0 100644
--- a/packages/host/tests/integration/commands/use-ai-assistant-test.gts
+++ b/packages/host/tests/integration/commands/use-ai-assistant-test.gts
@@ -76,7 +76,7 @@ module('Integration | commands | ai-assistant', function (hooks) {
               },
               meta: {
                 adoptsFrom: {
-                  module: 'https://cardstack.com/base/card-api',
+                  module: '@cardstack/base/card-api',
                   name: 'CardDef',
                 },
               },
@@ -90,7 +90,7 @@ module('Integration | commands | ai-assistant', function (hooks) {
               },
               meta: {
                 adoptsFrom: {
-                  module: 'https://cardstack.com/base/card-api',
+                  module: '@cardstack/base/card-api',
                   name: 'CardDef',
                 },
               },
diff --git a/packages/host/tests/integration/components/ai-assistant-panel/fallback-banner-test.gts b/packages/host/tests/integration/components/ai-assistant-panel/fallback-banner-test.gts
index 6c622a6edde..37f5baee21c 100644
--- a/packages/host/tests/integration/components/ai-assistant-panel/fallback-banner-test.gts
+++ b/packages/host/tests/integration/components/ai-assistant-panel/fallback-banner-test.gts
@@ -42,7 +42,7 @@ const SYSTEM_CARD_CONTENT = {
     attributes: {},
     meta: {
       adoptsFrom: {
-        module: 'https://cardstack.com/base/system-card',
+        module: '@cardstack/base/system-card',
         name: 'SystemCard',
       },
     },
diff --git a/packages/host/tests/integration/components/card-copy-test.gts b/packages/host/tests/integration/components/card-copy-test.gts
index 9f65797fba3..bca911d5d56 100644
--- a/packages/host/tests/integration/components/card-copy-test.gts
+++ b/packages/host/tests/integration/components/card-copy-test.gts
@@ -178,7 +178,7 @@ module('Integration | card-copy', function (hooks) {
             type: 'card',
             meta: {
               adoptsFrom: {
-                module: 'https://cardstack.com/base/cards-grid',
+                module: '@cardstack/base/cards-grid',
                 name: 'CardsGrid',
               },
             },
@@ -253,7 +253,7 @@ module('Integration | card-copy', function (hooks) {
             type: 'card',
             meta: {
               adoptsFrom: {
-                module: 'https://cardstack.com/base/cards-grid',
+                module: '@cardstack/base/cards-grid',
                 name: 'CardsGrid',
               },
             },
@@ -294,7 +294,7 @@ module('Integration | card-copy', function (hooks) {
             type: 'card',
             meta: {
               adoptsFrom: {
-                module: 'https://cardstack.com/base/cards-grid',
+                module: '@cardstack/base/cards-grid',
                 name: 'CardsGrid',
               },
             },
@@ -643,7 +643,7 @@ module('Integration | card-copy', function (hooks) {
             type: 'card',
             meta: {
               adoptsFrom: {
-                module: 'https://cardstack.com/base/cards-grid',
+                module: '@cardstack/base/cards-grid',
                 name: 'CardsGrid',
               },
             },
diff --git a/packages/host/tests/integration/components/card-delete-test.gts b/packages/host/tests/integration/components/card-delete-test.gts
index c13ae45c3ad..d526e6bb00e 100644
--- a/packages/host/tests/integration/components/card-delete-test.gts
+++ b/packages/host/tests/integration/components/card-delete-test.gts
@@ -138,7 +138,7 @@ module('Integration | card-delete', function (hooks) {
             type: 'card',
             meta: {
               adoptsFrom: {
-                module: 'https://cardstack.com/base/cards-grid',
+                module: '@cardstack/base/cards-grid',
                 name: 'CardsGrid',
               },
             },
diff --git a/packages/host/tests/integration/components/field-markdown-specialized-test.gts b/packages/host/tests/integration/components/field-markdown-specialized-test.gts
index 81b7248fa13..2d8f0999c87 100644
--- a/packages/host/tests/integration/components/field-markdown-specialized-test.gts
+++ b/packages/host/tests/integration/components/field-markdown-specialized-test.gts
@@ -430,12 +430,12 @@ module('Integration | field markdown specialized', function (hooks) {
       };
     }
     let card = new Sample({
-      value: { module: 'https://cardstack.com/base/string', name: 'default' },
+      value: { module: '@cardstack/base/string', name: 'default' },
     });
     await renderCard(loader, card, 'isolated');
     assert.strictEqual(
       readMarkdown(this.element),
-      '`https://cardstack.com/base/string/default`',
+      '`@cardstack/base/string/default`',
     );
   });
 
diff --git a/packages/host/tests/integration/components/overlay-menu-items-test.gts b/packages/host/tests/integration/components/overlay-menu-items-test.gts
index db53e43024f..9352d368a9c 100644
--- a/packages/host/tests/integration/components/overlay-menu-items-test.gts
+++ b/packages/host/tests/integration/components/overlay-menu-items-test.gts
@@ -157,7 +157,7 @@ module('Integration | overlay-menu-items', function (hooks) {
             type: 'card',
             meta: {
               adoptsFrom: {
-                module: 'https://cardstack.com/base/cards-grid',
+                module: '@cardstack/base/cards-grid',
                 name: 'CardsGrid',
               },
             },
diff --git a/packages/host/tests/integration/components/serialization-rri-form-audit-test.gts b/packages/host/tests/integration/components/serialization-rri-form-audit-test.gts
new file mode 100644
index 00000000000..c7201e48452
--- /dev/null
+++ b/packages/host/tests/integration/components/serialization-rri-form-audit-test.gts
@@ -0,0 +1,193 @@
+import type { RenderingTestContext } from '@ember/test-helpers';
+
+import { getService } from '@universal-ember/test-support';
+import { module, test } from 'qunit';
+
+import {
+  baseRealm,
+  identifyCard,
+  PermissionsContextName,
+  type Permissions,
+} from '@cardstack/runtime-common';
+import { Loader } from '@cardstack/runtime-common/loader';
+
+import {
+  cardInfo,
+  provideConsumeContext,
+  saveCard,
+  setupCardLogs,
+  setupIntegrationTestRealm,
+  setupLocalIndexing,
+  testRealmURL,
+  testRRI,
+} from '../../helpers';
+import {
+  CardDef,
+  contains,
+  FieldDef,
+  field,
+  linksTo,
+  serializeCard,
+  setupBaseRealm,
+  StringField,
+} from '../../helpers/base-realm';
+import { setupMockMatrix } from '../../helpers/mock-matrix';
+import { setupRenderingTest } from '../../helpers/setup';
+
+let loader: Loader;
+
+module('Integration | serialization | RRI form audit', function (hooks) {
+  setupRenderingTest(hooks);
+  setupBaseRealm(hooks);
+
+  hooks.beforeEach(function (this: RenderingTestContext) {
+    let permissions: Permissions = { canWrite: true, canRead: true };
+    provideConsumeContext(PermissionsContextName, permissions);
+    loader = getService('loader-service').loader;
+  });
+  setupLocalIndexing(hooks);
+
+  let mockMatrixUtils = setupMockMatrix(hooks);
+
+  setupCardLogs(
+    hooks,
+    async () => await loader.import(`${baseRealm.url}card-api`),
+  );
+
+  test('serializeCard output keys against an unmapped (test) realm', async function (assert) {
+    class Author extends FieldDef {
+      @field name = contains(StringField);
+    }
+    class Tag extends CardDef {
+      @field label = contains(StringField);
+    }
+    class Post extends CardDef {
+      @field title = contains(StringField);
+      @field author = contains(Author);
+      @field tag = linksTo(Tag);
+    }
+
+    await setupIntegrationTestRealm({
+      mockMatrixUtils,
+      contents: { 'test-cards.gts': { Author, Post, Tag } },
+    });
+
+    let tag = new Tag({ label: 'announcements' });
+    await saveCard(
+      tag,
+      `${testRealmURL}Tag/announcements`,
+      loader,
+      undefined,
+      testRealmURL,
+    );
+
+    let post = new Post({
+      title: 'Hello',
+      author: new Author({ name: 'Buck' }),
+      tag,
+    });
+    await saveCard(
+      post,
+      `${testRealmURL}Post/1`,
+      loader,
+      undefined,
+      testRealmURL,
+    );
+
+    let doc = serializeCard(post, {
+      includeUnrenderedFields: true,
+      useAbsoluteURL: true,
+    });
+
+    assert.strictEqual(
+      doc.data.id,
+      `${testRealmURL}Post/1`,
+      'data.id is URL form (test realm has no prefix mapping)',
+    );
+    assert.strictEqual(
+      (doc.data.meta as any).realmURL,
+      testRealmURL,
+      'meta.realmURL is URL form (test realm)',
+    );
+    assert.deepEqual(
+      (doc.data.meta as any).adoptsFrom,
+      { module: testRRI('test-cards'), name: 'Post' },
+      'meta.adoptsFrom.module is URL form (test-realm-defined class)',
+    );
+    assert.deepEqual(
+      (doc.data.relationships as any).tag,
+      {
+        links: { self: `${testRealmURL}Tag/announcements` },
+        data: { id: `${testRealmURL}Tag/announcements`, type: 'card' },
+      },
+      'linksTo relationship link.self and data.id are URL form',
+    );
+    assert.deepEqual(
+      doc.data.attributes as any,
+      {
+        title: 'Hello',
+        author: { name: 'Buck' },
+        cardInfo,
+      },
+      'contained FieldDef attributes have no identifier exposure',
+    );
+  });
+
+  test('Loader.identify returns RRI form for base-realm classes', async function (assert) {
+    await setupIntegrationTestRealm({
+      mockMatrixUtils,
+      contents: {},
+    });
+
+    // Base-realm classes (CardDef, FieldDef, etc.) are imported via the
+    // virtual URL `https://cardstack.com/base/...`. `VirtualNetwork.
+    // unresolveURL` chases that through the registered virtual→real URL
+    // mapping and matches the resolved URL against the `@cardstack/base/`
+    // realm-prefix mapping, so the captured module identity comes out in
+    // RRI form.
+    let cardDefRef = Loader.identify(CardDef)!;
+    assert.strictEqual(cardDefRef.name, 'CardDef', 'CardDef name');
+    assert.strictEqual(
+      cardDefRef.module,
+      '@cardstack/base/card-api',
+      'CardDef module is @cardstack/base/ RRI form',
+    );
+
+    let fieldDefRef = Loader.identify(FieldDef)!;
+    assert.strictEqual(fieldDefRef.name, 'FieldDef', 'FieldDef name');
+    assert.strictEqual(
+      fieldDefRef.module,
+      '@cardstack/base/card-api',
+      'FieldDef module is RRI form',
+    );
+
+    // `packages/base/string.ts` is a re-export — `export default StringField`
+    // pointing at the class defined in card-api.gts. The Loader's identity
+    // capture sees card-api first (CardDef et al. are imported together),
+    // so StringField's recorded identity is the card-api named export,
+    // not the string-module default.
+    let stringFieldRef = Loader.identify(StringField)!;
+    assert.strictEqual(stringFieldRef.name, 'StringField', 'StringField name');
+    assert.strictEqual(
+      stringFieldRef.module,
+      '@cardstack/base/card-api',
+      'StringField module is RRI form, pointing at card-api',
+    );
+  });
+
+  test('identifyCard shape for a test-realm-defined class', async function (assert) {
+    class StrField extends FieldDef {
+      @field value = contains(StringField);
+    }
+    await setupIntegrationTestRealm({
+      mockMatrixUtils,
+      contents: { 'test-cards.gts': { StrField } },
+    });
+
+    assert.deepEqual(
+      identifyCard(StrField),
+      { module: testRRI('test-cards'), name: 'StrField' },
+      'A test-realm class identifies to its own URL-form module (no prefix mapping for the test realm)',
+    );
+  });
+});
diff --git a/packages/host/tests/integration/realm-indexing-test.gts b/packages/host/tests/integration/realm-indexing-test.gts
index 20bcdfbde01..88736c78ede 100644
--- a/packages/host/tests/integration/realm-indexing-test.gts
+++ b/packages/host/tests/integration/realm-indexing-test.gts
@@ -7,6 +7,7 @@ import { md5 } from 'super-fast-md5';
 
 import {
   baseRealm,
+  baseRealmRRI,
   baseCardRef,
   internalKeyFor,
   ri,
@@ -110,7 +111,7 @@ module(`Integration | realm indexing`, function (hooks) {
           data: {
             meta: {
               adoptsFrom: {
-                module: 'https://cardstack.com/base/card-api',
+                module: '@cardstack/base/card-api',
                 name: 'CardDef',
               },
             },
@@ -135,7 +136,7 @@ module(`Integration | realm indexing`, function (hooks) {
         },
         meta: {
           adoptsFrom: {
-            module: rri('https://cardstack.com/base/card-api'),
+            module: rri('@cardstack/base/card-api'),
             name: 'CardDef',
           },
           realmURL: ri('http://test-realm/test/'),
@@ -236,7 +237,7 @@ module(`Integration | realm indexing`, function (hooks) {
           data: {
             meta: {
               adoptsFrom: {
-                module: 'https://cardstack.com/base/card-api',
+                module: '@cardstack/base/card-api',
                 name: 'CardDef',
               },
             },
@@ -246,7 +247,7 @@ module(`Integration | realm indexing`, function (hooks) {
           data: {
             meta: {
               adoptsFrom: {
-                module: 'https://cardstack.com/base/card-api',
+                module: '@cardstack/base/card-api',
                 name: 'CardDef',
               },
             },
@@ -286,7 +287,7 @@ module(`Integration | realm indexing`, function (hooks) {
           },
           meta: {
             adoptsFrom: {
-              module: rri('https://cardstack.com/base/card-api'),
+              module: rri('@cardstack/base/card-api'),
               name: 'CardDef',
             },
           },
@@ -1025,7 +1026,7 @@ module(`Integration | realm indexing`, function (hooks) {
             },
             meta: {
               adoptsFrom: {
-                module: 'https://cardstack.com/base/spec',
+                module: '@cardstack/base/spec',
                 name: 'Spec',
               },
             },
@@ -1067,7 +1068,7 @@ module(`Integration | realm indexing`, function (hooks) {
         },
         meta: {
           adoptsFrom: {
-            module: rri('https://cardstack.com/base/spec'),
+            module: rri('@cardstack/base/spec'),
             name: 'Spec',
           },
           lastModified: adapter.lastModifiedMap.get(
@@ -1136,7 +1137,7 @@ module(`Integration | realm indexing`, function (hooks) {
             },
             meta: {
               adoptsFrom: {
-                module: 'https://cardstack.com/base/spec',
+                module: '@cardstack/base/spec',
                 name: 'Spec',
               },
             },
@@ -1196,7 +1197,7 @@ module(`Integration | realm indexing`, function (hooks) {
         },
         meta: {
           adoptsFrom: {
-            module: rri('https://cardstack.com/base/spec'),
+            module: rri('@cardstack/base/spec'),
             name: 'Spec',
           },
           lastModified: adapter.lastModifiedMap.get(
@@ -2028,13 +2029,17 @@ module(`Integration | realm indexing`, function (hooks) {
       undefined,
       getService('network').virtualNetwork,
     );
+    // Compare as a set: the `embedded_html` key order is lexical after
+    // storage round-trip, not semantically meaningful, and the base
+    // CardDef key sorts differently in RRI prefix form (`@cardstack/...`)
+    // than in URL form. Consumers look up by key, never by position.
     assert.deepEqual(
-      Object.keys(embeddedHtml!),
+      [...Object.keys(embeddedHtml!)].sort(),
       [
         `${testRealmURL}fancy-person/FancyPerson`,
         `${testRealmURL}person/Person`,
         cardDefRefURL,
-      ],
+      ].sort(),
       'embedded class hierarchy is correct',
     );
 
