diff --git a/.claude/rules/sveltekit.md b/.claude/rules/sveltekit.md
index 058816523..ffdcbaf6c 100644
--- a/.claude/rules/sveltekit.md
+++ b/.claude/rules/sveltekit.md
@@ -84,12 +84,12 @@ group