@@ -2177,13 +2182,15 @@ module(`Integration | realm indexing`, function (hooks) {
       undefined,
       getService('network').virtualNetwork,
     );
+    // Compare as a set: see the embedded-hierarchy assertion above —
+    // `fitted_html` key order is lexical after storage, not semantic.
     assert.deepEqual(
-      Object.keys(fittedHtml!),
+      [...Object.keys(fittedHtml!)].sort(),
       [
         `${testRealmURL}fancy-person/FancyPerson`,
         `${testRealmURL}person/Person`,
         cardDefRefURL,
-      ],
+      ].sort(),
       'fitted class hierarchy is correct',
     );
 
@@ -2899,7 +2906,7 @@ module(`Integration | realm indexing`, function (hooks) {
             },
             meta: {
               adoptsFrom: {
-                module: 'https://cardstack.com/base/spec',
+                module: '@cardstack/base/spec',
                 name: 'Spec',
               },
             },
@@ -3302,7 +3309,7 @@ module(`Integration | realm indexing`, function (hooks) {
             relationships: {},
             meta: {
               adoptsFrom: {
-                module: 'https://cardstack.com/base/spec',
+                module: '@cardstack/base/spec',
                 name: 'Spec',
               },
             },
@@ -3356,7 +3363,7 @@ module(`Integration | realm indexing`, function (hooks) {
         },
         meta: {
           adoptsFrom: {
-            module: rri('https://cardstack.com/base/spec'),
+            module: rri('@cardstack/base/spec'),
             name: 'Spec',
           },
           lastModified: adapter.lastModifiedMap.get(
@@ -4813,7 +4820,7 @@ module(`Integration | realm indexing`, function (hooks) {
             },
             meta: {
               adoptsFrom: {
-                module: `${baseRealm.url}spec`,
+                module: `${baseRealmRRI}spec`,
                 name: 'Spec',
               },
               fields: {
@@ -5096,7 +5103,7 @@ posts/ignore-me.json
             attributes: {},
             meta: {
               adoptsFrom: {
-                module: 'https://cardstack.com/base/cards-grid',
+                module: '@cardstack/base/cards-grid',
                 name: 'CardsGrid',
               },
             },
@@ -5108,7 +5115,7 @@ posts/ignore-me.json
             attributes: {},
             meta: {
               adoptsFrom: {
-                module: 'https://cardstack.com/base/realm-config',
+                module: '@cardstack/base/realm-config',
                 name: 'RealmConfig',
               },
             },
@@ -5153,7 +5160,7 @@ posts/ignore-me.json
             attributes: {},
             meta: {
               adoptsFrom: {
-                module: 'https://cardstack.com/base/cards-grid',
+                module: '@cardstack/base/cards-grid',
                 name: 'CardsGrid',
               },
             },
@@ -5167,7 +5174,7 @@ posts/ignore-me.json
             },
             meta: {
               adoptsFrom: {
-                module: 'https://cardstack.com/base/realm-config',
+                module: '@cardstack/base/realm-config',
                 name: 'RealmConfig',
               },
             },
diff --git a/packages/host/tests/integration/realm-test.gts b/packages/host/tests/integration/realm-test.gts
index 0b288362be8..cdd8c7f80b3 100644
--- a/packages/host/tests/integration/realm-test.gts
+++ b/packages/host/tests/integration/realm-test.gts
@@ -6,7 +6,7 @@ import { module, test } from 'qunit';
 import { validate as uuidValidate } from 'uuid';
 
 import type { Realm } from '@cardstack/runtime-common';
-import { baseRealm, rri } from '@cardstack/runtime-common';
+import { baseRealm, baseRealmRRI, rri } from '@cardstack/runtime-common';
 import { isSingleCardDocument } from '@cardstack/runtime-common/document-types';
 import {
   cardSrc,
@@ -81,7 +81,7 @@ module('Integration | realm', function (hooks) {
           data: {
             meta: {
               adoptsFrom: {
-                module: 'https://cardstack.com/base/card-api',
+                module: '@cardstack/base/card-api',
                 name: 'CardDef',
               },
             },
@@ -117,7 +117,7 @@ module('Integration | realm', function (hooks) {
         },
         meta: {
           adoptsFrom: {
-            module: 'https://cardstack.com/base/card-api',
+            module: '@cardstack/base/card-api',
             name: 'CardDef',
           },
           lastModified: adapter.lastModifiedMap.get(
@@ -375,7 +375,7 @@ module('Integration | realm', function (hooks) {
           data: {
             meta: {
               adoptsFrom: {
-                module: 'https://cardstack.com/base/card-api',
+                module: '@cardstack/base/card-api',
                 name: 'CardDef',
               },
             },
@@ -444,7 +444,7 @@ module('Integration | realm', function (hooks) {
               type: 'card',
               meta: {
                 adoptsFrom: {
-                  module: 'https://cardstack.com/base/card-api',
+                  module: '@cardstack/base/card-api',
                   name: 'CardDef',
                 },
               },
@@ -520,7 +520,7 @@ module('Integration | realm', function (hooks) {
               type: 'card',
               meta: {
                 adoptsFrom: {
-                  module: 'https://cardstack.com/base/card-api',
+                  module: '@cardstack/base/card-api',
                   name: 'CardDef',
                 },
               },
@@ -556,7 +556,7 @@ module('Integration | realm', function (hooks) {
               type: 'card',
               meta: {
                 adoptsFrom: {
-                  module: 'https://cardstack.com/base/card-api',
+                  module: '@cardstack/base/card-api',
                   name: 'CardDef',
                 },
               },
@@ -2686,7 +2686,7 @@ module('Integration | realm', function (hooks) {
           data: {
             meta: {
               adoptsFrom: {
-                module: 'https://cardstack.com/base/card-api',
+                module: '@cardstack/base/card-api',
                 name: 'CardDef',
               },
             },
@@ -2696,7 +2696,7 @@ module('Integration | realm', function (hooks) {
           data: {
             meta: {
               adoptsFrom: {
-                module: 'https://cardstack.com/base/card-api',
+                module: '@cardstack/base/card-api',
                 name: 'CardDef',
               },
             },
@@ -2996,7 +2996,7 @@ module('Integration | realm', function (hooks) {
             attributes: {},
             meta: {
               adoptsFrom: {
-                module: 'https://cardstack.com/base/card-api',
+                module: '@cardstack/base/card-api',
                 name: 'CardDef',
               },
             },
@@ -3104,7 +3104,7 @@ module('Integration | realm', function (hooks) {
           sort: [
             {
               by: 'id',
-              on: { module: `${baseRealm.url}card-api`, name: 'CardDef' },
+              on: { module: `${baseRealmRRI}card-api`, name: 'CardDef' },
             },
           ],
         }),
@@ -3303,7 +3303,7 @@ module('Integration | realm', function (hooks) {
             attributes: {},
             meta: {
               adoptsFrom: {
-                module: 'https://cardstack.com/base/card-api',
+                module: '@cardstack/base/card-api',
                 name: 'CardDef',
               },
             },
@@ -3546,7 +3546,7 @@ posts/ignore-me.gts
             type: 'card',
             meta: {
               adoptsFrom: {
-                module: 'https://cardstack.com/base/card-api',
+                module: '@cardstack/base/card-api',
                 name: 'FieldDef',
               },
             },
diff --git a/packages/host/tests/integration/store-test.gts b/packages/host/tests/integration/store-test.gts
index 6f0ce169d6b..eaca137d8b0 100644
--- a/packages/host/tests/integration/store-test.gts
+++ b/packages/host/tests/integration/store-test.gts
@@ -1511,7 +1511,7 @@ module('Integration | Store', function (hooks) {
                 },
                 meta: {
                   adoptsFrom: {
-                    module: 'https://cardstack.com/base/card-api',
+                    module: '@cardstack/base/card-api',
                     name: 'FileDef',
                   },
                 },
@@ -1527,7 +1527,7 @@ module('Integration | Store', function (hooks) {
                 },
                 meta: {
                   adoptsFrom: {
-                    module: 'https://cardstack.com/base/card-api',
+                    module: '@cardstack/base/card-api',
                     name: 'FileDef',
                   },
                 },
@@ -1543,7 +1543,7 @@ module('Integration | Store', function (hooks) {
                 },
                 meta: {
                   adoptsFrom: {
-                    module: 'https://cardstack.com/base/card-api',
+                    module: '@cardstack/base/card-api',
                     name: 'FileDef',
                   },
                 },
diff --git a/packages/host/tests/unit/index-query-engine-test.ts b/packages/host/tests/unit/index-query-engine-test.ts
index 8adb63870ee..484dc3cb3ae 100644
--- a/packages/host/tests/unit/index-query-engine-test.ts
+++ b/packages/host/tests/unit/index-query-engine-test.ts
@@ -6,6 +6,7 @@ import {
   Loader,
   VirtualNetwork,
   baseRealm,
+  baseRealmRRI,
   IndexQueryEngine,
   fetcher,
   maybeHandleScopedCSSRequest,
@@ -61,6 +62,7 @@ module('Unit | query', function (hooks) {
       new URL(baseRealm.url),
       new URL(resolvedBaseRealmURL),
     );
+    virtualNetwork.addRealmMapping('@cardstack/base/', resolvedBaseRealmURL);
     virtualNetwork.addImportMap('@cardstack/boxel-icons/', (rest) => {
       return `${ENV.iconsURL}/@cardstack/boxel-icons/v1/icons/${rest}.js`;
     });
@@ -137,14 +139,14 @@ module('Unit | query', function (hooks) {
     let stringFieldEntry = new SimpleSpec({
       cardTitle: 'String Field',
       ref: {
-        module: `${baseRealm.url}string`,
+        module: `${baseRealmRRI}string`,
         name: 'default',
       },
     });
     let numberFieldEntry = new SimpleSpec({
       cardTitle: 'Number Field',
       ref: {
-        module: `${baseRealm.url}number`,
+        module: `${baseRealmRRI}number`,
         name: 'default',
       },
     });
@@ -885,7 +887,7 @@ module('Unit | query', function (hooks) {
           on: type,
           eq: {
             ref: {
-              module: `${baseRealm.url}string`,
+              module: `${baseRealmRRI}string`,
               name: 'default',
             },
           },
diff --git a/packages/host/tests/unit/instance-filter-matcher-test.ts b/packages/host/tests/unit/instance-filter-matcher-test.ts
index 5acff51218a..0c2d7fa2abd 100644
--- a/packages/host/tests/unit/instance-filter-matcher-test.ts
+++ b/packages/host/tests/unit/instance-filter-matcher-test.ts
@@ -40,6 +40,7 @@ module('Unit | instance-filter-matcher', function (hooks) {
       new URL(baseRealm.url),
       new URL(resolvedBaseRealmURL),
     );
+    virtualNetwork.addRealmMapping('@cardstack/base/', resolvedBaseRealmURL);
     virtualNetwork.addImportMap('@cardstack/boxel-icons/', (rest) => {
       return `${ENV.iconsURL}/@cardstack/boxel-icons/v1/icons/${rest}.js`;
     });
diff --git a/packages/host/tests/unit/loader-test.ts b/packages/host/tests/unit/loader-test.ts
index f6c6073c025..644b5bc1b57 100644
--- a/packages/host/tests/unit/loader-test.ts
+++ b/packages/host/tests/unit/loader-test.ts
@@ -353,6 +353,11 @@ module('Unit | loader', function (hooks) {
       default: StringField,
     });
 
+    // This Loader is constructed without a `virtualNetwork`, so
+    // `captureIdentitiesOfModuleExports` records the raw shim module
+    // identifier without running it through `vn.unresolveURL`. The
+    // identity stays in URL form. Other test setups that build a VN
+    // alongside the Loader see the RRI canonical form here.
     assert.deepEqual(Loader.identify(StringField), {
       module: `${baseRealm.url}card-api`,
       name: 'StringField',
diff --git a/packages/matrix/tests/commands.spec.ts b/packages/matrix/tests/commands.spec.ts
index 12b3d92bf84..4d593c56829 100644
--- a/packages/matrix/tests/commands.spec.ts
+++ b/packages/matrix/tests/commands.spec.ts
@@ -48,7 +48,7 @@ test.describe('Commands', () => {
         },
         meta: {
           adoptsFrom: {
-            module: 'https://cardstack.com/base/card-api',
+            module: '@cardstack/base/card-api',
             name: 'CardDef',
           },
         },
@@ -105,7 +105,7 @@ test.describe('Commands', () => {
         },
         meta: {
           adoptsFrom: {
-            module: 'https://cardstack.com/base/card-api',
+            module: '@cardstack/base/card-api',
             name: 'CardDef',
           },
         },
@@ -160,7 +160,7 @@ test.describe('Commands', () => {
         },
         meta: {
           adoptsFrom: {
-            module: 'https://cardstack.com/base/card-api',
+            module: '@cardstack/base/card-api',
             name: 'CardDef',
           },
         },
diff --git a/packages/matrix/tests/correctness-checks.spec.ts b/packages/matrix/tests/correctness-checks.spec.ts
index bd857fca257..97797d0e3d9 100644
--- a/packages/matrix/tests/correctness-checks.spec.ts
+++ b/packages/matrix/tests/correctness-checks.spec.ts
@@ -519,8 +519,8 @@ ${originalContent}
     const modulePath = 'import-check.gts';
     const moduleUrl = `${realmURL}${modulePath}`;
     const originalModuleSource = `
-import { CardDef, field, contains, StringField } from 'https://cardstack.com/base/card-api';
-import { Component } from 'https://cardstack.com/base/card-api';
+import { CardDef, field, contains, StringField } from '@cardstack/base/card-api';
+import { Component } from '@cardstack/base/card-api';
 export class ImportCheck extends CardDef {
   @field title = contains(StringField);
   static isolated = class Isolated extends Component<typeof this> {
@@ -532,8 +532,8 @@ export class ImportCheck extends CardDef {
 `.trim();
     const originalModuleContent = `${originalModuleSource}\n`;
     const brokenModuleContent = originalModuleContent.replace(
-      `https://cardstack.com/base/card-api'`,
-      `https://cardstack.com/base/card-api-broken'`,
+      `@cardstack/base/card-api'`,
+      `@cardstack/base/card-api-broken'`,
     );
 
     await postCardSource(page, realmURL, modulePath, originalModuleContent);
@@ -718,16 +718,16 @@ ${brokenModuleContent}
       failingResult.data.attributes.errors.some(
         (err: string) =>
           err.includes(moduleUrl.replace('.gts', '')) &&
-          err.includes('https://cardstack.com/base/card-api-broken not found'),
+          err.includes('@cardstack/base/card-api-broken not found'),
       ),
     ).toBe(true);
 
     const fixMessageBody = `\`\`\`
 ${moduleUrl}
 ╔═══ SEARCH ════╗
-} from 'https://cardstack.com/base/card-api-broken';
+} from '@cardstack/base/card-api-broken';
 ╠═══════════════╣
-} from 'https://cardstack.com/base/card-api';
+} from '@cardstack/base/card-api';
 ╚═══ REPLACE ═══╝
 \`\`\``;
     await applyPatchMessage(fixMessageBody);
diff --git a/packages/matrix/tests/host-mode.spec.ts b/packages/matrix/tests/host-mode.spec.ts
index 39e55fc3d68..7d9d1e47e7b 100644
--- a/packages/matrix/tests/host-mode.spec.ts
+++ b/packages/matrix/tests/host-mode.spec.ts
@@ -265,7 +265,7 @@ async function createAndPublishHostModeRealm(
           },
           meta: {
             adoptsFrom: {
-              module: 'https://cardstack.com/base/realm-config',
+              module: '@cardstack/base/realm-config',
               name: 'RealmConfig',
             },
           },
diff --git a/packages/matrix/tests/live-cards.spec.ts b/packages/matrix/tests/live-cards.spec.ts
index 07530a5a2b9..bbb4b32782d 100644
--- a/packages/matrix/tests/live-cards.spec.ts
+++ b/packages/matrix/tests/live-cards.spec.ts
@@ -36,7 +36,7 @@ test.describe('Live Cards', () => {
         },
         meta: {
           adoptsFrom: {
-            module: 'https://cardstack.com/base/card-api',
+            module: '@cardstack/base/card-api',
             name: 'CardDef',
           },
         },
@@ -63,7 +63,7 @@ test.describe('Live Cards', () => {
         },
         meta: {
           adoptsFrom: {
-            module: 'https://cardstack.com/base/card-api',
+            module: '@cardstack/base/card-api',
             name: 'CardDef',
           },
         },
@@ -179,7 +179,7 @@ test.describe('Live Cards', () => {
         },
         meta: {
           adoptsFrom: {
-            module: 'https://cardstack.com/base/card-api',
+            module: '@cardstack/base/card-api',
             name: 'CardDef',
           },
         },
diff --git a/packages/realm-server/handlers/create-realm.ts b/packages/realm-server/handlers/create-realm.ts
index ea3d7b3ee93..10e8f2f02ae 100644
--- a/packages/realm-server/handlers/create-realm.ts
+++ b/packages/realm-server/handlers/create-realm.ts
@@ -175,7 +175,7 @@ export async function createRealm(
         },
         meta: {
           adoptsFrom: {
-            module: 'https://cardstack.com/base/realm-config',
+            module: '@cardstack/base/realm-config',
             name: 'RealmConfig',
           },
         },
@@ -186,7 +186,7 @@ export async function createRealm(
         type: 'card',
         meta: {
           adoptsFrom: {
-            module: 'https://cardstack.com/base/cards-grid',
+            module: '@cardstack/base/cards-grid',
             name: 'CardsGrid',
           },
         },
diff --git a/packages/realm-server/main.ts b/packages/realm-server/main.ts
index b8db76c556a..91b9d608e6c 100644
--- a/packages/realm-server/main.ts
+++ b/packages/realm-server/main.ts
@@ -307,6 +307,17 @@ for (let i = 0; i < fromUrls.length; i++) {
     let fromURL = new URL(from);
     virtualNetwork.addURLMapping(fromURL, to);
     urlMappings.push([fromURL, to]);
+    // Convention: https://cardstack.com/X/ aliases @cardstack/X/. Register
+    // the realm-prefix mapping too so unresolveURL on either form
+    // canonicalises to the same RRI form. This matters for cross-process
+    // cache keys (e.g. host prerender writes definitions cache keyed by
+    // internalKeyFor; realm-server reads back with the same VN). Without
+    // this, the realm-server would see only the URL mapping for base and
+    // the host's RRI-form keys would never match.
+    let m = from.match(/^https:\/\/cardstack\.com\/([^/]+)\/$/);
+    if (m) {
+      virtualNetwork.addRealmMapping(`@cardstack/${m[1]}/`, to.href);
+    }
   } else {
     virtualNetwork.addRealmMapping(from, to.href);
     urlMappings.push([to, to]); // use toUrl for both in hrefs
diff --git a/packages/realm-server/tests/card-dependencies-endpoint-test.ts b/packages/realm-server/tests/card-dependencies-endpoint-test.ts
index f5f3bf439e4..19232cda90c 100644
--- a/packages/realm-server/tests/card-dependencies-endpoint-test.ts
+++ b/packages/realm-server/tests/card-dependencies-endpoint-test.ts
@@ -61,7 +61,7 @@ module(basename(__filename), function () {
           let result: string[] = JSON.parse(response.text.trim());
 
           assert.ok(
-            result.includes('https://cardstack.com/base/card-api'),
+            result.includes('@cardstack/base/card-api'),
             'card-api is a dependency',
           );
           assert.false(
@@ -81,7 +81,7 @@ module(basename(__filename), function () {
           let result: string[] = JSON.parse(response.text.trim());
 
           assert.ok(
-            result.includes('https://cardstack.com/base/card-api'),
+            result.includes('@cardstack/base/card-api'),
             'card-api is a dependency',
           );
           assert.false(
diff --git a/packages/realm-server/tests/card-endpoints-test.ts b/packages/realm-server/tests/card-endpoints-test.ts
index 066b4e41b18..1b718f82e2d 100644
--- a/packages/realm-server/tests/card-endpoints-test.ts
+++ b/packages/realm-server/tests/card-endpoints-test.ts
@@ -1281,7 +1281,7 @@ module(basename(__filename), function () {
                 attributes: {},
                 meta: {
                   adoptsFrom: {
-                    module: rri('https://cardstack.com/base/card-api'),
+                    module: rri('@cardstack/base/card-api'),
                     name: 'CardDef',
                   },
                 },
@@ -1346,7 +1346,7 @@ module(basename(__filename), function () {
                 type: 'card',
                 meta: {
                   adoptsFrom: {
-                    module: rri('https://cardstack.com/base/card-api'),
+                    module: rri('@cardstack/base/card-api'),
                     name: 'CardDef',
                   },
                 },
@@ -2331,7 +2331,7 @@ module(basename(__filename), function () {
                 attributes: {},
                 meta: {
                   adoptsFrom: {
-                    module: rri('https://cardstack.com/base/card-api'),
+                    module: rri('@cardstack/base/card-api'),
                     name: 'CardDef',
                   },
                 },
@@ -4336,7 +4336,7 @@ module(basename(__filename), function () {
               attributes: {},
               meta: {
                 adoptsFrom: {
-                  module: rri('https://cardstack.com/base/card-api'),
+                  module: rri('@cardstack/base/card-api'),
                   name: 'CardDef',
                 },
               },
diff --git a/packages/realm-server/tests/definition-lookup-test.ts b/packages/realm-server/tests/definition-lookup-test.ts
index eae3f1f0d56..b7946d53ae9 100644
--- a/packages/realm-server/tests/definition-lookup-test.ts
+++ b/packages/realm-server/tests/definition-lookup-test.ts
@@ -158,7 +158,7 @@ module(basename(__filename), function () {
                       isPrimitive: true,
                       isComputed: false,
                       fieldOrCard: {
-                        module: rri('https://cardstack.com/base/string'),
+                        module: rri('@cardstack/base/string'),
                         name: 'default',
                       },
                       serializerName: undefined,
diff --git a/packages/realm-server/tests/eq-containment-integration-test.ts b/packages/realm-server/tests/eq-containment-integration-test.ts
index 02b7767b61c..04f116b0317 100644
--- a/packages/realm-server/tests/eq-containment-integration-test.ts
+++ b/packages/realm-server/tests/eq-containment-integration-test.ts
@@ -32,9 +32,9 @@ function ref(module: string, name: string): ResolvedCodeRef {
 
 const testRealmURL = 'http://eq-containment-test/';
 
-const stringRef = ref('https://cardstack.com/base/string', 'default');
-const numberRef = ref('https://cardstack.com/base/number', 'default');
-const booleanRef = ref('https://cardstack.com/base/boolean', 'default');
+const stringRef = ref('@cardstack/base/string', 'default');
+const numberRef = ref('@cardstack/base/number', 'default');
+const booleanRef = ref('@cardstack/base/boolean', 'default');
 const policyRef = ref(`${testRealmURL}policy`, 'Policy');
 const customerRef = ref(`${testRealmURL}customer`, 'Customer');
 const metadataRef = ref(`${testRealmURL}policy`, 'Metadata');
diff --git a/packages/realm-server/tests/helpers/index.ts b/packages/realm-server/tests/helpers/index.ts
index 27bdfca4d22..359dec83ffc 100644
--- a/packages/realm-server/tests/helpers/index.ts
+++ b/packages/realm-server/tests/helpers/index.ts
@@ -281,6 +281,11 @@ export function cleanWhiteSpace(text: string) {
 export function createVirtualNetwork() {
   let virtualNetwork = new VirtualNetwork();
   virtualNetwork.addURLMapping(new URL(baseRealm.url), new URL(localBaseRealm));
+  // Mirror the host's network.ts and main.ts symmetry: when the
+  // baseRealm fake URL is registered as a URL alias, also register the
+  // @cardstack/base/ realm-prefix mapping so unresolveURL on either
+  // form canonicalises to the same RRI.
+  virtualNetwork.addRealmMapping('@cardstack/base/', localBaseRealm);
   return virtualNetwork;
 }
 
@@ -2642,6 +2647,11 @@ async function buildBaseRealmTemplate(
       `http://127.0.0.1:${baseRealmTemplateBuilderPort}/base/`,
     );
     virtualNetwork.addURLMapping(new URL(baseRealm.url), localBaseRealmURL);
+    // Mirror the symmetry from createVirtualNetwork: register the
+    // @cardstack/base/ realm-prefix mapping too. unresolveURL on the
+    // virtual base-realm URL needs the prefix mapping to canonicalise
+    // to RRI form, matching what the host-side prerender writes.
+    virtualNetwork.addRealmMapping('@cardstack/base/', localBaseRealmURL.href);
 
     let definitionLookup = new CachingDefinitionLookup(
       dbAdapter,
@@ -2891,7 +2901,7 @@ export function realmConfigCardJSON(
       attributes: attrs,
       meta: {
         adoptsFrom: {
-          module: 'https://cardstack.com/base/realm-config',
+          module: '@cardstack/base/realm-config',
           name: 'RealmConfig',
         },
       },
diff --git a/packages/realm-server/tests/indexing-test.ts b/packages/realm-server/tests/indexing-test.ts
index fee23008028..789847bb846 100644
--- a/packages/realm-server/tests/indexing-test.ts
+++ b/packages/realm-server/tests/indexing-test.ts
@@ -397,7 +397,7 @@ function makeTestRealmFileSystem(): Record<
         attributes: {},
         meta: {
           adoptsFrom: {
-            module: rri('https://cardstack.com/base/card-api'),
+            module: rri('@cardstack/base/card-api'),
             name: 'CardDef',
           },
         },
@@ -1129,7 +1129,7 @@ module(basename(__filename), function () {
         'deps include mismatch extractor module',
       );
       assert.ok(
-        deps.includes('https://cardstack.com/base/file-api'),
+        deps.includes('@cardstack/base/file-api'),
         'deps include base file-api for fallback',
       );
     });
@@ -1165,7 +1165,7 @@ module(basename(__filename), function () {
       assert.deepEqual(
         doc.data.meta?.adoptsFrom,
         {
-          module: rri('https://cardstack.com/base/text-file-def'),
+          module: rri('@cardstack/base/text-file-def'),
           name: 'TextFileDef',
         },
         'adoptsFrom sourced from pristine file resource',
diff --git a/packages/realm-server/tests/lazy-mount-test.ts b/packages/realm-server/tests/lazy-mount-test.ts
index c160dfc149b..30180ebad7a 100644
--- a/packages/realm-server/tests/lazy-mount-test.ts
+++ b/packages/realm-server/tests/lazy-mount-test.ts
@@ -132,7 +132,7 @@ module(basename(__filename), function () {
 
     test('server.start() eager-mounts pinned rows only', async function (assert) {
       await seedRow(dbAdapter, {
-        url: 'https://cardstack.com/base/',
+        url: '@cardstack/base/',
         kind: 'bootstrap',
         disk_id: '/abs/base',
         owner_username: 'system',
@@ -150,7 +150,7 @@ module(basename(__filename), function () {
 
       assert.deepEqual(
         mountCalls,
-        ['https://cardstack.com/base/'],
+        ['@cardstack/base/'],
         'only the pinned bootstrap row was mounted at boot',
       );
       assert.strictEqual(
diff --git a/packages/realm-server/tests/module-cache-invalidation-listener-test.ts b/packages/realm-server/tests/module-cache-invalidation-listener-test.ts
index 64bd536fc0c..a5ecab46282 100644
--- a/packages/realm-server/tests/module-cache-invalidation-listener-test.ts
+++ b/packages/realm-server/tests/module-cache-invalidation-listener-test.ts
@@ -139,21 +139,21 @@ module(basename(__filename), function () {
 
     test('parses a module payload carrying many URLs', function (assert) {
       const urls = [
-        'https://cardstack.com/base/card-api.gts',
-        'https://cardstack.com/base/string.gts',
-        'https://cardstack.com/base/number.gts',
+        '@cardstack/base/card-api.gts',
+        '@cardstack/base/string.gts',
+        '@cardstack/base/number.gts',
       ];
       assert.deepEqual(
         parseModuleCacheInvalidationPayload(
           JSON.stringify({
             k: 'module',
-            r: 'https://cardstack.com/base/',
+            r: '@cardstack/base/',
             m: urls,
           }),
         ),
         {
           kind: 'module',
-          resolvedRealmURL: 'https://cardstack.com/base/',
+          resolvedRealmURL: '@cardstack/base/',
           moduleURLs: urls,
         },
       );
diff --git a/packages/realm-server/tests/module-cache-race-test.ts b/packages/realm-server/tests/module-cache-race-test.ts
index 2f07a171051..c36d87c0077 100644
--- a/packages/realm-server/tests/module-cache-race-test.ts
+++ b/packages/realm-server/tests/module-cache-race-test.ts
@@ -1277,7 +1277,7 @@ module(basename(__filename), function () {
             attributes: { cardInfo: { name: 'Peer Realm' } },
             meta: {
               adoptsFrom: {
-                module: 'https://cardstack.com/base/realm-config',
+                module: '@cardstack/base/realm-config',
                 name: 'RealmConfig',
               },
             },
@@ -1744,7 +1744,7 @@ module(basename(__filename), function () {
             attributes: { cardInfo: { name: 'Startup Realm' } },
             meta: {
               adoptsFrom: {
-                module: 'https://cardstack.com/base/realm-config',
+                module: '@cardstack/base/realm-config',
                 name: 'RealmConfig',
               },
             },
diff --git a/packages/realm-server/tests/module-syntax-test.ts b/packages/realm-server/tests/module-syntax-test.ts
index 3bed9675528..27a4db8896f 100644
--- a/packages/realm-server/tests/module-syntax-test.ts
+++ b/packages/realm-server/tests/module-syntax-test.ts
@@ -37,7 +37,7 @@ module(basename(__filename), function () {
         },
         fieldName: 'age',
         fieldRef: {
-          module: rri('https://cardstack.com/base/number'),
+          module: rri('@cardstack/base/number'),
           name: 'default',
         },
         fieldType: 'contains',
@@ -122,7 +122,7 @@ module(basename(__filename), function () {
         field?.card,
         {
           type: 'external',
-          module: 'https://cardstack.com/base/number',
+          module: '@cardstack/base/number',
           name: 'default',
         },
         'the field card is correct',
@@ -131,7 +131,7 @@ module(basename(__filename), function () {
         field?.type,
         {
           type: 'external',
-          module: 'https://cardstack.com/base/card-api',
+          module: '@cardstack/base/card-api',
           name: 'contains',
         },
         'the field type is correct',
@@ -140,7 +140,7 @@ module(basename(__filename), function () {
         field?.decorator,
         {
           type: 'external',
-          module: 'https://cardstack.com/base/card-api',
+          module: '@cardstack/base/card-api',
           name: 'field',
         },
         'the field decorator is correct',
@@ -155,7 +155,7 @@ module(basename(__filename), function () {
         },
         fieldName: 'lastName',
         fieldRef: {
-          module: rri('https://cardstack.com/base/string'),
+          module: rri('@cardstack/base/string'),
           name: 'default',
         },
         fieldType: 'contains',
@@ -538,7 +538,7 @@ module(basename(__filename), function () {
         },
         fieldName: 'firstName',
         fieldRef: {
-          module: rri('https://cardstack.com/base/string'),
+          module: rri('@cardstack/base/string'),
           name: 'default',
         },
         fieldType: 'contains',
@@ -596,7 +596,7 @@ module(basename(__filename), function () {
         fieldName: 'age',
         fieldDefinitionType: 'field',
         fieldRef: {
-          module: rri('https://cardstack.com/base/number'),
+          module: rri('@cardstack/base/number'),
           name: 'default',
         },
         fieldType: 'contains',
@@ -661,7 +661,7 @@ module(basename(__filename), function () {
         fieldName: 'age',
         fieldDefinitionType: 'field',
         fieldRef: {
-          module: rri('https://cardstack.com/base/number'),
+          module: rri('@cardstack/base/number'),
           name: 'default',
         },
         fieldType: 'contains',
@@ -729,7 +729,7 @@ module(basename(__filename), function () {
         fieldName: 'age',
         fieldDefinitionType: 'field',
         fieldRef: {
-          module: rri('https://cardstack.com/base/number'),
+          module: rri('@cardstack/base/number'),
           name: 'default',
         },
         fieldType: 'contains',
@@ -789,7 +789,7 @@ module(basename(__filename), function () {
         fieldName: 'aliases',
         fieldDefinitionType: 'field',
         fieldRef: {
-          module: rri('https://cardstack.com/base/string'),
+          module: rri('@cardstack/base/string'),
           name: 'default',
         },
         fieldType: 'containsMany',
@@ -822,7 +822,7 @@ module(basename(__filename), function () {
         field?.type,
         {
           type: 'external',
-          module: 'https://cardstack.com/base/card-api',
+          module: '@cardstack/base/card-api',
           name: 'containsMany',
         },
         'the field type is correct',
@@ -880,7 +880,7 @@ module(basename(__filename), function () {
         field?.type,
         {
           type: 'external',
-          module: 'https://cardstack.com/base/card-api',
+          module: '@cardstack/base/card-api',
           name: 'linksTo',
         },
         'the field type is correct',
@@ -939,7 +939,7 @@ module(basename(__filename), function () {
         field?.type,
         {
           type: 'external',
-          module: 'https://cardstack.com/base/card-api',
+          module: '@cardstack/base/card-api',
           name: 'linksTo',
         },
         'the field type is correct',
@@ -971,7 +971,7 @@ module(basename(__filename), function () {
         fieldType: 'contains',
         fieldDefinitionType: 'field',
         fieldRef: {
-          module: rri('https://cardstack.com/base/string'),
+          module: rri('@cardstack/base/string'),
           name: 'default',
         },
         incomingRelativeTo: undefined,
@@ -1026,7 +1026,7 @@ module(basename(__filename), function () {
         },
         fieldName: 'age',
         fieldRef: {
-          module: rri('https://cardstack.com/base/number'),
+          module: rri('@cardstack/base/number'),
           name: 'default',
         },
         fieldType: 'contains',
@@ -1078,7 +1078,7 @@ module(basename(__filename), function () {
           },
           fieldName: 'firstName',
           fieldRef: {
-            module: rri('https://cardstack.com/base/string'),
+            module: rri('@cardstack/base/string'),
             name: 'default',
           },
           fieldType: 'contains',
@@ -1183,7 +1183,7 @@ module(basename(__filename), function () {
         },
         fieldName: 'artistNames',
         fieldRef: {
-          module: rri('https://cardstack.com/base/string'),
+          module: rri('@cardstack/base/string'),
           name: 'default',
         },
         fieldType: 'containsMany',
@@ -1243,7 +1243,7 @@ module(basename(__filename), function () {
         },
         fieldName: 'firstNameAdjusted',
         fieldRef: {
-          module: rri('https://cardstack.com/base/string'),
+          module: rri('@cardstack/base/string'),
           name: 'default',
         },
         fieldType: 'contains',
@@ -1303,7 +1303,7 @@ module(basename(__filename), function () {
         },
         fieldName: 'streetNameAdjusted',
         fieldRef: {
-          module: rri('https://cardstack.com/base/string'),
+          module: rri('@cardstack/base/string'),
           name: 'default',
         },
         fieldType: 'contains',
diff --git a/packages/realm-server/tests/prerendering-test.ts b/packages/realm-server/tests/prerendering-test.ts
index 1f1e6df9b24..05e834fd598 100644
--- a/packages/realm-server/tests/prerendering-test.ts
+++ b/packages/realm-server/tests/prerendering-test.ts
@@ -26,7 +26,7 @@ import {
   baseCardRef,
   trimExecutableExtension,
   rri,
-  baseRealm,
+  baseRealmRRI,
   baseRRI,
   executableExtensions,
 } from '@cardstack/runtime-common';
@@ -2414,7 +2414,7 @@ module(basename(__filename), function () {
           'search doc includes name',
         );
         assert.ok(
-          result.response.deps.includes(`${baseRealm.url}card-api`),
+          result.response.deps.includes(`${baseRealmRRI}card-api`),
           'deps include base card-api module (where FileDef is defined)',
         );
         assert.notOk(
@@ -2812,7 +2812,7 @@ module(basename(__filename), function () {
                     return {
                       filter: {
                         on: {
-                          module: rri('https://cardstack.com/base/card-api'),
+                          module: rri('@cardstack/base/card-api'),
                           name: 'FileDef',
                         },
                         eq: {
@@ -4060,7 +4060,7 @@ module(basename(__filename), function () {
                   },
                   meta: {
                     adoptsFrom: {
-                      module: rri('https://cardstack.com/base/brand-guide'),
+                      module: rri('@cardstack/base/brand-guide'),
                       name: 'default',
                     },
                   },
@@ -4329,9 +4329,7 @@ module(basename(__filename), function () {
         test('parent embedded HTML', function (assert) {
           assert.ok(
             /data-test-card-thumbnail-placeholder/.test(
-              result.embeddedHTML![
-                'https://cardstack.com/base/card-api/CardDef'
-              ],
+              result.embeddedHTML!['@cardstack/base/card-api/CardDef'],
             ),
             `failed to match embedded html:${JSON.stringify(result.embeddedHTML)}`,
           );
@@ -4417,7 +4415,7 @@ module(basename(__filename), function () {
         test('types', function (assert) {
           assert.deepEqual(result.types, [
             `${realmURL2}cat/Cat`,
-            'https://cardstack.com/base/card-api/CardDef',
+            '@cardstack/base/card-api/CardDef',
           ]);
         });
 
diff --git a/packages/realm-server/tests/publish-unpublish-realm-test.ts b/packages/realm-server/tests/publish-unpublish-realm-test.ts
index 4a058a1d233..0253d9c4134 100644
--- a/packages/realm-server/tests/publish-unpublish-realm-test.ts
+++ b/packages/realm-server/tests/publish-unpublish-realm-test.ts
@@ -540,7 +540,7 @@ module(basename(__filename), function () {
                 attributes: {},
                 meta: {
                   adoptsFrom: {
-                    module: 'https://cardstack.com/base/card-api',
+                    module: '@cardstack/base/card-api',
                     name: 'CardDef',
                   },
                 },
@@ -987,7 +987,7 @@ module(basename(__filename), function () {
             },
             meta: {
               adoptsFrom: {
-                module: 'https://cardstack.com/base/card-api',
+                module: '@cardstack/base/card-api',
                 name: 'CardDef',
               },
             },
@@ -1099,7 +1099,7 @@ module(basename(__filename), function () {
             attributes: { cardInfo: { name } },
             meta: {
               adoptsFrom: {
-                module: 'https://cardstack.com/base/card-api',
+                module: '@cardstack/base/card-api',
                 name: 'CardDef',
               },
             },
diff --git a/packages/realm-server/tests/realm-endpoints-test.ts b/packages/realm-server/tests/realm-endpoints-test.ts
index 47e208e3512..dc667e97d80 100644
--- a/packages/realm-server/tests/realm-endpoints-test.ts
+++ b/packages/realm-server/tests/realm-endpoints-test.ts
@@ -17,6 +17,7 @@ import { utimesSync } from 'fs';
 import type { Realm } from '@cardstack/runtime-common';
 import {
   baseRealm,
+  baseRealmRRI,
   baseRRI,
   CachingDefinitionLookup,
   SupportedMimeType,
@@ -292,7 +293,7 @@ module(basename(__filename), function () {
       let json = response.body;
       assert.strictEqual(json.data.type, 'file-meta');
       assert.deepEqual(json.data.meta?.adoptsFrom, {
-        module: `${baseRealm.url}markdown-file-def`,
+        module: `${baseRealmRRI}markdown-file-def`,
         name: 'MarkdownDef',
       });
 
@@ -2072,6 +2073,10 @@ module(basename(__filename), function () {
           testCreatePrerenderAuth,
         );
         virtualNetwork.addURLMapping(new URL(baseRealm.url), localBaseRealmURL);
+        virtualNetwork.addRealmMapping(
+          '@cardstack/base/',
+          localBaseRealmURL.href,
+        );
 
         ({ realm: base } = await createRealm({
           definitionLookup,
diff --git a/packages/realm-server/tests/realm-endpoints/dependencies-test.ts b/packages/realm-server/tests/realm-endpoints/dependencies-test.ts
index 5f2b199cf66..2188e5d7e67 100644
--- a/packages/realm-server/tests/realm-endpoints/dependencies-test.ts
+++ b/packages/realm-server/tests/realm-endpoints/dependencies-test.ts
@@ -67,9 +67,7 @@ module(`realm-endpoints/${basename(__filename)}`, function (hooks) {
     assert.strictEqual(entry.attributes.entryType, 'file');
     assert.false(entry.attributes.hasError);
     assert.true(
-      entry.attributes.dependencies.includes(
-        'https://cardstack.com/base/card-api',
-      ),
+      entry.attributes.dependencies.includes('@cardstack/base/card-api'),
       'includes consumed card-api module dependency',
     );
     assert.false(
diff --git a/packages/realm-server/tests/realm-endpoints/lint-test.ts b/packages/realm-server/tests/realm-endpoints/lint-test.ts
index 3a2129db87f..d1650792697 100644
--- a/packages/realm-server/tests/realm-endpoints/lint-test.ts
+++ b/packages/realm-server/tests/realm-endpoints/lint-test.ts
@@ -438,7 +438,7 @@ export class MyCard extends CardDef {
       let responseJson = JSON.parse(response.text);
       assert.strictEqual(
         responseJson.output,
-        `import StringField from 'https://cardstack.com/base/string';
+        `import StringField from '@cardstack/base/string';
 import { CardDef, field, contains } from 'https://cardstack.com/base/card-api';
 
 export class MyCard extends CardDef {
@@ -502,7 +502,7 @@ export class MyCard extends CardDef {
       assert.strictEqual(
         responseJson.output,
         `import { eq } from '@cardstack/boxel-ui/helpers';
-import StringField from 'https://cardstack.com/base/string';
+import StringField from '@cardstack/base/string';
 import { CardDef, field, contains } from 'https://cardstack.com/base/card-api';
 import MyComponent from 'somewhere';
 
@@ -681,7 +681,7 @@ export class MyCard extends CardDef {
 
       // Should use single quotes based on prettier configuration
       assert.ok(
-        responseJson.output.includes("'https://cardstack.com/base/string'"),
+        responseJson.output.includes("'@cardstack/base/string'"),
         'Single quotes are used for imports',
       );
       assert.ok(
@@ -714,7 +714,7 @@ export class MyCard extends CardDef {
       let responseJson = JSON.parse(response.text);
       assert.strictEqual(
         responseJson.output,
-        `import StringField from 'https://cardstack.com/base/string';
+        `import StringField from '@cardstack/base/string';
 import { CardDef, field, contains } from 'https://cardstack.com/base/card-api';
 export class MyCard extends CardDef {
   @field name = contains(StringField);
diff --git a/packages/realm-server/tests/realm-endpoints/search-test.ts b/packages/realm-server/tests/realm-endpoints/search-test.ts
index f4b9c198c0e..804f1563af7 100644
--- a/packages/realm-server/tests/realm-endpoints/search-test.ts
+++ b/packages/realm-server/tests/realm-endpoints/search-test.ts
@@ -1,7 +1,12 @@
 import { module, test } from 'qunit';
 import type { Test, SuperTest } from 'supertest';
 import { basename } from 'path';
-import { baseRealm, baseRRI, type Realm, rri } from '@cardstack/runtime-common';
+import {
+  baseRealmRRI,
+  baseRRI,
+  type Realm,
+  rri,
+} from '@cardstack/runtime-common';
 import type { Query } from '@cardstack/runtime-common/query';
 import {
   setupPermissionedRealmCached,
@@ -232,7 +237,7 @@ module(`realm-endpoints/${basename(__filename)}`, function () {
             .send({
               filter: {
                 on: {
-                  module: `${baseRealm.url}card-api`,
+                  module: `${baseRealmRRI}card-api`,
                   name: 'FileDef',
                 },
                 eq: {
@@ -264,7 +269,7 @@ module(`realm-endpoints/${basename(__filename)}`, function () {
             .send({
               filter: {
                 type: {
-                  module: `${baseRealm.url}markdown-file-def`,
+                  module: `${baseRealmRRI}markdown-file-def`,
                   name: 'MarkdownDef',
                 },
               },
diff --git a/packages/realm-server/tests/realm-file-changes-listener-test.ts b/packages/realm-server/tests/realm-file-changes-listener-test.ts
index b616f4941d0..12f7bb1f127 100644
--- a/packages/realm-server/tests/realm-file-changes-listener-test.ts
+++ b/packages/realm-server/tests/realm-file-changes-listener-test.ts
@@ -63,13 +63,10 @@ module(basename(__filename), function () {
     });
 
     test('parses url:path without a port in the url', function (assert) {
-      assert.deepEqual(
-        parsePayload('https://cardstack.com/base/:card-api.gts'),
-        {
-          url: 'https://cardstack.com/base/',
-          path: 'card-api.gts',
-        },
-      );
+      assert.deepEqual(parsePayload('@cardstack/base/:card-api.gts'), {
+        url: '@cardstack/base/',
+        path: 'card-api.gts',
+      });
     });
 
     test('parses a nested path', function (assert) {
diff --git a/packages/realm-server/tests/realm-identifiers-test.ts b/packages/realm-server/tests/realm-identifiers-test.ts
index 9a955526240..60580165ce5 100644
--- a/packages/realm-server/tests/realm-identifiers-test.ts
+++ b/packages/realm-server/tests/realm-identifiers-test.ts
@@ -119,7 +119,7 @@ module(basename(__filename), function () {
           relationships: {
             theme: {
               links: {
-                self: 'https://cardstack.com/base/Theme/brand-guide',
+                self: '@cardstack/base/Theme/brand-guide',
               },
             },
           },
@@ -140,7 +140,7 @@ module(basename(__filename), function () {
       assert.ok(rel, 'relationship exists after relativization');
       assert.strictEqual(
         rel.links.self,
-        'https://cardstack.com/base/Theme/brand-guide',
+        '@cardstack/base/Theme/brand-guide',
         'absolute URL to another realm is preserved as-is',
       );
     });
@@ -419,6 +419,33 @@ module(basename(__filename), function () {
           'http://other.example.com/foo',
         );
       });
+
+      test('chases through addURLMapping when the input is a virtual URL whose resolved form matches a registered prefix', function (assert) {
+        let vn = new VirtualNetwork();
+        vn.addURLMapping(
+          new URL('https://cardstack.com/base/'),
+          new URL('http://localhost:4201/base/'),
+        );
+        vn.addRealmMapping('@cardstack/base/', 'http://localhost:4201/base/');
+        assert.strictEqual(
+          vn.unresolveURL('https://cardstack.com/base/card-api'),
+          '@cardstack/base/card-api',
+          'virtual URL resolves through addURLMapping then matches @cardstack/base/',
+        );
+      });
+
+      test('returns the input unchanged when chase-through resolves but no realm prefix matches', function (assert) {
+        let vn = new VirtualNetwork();
+        vn.addURLMapping(
+          new URL('https://example.com/foo/'),
+          new URL('http://localhost:9999/foo/'),
+        );
+        assert.strictEqual(
+          vn.unresolveURL('https://example.com/foo/bar'),
+          'https://example.com/foo/bar',
+          'no realm-prefix mapping for the resolved URL — return input as-is',
+        );
+      });
     });
 
     module('toURL', function () {
diff --git a/packages/realm-server/tests/realm-registry-backfill-test.ts b/packages/realm-server/tests/realm-registry-backfill-test.ts
index a62322c24f1..153fa1c5f2b 100644
--- a/packages/realm-server/tests/realm-registry-backfill-test.ts
+++ b/packages/realm-server/tests/realm-registry-backfill-test.ts
@@ -56,7 +56,7 @@ function seedRealmJson(realmDir: string, payload: Record<string, unknown>) {
       },
       meta: {
         adoptsFrom: {
-          module: 'https://cardstack.com/base/realm-config',
+          module: '@cardstack/base/realm-config',
           name: 'RealmConfig',
         },
       },
@@ -92,16 +92,14 @@ module(basename(__filename), function () {
         dbAdapter,
         realmsRootPath,
         serverURL,
-        bootstrapRealms: [
-          { diskPath: bootstrapPath, url: 'https://cardstack.com/base/' },
-        ],
+        bootstrapRealms: [{ diskPath: bootstrapPath, url: '@cardstack/base/' }],
       });
 
       const rows = (await allRegistryRows(dbAdapter)).filter(
         (r) => r.kind === 'bootstrap',
       );
       assert.strictEqual(rows.length, 1, 'one bootstrap row written');
-      assert.strictEqual(rows[0].url, 'https://cardstack.com/base/');
+      assert.strictEqual(rows[0].url, '@cardstack/base/');
       assert.true(rows[0].pinned, 'pinned=true');
       assert.strictEqual(
         rows[0].owner_username,
@@ -190,9 +188,7 @@ module(basename(__filename), function () {
         dbAdapter,
         realmsRootPath,
         serverURL,
-        bootstrapRealms: [
-          { diskPath: bootstrapPath, url: 'https://cardstack.com/base/' },
-        ],
+        bootstrapRealms: [{ diskPath: bootstrapPath, url: '@cardstack/base/' }],
       };
       await runRegistryBackfill(opts);
       const firstRun = await allRegistryRows(dbAdapter);
@@ -218,9 +214,7 @@ module(basename(__filename), function () {
         dbAdapter,
         realmsRootPath,
         serverURL,
-        bootstrapRealms: [
-          { diskPath: pathA, url: 'https://cardstack.com/base/' },
-        ],
+        bootstrapRealms: [{ diskPath: pathA, url: '@cardstack/base/' }],
       });
       const firstDiskId = (await allRegistryRows(dbAdapter)).find(
         (r) => r.kind === 'bootstrap',
@@ -231,9 +225,7 @@ module(basename(__filename), function () {
         dbAdapter,
         realmsRootPath,
         serverURL,
-        bootstrapRealms: [
-          { diskPath: pathB, url: 'https://cardstack.com/base/' },
-        ],
+        bootstrapRealms: [{ diskPath: pathB, url: '@cardstack/base/' }],
       });
       const secondDiskId = (await allRegistryRows(dbAdapter)).find(
         (r) => r.kind === 'bootstrap',
diff --git a/packages/realm-server/tests/realm-registry-reconciler-test.ts b/packages/realm-server/tests/realm-registry-reconciler-test.ts
index 8df5348fb68..f71ce62fc81 100644
--- a/packages/realm-server/tests/realm-registry-reconciler-test.ts
+++ b/packages/realm-server/tests/realm-registry-reconciler-test.ts
@@ -87,7 +87,7 @@ module(basename(__filename), function () {
         owner_username: 'luke',
       });
       await seedRow(dbAdapter, {
-        url: 'https://cardstack.com/base/',
+        url: '@cardstack/base/',
         kind: 'bootstrap',
         disk_id: '/abs/base',
         owner_username: 'system',
@@ -102,17 +102,15 @@ module(basename(__filename), function () {
         'source',
       );
       assert.strictEqual(
-        reconciler.knownByUrl.get('https://cardstack.com/base/')?.kind,
+        reconciler.knownByUrl.get('@cardstack/base/')?.kind,
         'bootstrap',
       );
-      assert.true(
-        reconciler.knownByUrl.get('https://cardstack.com/base/')!.pinned,
-      );
+      assert.true(reconciler.knownByUrl.get('@cardstack/base/')!.pinned);
     });
 
     test('reconcile eagerly mounts pinned rows', async function (assert) {
       await seedRow(dbAdapter, {
-        url: 'https://cardstack.com/base/',
+        url: '@cardstack/base/',
         kind: 'bootstrap',
         disk_id: '/abs/base',
         owner_username: 'system',
@@ -121,9 +119,9 @@ module(basename(__filename), function () {
 
       await reconciler.reconcile();
 
-      assert.deepEqual(mountCalls, ['https://cardstack.com/base/']);
+      assert.deepEqual(mountCalls, ['@cardstack/base/']);
       assert.strictEqual(reconciler.mounted.size, 1);
-      assert.ok(reconciler.mounted.get('https://cardstack.com/base/'));
+      assert.ok(reconciler.mounted.get('@cardstack/base/'));
     });
 
     test('reconcile does NOT eagerly mount unpinned rows', async function (assert) {
@@ -155,7 +153,7 @@ module(basename(__filename), function () {
     });
 
     test('registerExistingMounts suppresses re-mount for pinned realms the legacy path already mounted', async function (assert) {
-      const url = 'https://cardstack.com/base/';
+      const url = '@cardstack/base/';
       await seedRow(dbAdapter, {
         url,
         kind: 'bootstrap',
@@ -372,7 +370,7 @@ module(basename(__filename), function () {
     });
 
     test('lookupOrMount returns mounted realm without re-mount', async function (assert) {
-      const url = 'https://cardstack.com/base/';
+      const url = '@cardstack/base/';
       await seedRow(dbAdapter, {
         url,
         kind: 'bootstrap',
diff --git a/packages/realm-server/tests/realm-registry-writes-test.ts b/packages/realm-server/tests/realm-registry-writes-test.ts
index d81473c6094..06bf24806c6 100644
--- a/packages/realm-server/tests/realm-registry-writes-test.ts
+++ b/packages/realm-server/tests/realm-registry-writes-test.ts
@@ -128,7 +128,7 @@ module(basename(__filename), function () {
     });
 
     test('does not clobber a bootstrap row that shares the URL', async function (assert) {
-      const url = 'https://cardstack.com/base/';
+      const url = '@cardstack/base/';
       await seedBootstrapRow(dbAdapter, url);
 
       await upsertPublishedRealmInRegistry(dbAdapter, {
@@ -236,7 +236,7 @@ module(basename(__filename), function () {
     });
 
     test('does NOT delete a bootstrap row (kind != bootstrap guard)', async function (assert) {
-      const url = 'https://cardstack.com/base/';
+      const url = '@cardstack/base/';
       await seedBootstrapRow(dbAdapter, url);
       await deleteRegistryRowByUrl(dbAdapter, url);
 
diff --git a/packages/realm-server/tests/realm-routing-test.ts b/packages/realm-server/tests/realm-routing-test.ts
index 293197312b4..1d8aa99be03 100644
--- a/packages/realm-server/tests/realm-routing-test.ts
+++ b/packages/realm-server/tests/realm-routing-test.ts
@@ -64,7 +64,7 @@ function makeRoutingFixture(): Record<
         },
         meta: {
           adoptsFrom: {
-            module: rri('https://cardstack.com/base/realm-config'),
+            module: rri('@cardstack/base/realm-config'),
             name: 'RealmConfig',
           },
         },
diff --git a/packages/realm-server/tests/search-prerendered-test.ts b/packages/realm-server/tests/search-prerendered-test.ts
index 360ccfaa4ba..6763be4c423 100644
--- a/packages/realm-server/tests/search-prerendered-test.ts
+++ b/packages/realm-server/tests/search-prerendered-test.ts
@@ -1241,11 +1241,11 @@ function assertScopedCssUrlsContain(
 
 // These modules have CSS that CardDef consumes, so we expect to see them in all relationships of a prerendered card
 let cardDefModuleDependencies = [
-  'https://cardstack.com/base/default-templates/embedded.gts',
-  'https://cardstack.com/base/default-templates/isolated-and-edit.gts',
-  'https://cardstack.com/base/default-templates/field-edit.gts',
-  'https://cardstack.com/base/field-component.gts',
-  'https://cardstack.com/base/contains-many-component.gts',
-  'https://cardstack.com/base/links-to-editor.gts',
-  'https://cardstack.com/base/links-to-many-component.gts',
+  '@cardstack/base/default-templates/embedded.gts',
+  '@cardstack/base/default-templates/isolated-and-edit.gts',
+  '@cardstack/base/default-templates/field-edit.gts',
+  '@cardstack/base/field-component.gts',
+  '@cardstack/base/contains-many-component.gts',
+  '@cardstack/base/links-to-editor.gts',
+  '@cardstack/base/links-to-many-component.gts',
 ];
diff --git a/packages/realm-server/tests/server-endpoints/download-realm-test.ts b/packages/realm-server/tests/server-endpoints/download-realm-test.ts
index f8519696cec..9f23aa26053 100644
--- a/packages/realm-server/tests/server-endpoints/download-realm-test.ts
+++ b/packages/realm-server/tests/server-endpoints/download-realm-test.ts
@@ -203,7 +203,7 @@ module(`server-endpoints/${basename(__filename)}`, function (hooks) {
             attributes: { cardInfo: { name: 'CS-11270 regression realm' } },
             meta: {
               adoptsFrom: {
-                module: 'https://cardstack.com/base/realm-config',
+                module: '@cardstack/base/realm-config',
                 name: 'RealmConfig',
               },
             },
diff --git a/packages/realm-server/tests/server-endpoints/federated-types-test.ts b/packages/realm-server/tests/server-endpoints/federated-types-test.ts
index e3a6956061d..2611c80916f 100644
--- a/packages/realm-server/tests/server-endpoints/federated-types-test.ts
+++ b/packages/realm-server/tests/server-endpoints/federated-types-test.ts
@@ -53,7 +53,7 @@ module(`server-endpoints/${basename(__filename)}`, function (_hooks) {
           },
           meta: {
             adoptsFrom: {
-              module: rri('https://cardstack.com/base/card-api'),
+              module: rri('@cardstack/base/card-api'),
               name: 'CardDef',
             },
           },
diff --git a/packages/realm-server/tests/server-endpoints/index-responses-test.ts b/packages/realm-server/tests/server-endpoints/index-responses-test.ts
index ef5c74cd44d..82e3234c1b5 100644
--- a/packages/realm-server/tests/server-endpoints/index-responses-test.ts
+++ b/packages/realm-server/tests/server-endpoints/index-responses-test.ts
@@ -351,7 +351,7 @@ module(`server-endpoints/${basename(__filename)}`, function () {
               },
               meta: {
                 adoptsFrom: {
-                  module: rri('https://cardstack.com/base/card-api'),
+                  module: rri('@cardstack/base/card-api'),
                   name: 'Theme',
                 },
               },
@@ -368,7 +368,7 @@ module(`server-endpoints/${basename(__filename)}`, function () {
               },
               meta: {
                 adoptsFrom: {
-                  module: rri('https://cardstack.com/base/brand-guide'),
+                  module: rri('@cardstack/base/brand-guide'),
                   name: 'default',
                 },
               },
@@ -1442,7 +1442,7 @@ module(`server-endpoints/${basename(__filename)}`, function () {
                   },
                   meta: {
                     adoptsFrom: {
-                      module: 'https://cardstack.com/base/brand-guide',
+                      module: '@cardstack/base/brand-guide',
                       name: 'default',
                     },
                   },
@@ -1474,7 +1474,7 @@ module(`server-endpoints/${basename(__filename)}`, function () {
                   },
                   meta: {
                     adoptsFrom: {
-                      module: 'https://cardstack.com/base/card-api',
+                      module: '@cardstack/base/card-api',
                       name: 'CardDef',
                     },
                   },
diff --git a/packages/realm-server/tests/server-endpoints/realm-lifecycle-test.ts b/packages/realm-server/tests/server-endpoints/realm-lifecycle-test.ts
index 21c901a3fa6..868841b12ee 100644
--- a/packages/realm-server/tests/server-endpoints/realm-lifecycle-test.ts
+++ b/packages/realm-server/tests/server-endpoints/realm-lifecycle-test.ts
@@ -117,7 +117,7 @@ module(`server-endpoints/${basename(__filename)}`, function () {
               },
               meta: {
                 adoptsFrom: {
-                  module: 'https://cardstack.com/base/realm-config',
+                  module: '@cardstack/base/realm-config',
                   name: 'RealmConfig',
                 },
               },
@@ -166,7 +166,7 @@ module(`server-endpoints/${basename(__filename)}`, function () {
                 attributes: { cardInfo: { name: 'Test Card' } },
                 meta: {
                   adoptsFrom: {
-                    module: 'https://cardstack.com/base/card-api',
+                    module: '@cardstack/base/card-api',
                     name: 'CardDef',
                   },
                 },
@@ -308,7 +308,7 @@ module(`server-endpoints/${basename(__filename)}`, function () {
                 },
                 meta: {
                   adoptsFrom: {
-                    module: 'https://cardstack.com/base/card-api',
+                    module: '@cardstack/base/card-api',
                     name: 'CardDef',
                   },
                 },
@@ -373,7 +373,7 @@ module(`server-endpoints/${basename(__filename)}`, function () {
                 attributes: { cardInfo: { name: 'Test Card' } },
                 meta: {
                   adoptsFrom: {
-                    module: 'https://cardstack.com/base/card-api',
+                    module: '@cardstack/base/card-api',
                     name: 'CardDef',
                   },
                 },
diff --git a/packages/realm-server/tests/server-endpoints/run-command-endpoint-test.ts b/packages/realm-server/tests/server-endpoints/run-command-endpoint-test.ts
index 244abb06f5c..47677bbc00f 100644
--- a/packages/realm-server/tests/server-endpoints/run-command-endpoint-test.ts
+++ b/packages/realm-server/tests/server-endpoints/run-command-endpoint-test.ts
@@ -110,7 +110,7 @@ module(`server-endpoints/${basename(__filename)}`, function () {
                 '@cardstack/boxel-host/commands/get-card-type-schema/default',
               commandInput: {
                 codeRef: {
-                  module: 'https://cardstack.com/base/card-api',
+                  module: '@cardstack/base/card-api',
                   name: 'CardDef',
                 },
               },
diff --git a/packages/realm-server/tests/server-endpoints/search-prerendered-test.ts b/packages/realm-server/tests/server-endpoints/search-prerendered-test.ts
index 75e94f9ed72..625a97a51b9 100644
--- a/packages/realm-server/tests/server-endpoints/search-prerendered-test.ts
+++ b/packages/realm-server/tests/server-endpoints/search-prerendered-test.ts
@@ -51,7 +51,7 @@ module(`server-endpoints/${basename(__filename)}`, function (_hooks) {
             },
             meta: {
               adoptsFrom: {
-                module: rri('https://cardstack.com/base/card-api'),
+                module: rri('@cardstack/base/card-api'),
                 name: 'CardDef',
               },
             },
@@ -67,7 +67,7 @@ module(`server-endpoints/${basename(__filename)}`, function (_hooks) {
             },
             meta: {
               adoptsFrom: {
-                module: rri('https://cardstack.com/base/card-api'),
+                module: rri('@cardstack/base/card-api'),
                 name: 'CardDef',
               },
             },
diff --git a/packages/realm-server/tests/server-endpoints/search-test.ts b/packages/realm-server/tests/server-endpoints/search-test.ts
index 8ea600b5d4e..5996daf865b 100644
--- a/packages/realm-server/tests/server-endpoints/search-test.ts
+++ b/packages/realm-server/tests/server-endpoints/search-test.ts
@@ -57,7 +57,7 @@ module(`server-endpoints/${basename(__filename)}`, function (_hooks) {
           },
           meta: {
             adoptsFrom: {
-              module: rri('https://cardstack.com/base/card-api'),
+              module: rri('@cardstack/base/card-api'),
               name: 'CardDef',
             },
           },
@@ -73,7 +73,7 @@ module(`server-endpoints/${basename(__filename)}`, function (_hooks) {
           },
           meta: {
             adoptsFrom: {
-              module: rri('https://cardstack.com/base/card-api'),
+              module: rri('@cardstack/base/card-api'),
               name: 'CardDef',
             },
           },
diff --git a/packages/realm-server/tests/types-endpoint-test.ts b/packages/realm-server/tests/types-endpoint-test.ts
index 014777b2fa0..fe88b07f625 100644
--- a/packages/realm-server/tests/types-endpoint-test.ts
+++ b/packages/realm-server/tests/types-endpoint-test.ts
@@ -215,7 +215,7 @@ module(basename(__filename), function () {
         },
         {
           type: 'card-type-summary',
-          id: 'https://cardstack.com/base/realm-config/RealmConfig',
+          id: '@cardstack/base/realm-config/RealmConfig',
           attributes: {
             displayName: 'Realm Config',
             total: 1,
diff --git a/packages/realm-server/worker.ts b/packages/realm-server/worker.ts
index 4741207b83e..917cdb69d6a 100644
--- a/packages/realm-server/worker.ts
+++ b/packages/realm-server/worker.ts
@@ -133,6 +133,13 @@ for (let i = 0; i < fromUrls.length; i++) {
   let to = new URL(String(toUrls[i]));
   if (isUrlLike(from)) {
     virtualNetwork.addURLMapping(new URL(from), to);
+    // Convention: https://cardstack.com/X/ aliases @cardstack/X/. Also
+    // register the realm-prefix mapping so unresolveURL on either form
+    // produces the same canonical RRI — same reasoning as main.ts.
+    let m = from.match(/^https:\/\/cardstack\.com\/([^/]+)\/$/);
+    if (m) {
+      virtualNetwork.addRealmMapping(`@cardstack/${m[1]}/`, to.href);
+    }
   } else {
     virtualNetwork.addRealmMapping(from, to.href);
   }
diff --git a/packages/runtime-common/constants.ts b/packages/runtime-common/constants.ts
index 2927bde6eba..b62124f6d21 100644
--- a/packages/runtime-common/constants.ts
+++ b/packages/runtime-common/constants.ts
@@ -1,43 +1,58 @@
 import { RealmPaths } from './paths.ts';
 import type { ResolvedCodeRef } from './code-ref.ts';
-import { rri, type RealmResourceIdentifier } from './realm-identifiers.ts';
+import {
+  ri,
+  rri,
+  type RealmIdentifier,
+  type RealmResourceIdentifier,
+} from './realm-identifiers.ts';
 import type { RealmPermissions } from './index.ts';
 
 export const baseRealm = new RealmPaths(new URL('https://cardstack.com/base/'));
 
+/**
+ * The base realm's canonical RRI prefix. Use this when building code
+ * refs that should match what `Loader.identify` / `identifyCard` emit
+ * for base-realm classes (which canonicalise via `vn.unresolveURL`
+ * to the registered `@cardstack/base/` prefix).
+ */
+export const baseRealmRRI: RealmIdentifier = ri('@cardstack/base/');
+
 /**
  * Build a `RealmResourceIdentifier` for a module inside the base realm.
- * Equivalent to `` rri(`${baseRealm.url}${path}`) `` but shorter.
+ * Returns the prefix-form RRI (e.g. `@cardstack/base/card-api`) so the
+ * value matches what `Loader.identify` / `identifyCard` emit for
+ * base-realm classes after the runtime's `unresolveURL` chase.
  */
 export function baseRRI(path: string): RealmResourceIdentifier {
-  return rri(`${baseRealm.url}${path}`);
+  return rri(`${baseRealmRRI}${path}`);
 }
 
 export const devSkillLocalPath = 'Skill/boxel-development';
 export const envSkillLocalPath = 'Skill/boxel-environment';
 
 export const baseRef: ResolvedCodeRef = {
-  module: `${baseRealm.url}card-api` as RealmResourceIdentifier,
+  module: `${baseRealmRRI}card-api` as RealmResourceIdentifier,
   name: 'BaseDef',
 };
 export const specRef: ResolvedCodeRef = {
-  module: `${baseRealm.url}spec` as RealmResourceIdentifier,
+  module: `${baseRealmRRI}spec` as RealmResourceIdentifier,
   name: 'Spec',
 };
 export const baseCardRef: ResolvedCodeRef = {
-  module: `${baseRealm.url}card-api` as RealmResourceIdentifier,
+  module: `${baseRealmRRI}card-api` as RealmResourceIdentifier,
   name: 'CardDef',
 };
 export const baseFieldRef: ResolvedCodeRef = {
-  module: `${baseRealm.url}card-api` as RealmResourceIdentifier,
+  module: `${baseRealmRRI}card-api` as RealmResourceIdentifier,
   name: 'FieldDef',
 };
 export const skillCardRef: ResolvedCodeRef = {
-  module: `${baseRealm.url}skill` as RealmResourceIdentifier,
+  module: `${baseRealmRRI}skill` as RealmResourceIdentifier,
   name: 'Skill',
 };
 export const baseFileRef: ResolvedCodeRef = {
-  module: `${baseRealm.url}card-api` as RealmResourceIdentifier,
+  module: `${baseRealmRRI}card-api` as RealmResourceIdentifier,
   name: 'FileDef',
 };
 
diff --git a/packages/runtime-common/definition-lookup.ts b/packages/runtime-common/definition-lookup.ts
index 367e4f4a164..61af1ab6e52 100644
--- a/packages/runtime-common/definition-lookup.ts
+++ b/packages/runtime-common/definition-lookup.ts
@@ -106,7 +106,7 @@ function canonicalURL(
   // to real URLs so that realm-membership checks and DB lookups work.
   if (virtualNetwork.isRegisteredPrefix(url)) {
     try {
-      return virtualNetwork.toURL(url).href;
+      return toFetchableForm(virtualNetwork.toURL(url), virtualNetwork);
     } catch (_e) {
       // fall through to normal URL handling
     }
@@ -115,13 +115,28 @@ function canonicalURL(
     let parsed = new URL(url, relativeTo);
     parsed.search = '';
     parsed.hash = '';
-    return parsed.href;
+    return toFetchableForm(parsed, virtualNetwork);
   } catch (_e) {
     let stripped = url.split('#')[0] ?? url;
     return stripped.split('?')[0] ?? stripped;
   }
 }
 
+// A base-realm module resolves to a real URL (e.g.
+// `http://localhost:4201/base/X`), but that realm is reachable in-process
+// only under its virtual-alias URL (`https://cardstack.com/base/X`) — the
+// alias is what the loader's mounted handler / origin-matched auth
+// interceptor recognizes. A direct fetch of the bare real URL bypasses
+// that and fails at the transport, poisoning the module's definition
+// entry. When a real→virtual URL mapping is registered (only base today),
+// return the alias form so the definition-load target is fetchable.
+// Realms with no alias map (user realms, catalog, …) are served at their
+// real URL and are returned unchanged.
+function toFetchableForm(real: URL, virtualNetwork: VirtualNetwork): string {
+  let virtual = virtualNetwork.mapURL(real, 'real-to-virtual');
+  return (virtual ?? real).href;
+}
+
 function normalizeExecutableURL(url: string): string {
   return trimExecutableExtension(rri(url));
 }
@@ -1155,8 +1170,29 @@ export class CachingDefinitionLookup implements DefinitionLookup {
     cacheUserId: string;
     prerenderUserId: string;
   } | null> {
+    // `canonicalURL` of an RRI-prefix input resolves to the realm's
+    // RESOLVED real URL via `vn.toURL` (e.g. `@cardstack/base/foo` →
+    // `https://localhost:4201/base/foo`), while `#realms` is keyed by
+    // the user-facing realm URL — typically the virtual alias like
+    // `https://cardstack.com/base/`. The direct startsWith check
+    // therefore misses local realms whenever the input was RRI form
+    // (or whenever realm.url is the virtual alias and the input
+    // canonicalised to the resolved URL).
+    //
+    // Normalize both sides to RRI form via `unresolveURL` (which
+    // chases through any registered virtual → real URL mapping and
+    // matches against realm-prefix targets) so the comparison is
+    // form-agnostic. After normalization, `https://localhost:4201/base/foo`,
+    // `https://cardstack.com/base/foo`, and `@cardstack/base/foo` all
+    // become `@cardstack/base/foo`.
+    let vn = this.#virtualNetwork;
+    let normalizedModuleURL = vn.unresolveURL(moduleURL);
     let localRealm = this.#realms.find((realm) => {
-      return moduleURL.startsWith(realm.url);
+      if (moduleURL.startsWith(realm.url)) {
+        return true;
+      }
+      let normalizedRealmURL = vn.unresolveURL(realm.url);
+      return normalizedModuleURL.startsWith(normalizedRealmURL);
     });
 
     if (localRealm) {
diff --git a/packages/runtime-common/etc/eslint/missing-card-api-import-config.js b/packages/runtime-common/etc/eslint/missing-card-api-import-config.js
index 60d2cc942cf..13f99c5ced7 100644
--- a/packages/runtime-common/etc/eslint/missing-card-api-import-config.js
+++ b/packages/runtime-common/etc/eslint/missing-card-api-import-config.js
@@ -4,46 +4,43 @@
 module.exports = {
   importMappings: {
     // card-api methods, classes and decorators
-    Component: ['Component', 'https://cardstack.com/base/card-api'],
-    CardDef: ['CardDef', 'https://cardstack.com/base/card-api'],
-    FieldDef: ['FieldDef', 'https://cardstack.com/base/card-api'],
-    field: ['field', 'https://cardstack.com/base/card-api'],
-    contains: ['contains', 'https://cardstack.com/base/card-api'],
-    linksTo: ['linksTo', 'https://cardstack.com/base/card-api'],
-    containsMany: ['containsMany', 'https://cardstack.com/base/card-api'],
-    linksToMany: ['linksToMany', 'https://cardstack.com/base/card-api'],
+    Component: ['Component', '@cardstack/base/card-api'],
+    CardDef: ['CardDef', '@cardstack/base/card-api'],
+    FieldDef: ['FieldDef', '@cardstack/base/card-api'],
+    field: ['field', '@cardstack/base/card-api'],
+    contains: ['contains', '@cardstack/base/card-api'],
+    linksTo: ['linksTo', '@cardstack/base/card-api'],
+    containsMany: ['containsMany', '@cardstack/base/card-api'],
+    linksToMany: ['linksToMany', '@cardstack/base/card-api'],
 
     // Base realm field defs
-    AddressField: ['default', 'https://cardstack.com/base/address'],
-    Base64ImageField: ['default', 'https://cardstack.com/base/base64-image'],
-    BigIntegerField: ['default', 'https://cardstack.com/base/big-integer'],
-    BooleanField: ['default', 'https://cardstack.com/base/boolean'],
-    CodeRefField: ['default', 'https://cardstack.com/base/code-ref'],
-    ColorField: ['default', 'https://cardstack.com/base/color'],
-    CoordinateField: ['default', 'https://cardstack.com/base/coordinate'],
-    CountryField: ['default', 'https://cardstack.com/base/country'],
-    DateField: ['default', 'https://cardstack.com/base/date'],
-    DateRangeField: ['default', 'https://cardstack.com/base/date-range-field'],
-    DateTimeField: ['default', 'https://cardstack.com/base/datetime'],
-    EmailField: ['default', 'https://cardstack.com/base/email'],
-    EthereumAddressField: [
-      'default',
-      'https://cardstack.com/base/ethereum-address',
-    ],
-    MarkdownField: ['default', 'https://cardstack.com/base/markdown'],
-    NumberField: ['default', 'https://cardstack.com/base/number'],
-    PercentageField: ['default', 'https://cardstack.com/base/percentage'],
-    PhoneNumberField: ['default', 'https://cardstack.com/base/phone-number'],
-    StringField: ['default', 'https://cardstack.com/base/string'],
-    TextAreaField: ['default', 'https://cardstack.com/base/text-area'],
-    URLField: ['default', 'https://cardstack.com/base/url'],
-    WebsiteField: ['default', 'https://cardstack.com/base/website'],
+    AddressField: ['default', '@cardstack/base/address'],
+    Base64ImageField: ['default', '@cardstack/base/base64-image'],
+    BigIntegerField: ['default', '@cardstack/base/big-integer'],
+    BooleanField: ['default', '@cardstack/base/boolean'],
+    CodeRefField: ['default', '@cardstack/base/code-ref'],
+    ColorField: ['default', '@cardstack/base/color'],
+    CoordinateField: ['default', '@cardstack/base/coordinate'],
+    CountryField: ['default', '@cardstack/base/country'],
+    DateField: ['default', '@cardstack/base/date'],
+    DateRangeField: ['default', '@cardstack/base/date-range-field'],
+    DateTimeField: ['default', '@cardstack/base/datetime'],
+    EmailField: ['default', '@cardstack/base/email'],
+    EthereumAddressField: ['default', '@cardstack/base/ethereum-address'],
+    MarkdownField: ['default', '@cardstack/base/markdown'],
+    NumberField: ['default', '@cardstack/base/number'],
+    PercentageField: ['default', '@cardstack/base/percentage'],
+    PhoneNumberField: ['default', '@cardstack/base/phone-number'],
+    StringField: ['default', '@cardstack/base/string'],
+    TextAreaField: ['default', '@cardstack/base/text-area'],
+    URLField: ['default', '@cardstack/base/url'],
+    WebsiteField: ['default', '@cardstack/base/website'],
 
     // Enumerations
-    enumField: ['default', 'https://cardstack.com/base/enum'],
-    enumConfig: ['enumConfig', 'https://cardstack.com/base/enum'],
+    enumField: ['default', '@cardstack/base/enum'],
+    enumConfig: ['enumConfig', '@cardstack/base/enum'],
 
     // More
-    Skill: ['default', 'https://cardstack.com/base/skill'],
+    Skill: ['default', '@cardstack/base/skill'],
   },
 };
diff --git a/packages/runtime-common/index-query-engine.ts b/packages/runtime-common/index-query-engine.ts
index ff5bb4a7ed7..b79b10bfbc1 100644
--- a/packages/runtime-common/index-query-engine.ts
+++ b/packages/runtime-common/index-query-engine.ts
@@ -9,7 +9,7 @@ import {
   baseCardRef,
   internalKeyFor,
   isResolvedCodeRef,
-  baseRealm,
+  baseRealmRRI,
   getSerializer,
 } from './index.ts';
 import {
@@ -1828,7 +1828,7 @@ async function getField(
         isPrimitive: true,
         isComputed: false,
         fieldOrCard: {
-          module: `${baseRealm.url}card-api`,
+          module: `${baseRealmRRI}card-api`,
           name: 'StringField',
         },
       } as FieldDefinition;
diff --git a/packages/runtime-common/index.ts b/packages/runtime-common/index.ts
index 1cd39ca35f8..b3b51ec16b8 100644
--- a/packages/runtime-common/index.ts
+++ b/packages/runtime-common/index.ts
@@ -1241,9 +1241,7 @@ export async function apiFor(
   let loader =
     Loader.getLoaderFor(cardOrFieldOrClass) ??
     loaderFor(cardOrFieldOrClass as CardDef | FieldDef | BaseDef);
-  let api = await loader.import<typeof CardAPI>(
-    'https://cardstack.com/base/card-api',
-  );
+  let api = await loader.import<typeof CardAPI>('@cardstack/base/card-api');
   if (!api) {
     throw new Error(`could not load card API`);
   }
diff --git a/packages/runtime-common/loader.ts b/packages/runtime-common/loader.ts
index 8282d0b23b3..527cf9da0ed 100644
--- a/packages/runtime-common/loader.ts
+++ b/packages/runtime-common/loader.ts
@@ -391,10 +391,17 @@ export class Loader {
     let resolvedModule = new URL(moduleIdentifier);
     let resolvedModuleIdentifier = resolvedModule.href;
     if (!this.moduleShims.has(resolvedModuleIdentifier)) {
-      trackRuntimeModuleDependency(
-        resolvedModuleIdentifier,
-        dependencyTrackingContext,
-      );
+      // Normalize tracker keys to the virtual-alias URL form when one
+      // exists (the dependency tracker requires `http://`/`https://`
+      // URLs — see `canonicalURL` in dependency-tracker.ts — so RRI
+      // prefix forms can't be used as keys). Without this, a base
+      // module imported via the virtual alias
+      // (`https://cardstack.com/base/X`) and the same module imported
+      // via the RRI prefix (`@cardstack/base/X` → resolveImport →
+      // resolved real URL `https://localhost:4201/base/X`) get tracked
+      // as two separate entries.
+      let trackingKey = this.canonicalizeTrackingKey(resolvedModuleIdentifier);
+      trackRuntimeModuleDependency(trackingKey, dependencyTrackingContext);
     }
 
     await this.advanceToState(resolvedModule, 'evaluated');
@@ -462,10 +469,11 @@ export class Loader {
       rootModuleIdentifier,
     )) {
       if (!this.moduleShims.has(moduleIdentifier)) {
-        trackRuntimeModuleDependency(
-          moduleIdentifier,
-          dependencyTrackingContext,
-        );
+        // Same canonicalization as the top-level import-time tracking
+        // call — collapse virtual-alias / resolved real URL forms onto
+        // the virtual-alias URL.
+        let trackingKey = this.canonicalizeTrackingKey(moduleIdentifier);
+        trackRuntimeModuleDependency(trackingKey, dependencyTrackingContext);
       }
     }
   }
@@ -788,6 +796,24 @@ export class Loader {
     return this.moduleCanonicalURLs.get(trimModuleIdentifier(moduleIdentifier));
   }
 
+  // Collapse a module identifier to its virtual-alias URL form when one
+  // exists, so the dependency tracker keys aren't fragmented across the
+  // virtual-alias (`https://cardstack.com/base/X`) and resolved real URL
+  // (`https://localhost:4201/base/X`) for the same module. Returns the
+  // input unchanged when no virtual alias is registered.
+  private canonicalizeTrackingKey(moduleIdentifier: string): string {
+    if (!this.virtualNetwork) {
+      return moduleIdentifier;
+    }
+    try {
+      let parsed = new URL(moduleIdentifier);
+      let virtual = this.virtualNetwork.mapURL(parsed, 'real-to-virtual');
+      return virtual ? virtual.href : moduleIdentifier;
+    } catch {
+      return moduleIdentifier;
+    }
+  }
+
   private captureIdentitiesOfModuleExports(
     module: any,
     moduleIdentifier: string,
diff --git a/packages/runtime-common/module-syntax.ts b/packages/runtime-common/module-syntax.ts
index 42d6f273d95..5366b3b084c 100644
--- a/packages/runtime-common/module-syntax.ts
+++ b/packages/runtime-common/module-syntax.ts
@@ -450,15 +450,41 @@ function makeNewField({
     return `@${fieldDecorator.name} ${fieldName} = ${fieldTypeIdentifier.name}(() => ${fieldRef.name});`;
   }
 
+  // Canonicalize `fieldRef.module` to the registered RRI prefix form
+  // (e.g. `@cardstack/base/X`) so generated import lines use the stable
+  // identifier rather than a deployment-specific real URL.
+  let canonicalFieldModule = virtualNetwork.unresolveURL(fieldRef.module);
+
   let relativeFieldModuleRef;
   if (incomingRelativeTo && outgoingRelativeTo) {
+    let resolved = virtualNetwork.resolveURL(
+      canonicalFieldModule,
+      incomingRelativeTo,
+    );
+    let canonical = virtualNetwork.unresolveURL(resolved.href);
     relativeFieldModuleRef = maybeRelativeReference(
-      virtualNetwork.resolveURL(fieldRef.module, incomingRelativeTo),
+      canonical,
       outgoingRelativeTo,
       outgoingRealmURL,
     );
   } else {
-    relativeFieldModuleRef = fieldRef.module;
+    relativeFieldModuleRef = canonicalFieldModule;
+  }
+
+  // `ImportUtil` matches existing imports by exact source string. The
+  // file may still use the virtual-alias URL form
+  // (`https://cardstack.com/base/X`) for an equivalent module while the
+  // canonical form is the RRI prefix (`@cardstack/base/X`). Reuse the
+  // existing import specifier when one matches under VN canonicalization
+  // so we merge instead of emitting a duplicate import line.
+  let existingEquivalentSource = findEquivalentImportSource(
+    programPath,
+    relativeFieldModuleRef,
+    incomingRelativeTo,
+    virtualNetwork,
+  );
+  if (existingEquivalentSource) {
+    relativeFieldModuleRef = existingEquivalentSource;
   }
 
   let fieldCardIdentifier = importUtil.import(
@@ -489,6 +515,51 @@ function makeNewField({
   return `@${fieldDecorator.name} ${fieldName} = ${fieldTypeIdentifier.name}(${fieldCardIdentifier.name});`;
 }
 
+// Returns the source string of an existing `ImportDeclaration` that
+// resolves to the same module as `targetSpecifier` under VN
+// canonicalization (RRI prefix vs. registered URL alias), so callers
+// can merge new identifiers into the existing import line rather than
+// emitting a duplicate. Returns undefined when no existing import
+// matches or when the file is being authored against the canonical
+// specifier directly.
+function findEquivalentImportSource(
+  programPath: NodePath<t.Program>,
+  targetSpecifier: string,
+  relativeTo: RealmResourceIdentifier | URL | undefined,
+  virtualNetwork: VirtualNetwork,
+): string | undefined {
+  let targetCanonical: string;
+  try {
+    targetCanonical = virtualNetwork.unresolveURL(
+      virtualNetwork.resolveURL(targetSpecifier, relativeTo).href,
+    );
+  } catch {
+    return undefined;
+  }
+  for (let node of programPath.node.body) {
+    if (node.type !== 'ImportDeclaration') {
+      continue;
+    }
+    let source = node.source.value;
+    if (source === targetSpecifier) {
+      // already exact-match — importUtil will merge without help
+      return undefined;
+    }
+    let sourceCanonical: string;
+    try {
+      sourceCanonical = virtualNetwork.unresolveURL(
+        virtualNetwork.resolveURL(source, relativeTo).href,
+      );
+    } catch {
+      continue;
+    }
+    if (sourceCanonical === targetCanonical) {
+      return source;
+    }
+  }
+  return undefined;
+}
+
 function getProgramPath(path: NodePath<any>): NodePath<t.Program> {
   let currentPath: NodePath | null = path;
   while (currentPath && currentPath.type !== 'Program') {
diff --git a/packages/runtime-common/realm-index-query-engine.ts b/packages/runtime-common/realm-index-query-engine.ts
index 8db24b8e5be..0239fd2e65d 100644
--- a/packages/runtime-common/realm-index-query-engine.ts
+++ b/packages/runtime-common/realm-index-query-engine.ts
@@ -3,7 +3,7 @@ import cloneDeep from 'lodash/cloneDeep';
 import {
   SupportedMimeType,
   isJsonContentType,
-  baseRealm,
+  baseRealmRRI,
   inferContentType,
   unixTime,
   maxLinkDepth,
@@ -2492,7 +2492,7 @@ function fileResourceFromIndex(
     (isCodeRef(fileEntry.resource?.meta?.adoptsFrom)
       ? fileEntry.resource?.meta?.adoptsFrom
       : {
-          module: `${baseRealm.url}card-api`,
+          module: `${baseRealmRRI}card-api`,
           name: 'FileDef',
         });
   let resourceAttributes = fileEntry.resource?.attributes ?? {};
diff --git a/packages/runtime-common/realm.ts b/packages/runtime-common/realm.ts
index 6f9f321ec5f..26a3859f4e0 100644
--- a/packages/runtime-common/realm.ts
+++ b/packages/runtime-common/realm.ts
@@ -3008,7 +3008,11 @@ export class Realm {
     if (!maybeFileRef) {
       return {
         kind: 'not-found',
-        response: notFound(request, requestContext, `${request.url} not found`),
+        response: notFound(
+          request,
+          requestContext,
+          `${this.#virtualNetwork.unresolveURL(request.url)} not found`,
+        ),
       };
     }
 
@@ -6887,7 +6891,7 @@ export class Realm {
           attributes: {},
           meta: {
             adoptsFrom: {
-              module: 'https://cardstack.com/base/realm-config',
+              module: '@cardstack/base/realm-config',
               name: 'RealmConfig',
             },
           },
@@ -6921,7 +6925,8 @@ export class Realm {
         let adoptsFrom = (cardDoc!.data as any).meta?.adoptsFrom;
         if (
           !isPlainObject(adoptsFrom) ||
-          adoptsFrom.module !== 'https://cardstack.com/base/realm-config' ||
+          this.#virtualNetwork.unresolveURL(adoptsFrom.module) !==
+            '@cardstack/base/realm-config' ||
           adoptsFrom.name !== 'RealmConfig'
         ) {
           return systemError({
diff --git a/packages/runtime-common/schema-analysis-plugin.ts b/packages/runtime-common/schema-analysis-plugin.ts
index 83ddd8fbd84..bfc0c5b7bea 100644
--- a/packages/runtime-common/schema-analysis-plugin.ts
+++ b/packages/runtime-common/schema-analysis-plugin.ts
@@ -193,7 +193,8 @@ const coreVisitor = {
     let isCardApiFile =
       path.node.loc &&
       'filename' in path.node.loc &&
-      path.node.loc.filename === 'https://cardstack.com/base/card-api';
+      (path.node.loc.filename === '@cardstack/base/card-api' ||
+        path.node.loc.filename === 'https://cardstack.com/base/card-api');
     let decoratorInfo = getNamedImportInfo(path.scope, expression.node.name);
     if (!decoratorInfo && !isCardApiFile) {
       return; // our @field decorator must originate from a named import
diff --git a/packages/runtime-common/tests/normalize-realm-meta-value-test.ts b/packages/runtime-common/tests/normalize-realm-meta-value-test.ts
index 68b26c5aab4..32742734c41 100644
--- a/packages/runtime-common/tests/normalize-realm-meta-value-test.ts
+++ b/packages/runtime-common/tests/normalize-realm-meta-value-test.ts
@@ -12,7 +12,7 @@ const personSummary: CardTypeSummary = {
 };
 
 const markdownSummary: CardTypeSummary = {
-  code_ref: 'https://cardstack.com/base/markdown-file-def/MarkdownDef',
+  code_ref: '@cardstack/base/markdown-file-def/MarkdownDef',
   display_name: 'Markdown',
   total: 5,
   icon_html: '<svg />',
diff --git a/packages/runtime-common/tests/package-shim-handler-test.ts b/packages/runtime-common/tests/package-shim-handler-test.ts
index d44da53af0c..42e77b5fdf8 100644
--- a/packages/runtime-common/tests/package-shim-handler-test.ts
+++ b/packages/runtime-common/tests/package-shim-handler-test.ts
@@ -222,7 +222,7 @@ const tests: SharedTests<Record<string, never>> = Object.freeze({
       );
       handler.shimModule('@cardstack/runtime-common', {
         Loader: class {},
-        baseRealm: 'https://cardstack.com/base/',
+        baseRealm: '@cardstack/base/',
       });
       let requestUrl = `${PACKAGES_FAKE_ORIGIN}@cardstack/runtime-common`;
       let response = await handler.handle(new Request(requestUrl));
@@ -259,7 +259,7 @@ const tests: SharedTests<Record<string, never>> = Object.freeze({
       // `/marked-sync` subpath, not on the main runtime-common barrel.
       handler.shimModule('@cardstack/runtime-common', {
         Loader: class {},
-        baseRealm: 'https://cardstack.com/base/',
+        baseRealm: '@cardstack/base/',
       });
       handler.shimModule('@cardstack/runtime-common/marked-sync', {
         markdownToHtml: () => '',
diff --git a/packages/runtime-common/virtual-network.ts b/packages/runtime-common/virtual-network.ts
index 2011a9a74fc..c0176dea4e4 100644
--- a/packages/runtime-common/virtual-network.ts
+++ b/packages/runtime-common/virtual-network.ts
@@ -132,9 +132,17 @@ export class VirtualNetwork {
   }
 
   /**
-   * Convert a resolved URL back to its registered prefix form when one
-   * matches, e.g. `http://localhost:4201/catalog/foo` → `@cardstack/catalog/foo`.
-   * URLs that don't match any registered prefix are returned as-is.
+   * Convert a URL back to its registered prefix form when one matches,
+   * e.g. `http://localhost:4201/catalog/foo` → `@cardstack/catalog/foo`.
+   *
+   * If the input doesn't directly match any realm-prefix target, and the
+   * input is URL-shaped, chase through any virtual→real URL mapping (e.g.
+   * `https://cardstack.com/base/X` → `http://localhost:4201/base/X`) and
+   * retry the realm-prefix match. This bridges the gap when a realm
+   * prefix is registered against the resolved URL but the caller hands
+   * us the unresolved virtual URL.
+   *
+   * Inputs that match no prefix and no URL mapping are returned as-is.
    */
   unresolveURL(url: string): RealmResourceIdentifier {
     for (let [prefix, target] of this.realmMappings) {
@@ -142,6 +150,22 @@ export class VirtualNetwork {
         return (prefix + url.slice(target.length)) as RealmResourceIdentifier;
       }
     }
+    if (url.startsWith('http://') || url.startsWith('https://')) {
+      let resolved: string | undefined;
+      try {
+        resolved = this.resolveURLMapping(url, 'virtual-to-real');
+      } catch {
+        resolved = undefined;
+      }
+      if (resolved && resolved !== url) {
+        for (let [prefix, target] of this.realmMappings) {
+          if (resolved.startsWith(target)) {
+            return (prefix +
+              resolved.slice(target.length)) as RealmResourceIdentifier;
+          }
+        }
+      }
+    }
     return url as RealmResourceIdentifier;
   }
 
diff --git a/packages/software-factory/realm/kanban-board.test.gts b/packages/software-factory/realm/kanban-board.test.gts
index 811fc15ae56..f08409c66ef 100644
--- a/packages/software-factory/realm/kanban-board.test.gts
+++ b/packages/software-factory/realm/kanban-board.test.gts
@@ -44,7 +44,7 @@ export function runTests() {
               attributes: {},
               meta: {
                 adoptsFrom: {
-                  module: 'https://cardstack.com/base/card-api',
+                  module: '@cardstack/base/card-api',
                   name: 'CardDef',
                 },
               },
diff --git a/packages/software-factory/scripts/smoke-tests/smoke-test-factory-scenarios.ts b/packages/software-factory/scripts/smoke-tests/smoke-test-factory-scenarios.ts
index b15b1aa375e..0503a1274ea 100644
--- a/packages/software-factory/scripts/smoke-tests/smoke-test-factory-scenarios.ts
+++ b/packages/software-factory/scripts/smoke-tests/smoke-test-factory-scenarios.ts
@@ -178,7 +178,7 @@ function buildSpecDocument() {
       },
       meta: {
         adoptsFrom: {
-          module: 'https://cardstack.com/base/spec',
+          module: '@cardstack/base/spec',
           name: 'Spec',
         },
       },
diff --git a/packages/software-factory/scripts/smoke-tests/smoke-test-realm.ts b/packages/software-factory/scripts/smoke-tests/smoke-test-realm.ts
index a03c6158b61..6468ba65d21 100644
--- a/packages/software-factory/scripts/smoke-tests/smoke-test-realm.ts
+++ b/packages/software-factory/scripts/smoke-tests/smoke-test-realm.ts
@@ -67,7 +67,7 @@ const HELLO_SPEC_CARD = {
     },
     meta: {
       adoptsFrom: {
-        module: 'https://cardstack.com/base/spec',
+        module: '@cardstack/base/spec',
         name: 'Spec',
       },
     },
diff --git a/packages/software-factory/tests/helpers/instantiate-test-fixtures.ts b/packages/software-factory/tests/helpers/instantiate-test-fixtures.ts
index 1e666358650..c6f80b77afd 100644
--- a/packages/software-factory/tests/helpers/instantiate-test-fixtures.ts
+++ b/packages/software-factory/tests/helpers/instantiate-test-fixtures.ts
@@ -144,7 +144,7 @@ export function validCardSpecJson(): string {
         },
         meta: {
           adoptsFrom: {
-            module: 'https://cardstack.com/base/spec',
+            module: '@cardstack/base/spec',
             name: 'Spec',
           },
         },
@@ -169,7 +169,7 @@ export function tagsCardSpecJson(): string {
         },
         meta: {
           adoptsFrom: {
-            module: 'https://cardstack.com/base/spec',
+            module: '@cardstack/base/spec',
             name: 'Spec',
           },
         },
diff --git a/packages/software-factory/tests/parse-validation.spec.ts b/packages/software-factory/tests/parse-validation.spec.ts
index 62637d0a3ad..a707085369e 100644
--- a/packages/software-factory/tests/parse-validation.spec.ts
+++ b/packages/software-factory/tests/parse-validation.spec.ts
@@ -93,7 +93,7 @@ test.describe('parse-validation e2e', () => {
           },
           meta: {
             adoptsFrom: {
-              module: 'https://cardstack.com/base/spec',
+              module: '@cardstack/base/spec',
               name: 'Spec',
             },
           },
diff --git a/packages/software-factory/tests/run-parse-in-memory.spec.ts b/packages/software-factory/tests/run-parse-in-memory.spec.ts
index 345d6f2149c..dc4dfd171e0 100644
--- a/packages/software-factory/tests/run-parse-in-memory.spec.ts
+++ b/packages/software-factory/tests/run-parse-in-memory.spec.ts
@@ -68,7 +68,7 @@ function validSpecJson(): string {
         },
         meta: {
           adoptsFrom: {
-            module: 'https://cardstack.com/base/spec',
+            module: '@cardstack/base/spec',
             name: 'Spec',
           },
         },
diff --git a/packages/test-realm-cards/contents/file-query-card.gts b/packages/test-realm-cards/contents/file-query-card.gts
index ac0a709cd35..bb8975aebdd 100644
--- a/packages/test-realm-cards/contents/file-query-card.gts
+++ b/packages/test-realm-cards/contents/file-query-card.gts
@@ -12,7 +12,7 @@ import StringField from 'https://cardstack.com/base/string';
 const fileSearchQuery = {
   filter: {
     type: {
-      module: rri('https://cardstack.com/base/card-api'),
+      module: rri('@cardstack/base/card-api'),
       name: 'FileDef',
     },
   },
diff --git a/packages/vscode-boxel-tools/src/skills.ts b/packages/vscode-boxel-tools/src/skills.ts
index 1ea2d627e28..590c29c812b 100644
--- a/packages/vscode-boxel-tools/src/skills.ts
+++ b/packages/vscode-boxel-tools/src/skills.ts
@@ -384,14 +384,14 @@ export class SkillList extends vscode.TreeItem {
         {
           by: 'title',
           on: {
-            module: 'https://cardstack.com/base/card-api',
+            module: '@cardstack/base/card-api',
             name: 'CardDef',
           },
         },
       ],
       filter: {
         type: {
-          module: 'https://cardstack.com/base/skill',
+          module: '@cardstack/base/skill',
           name: 'Skill',
         },
       },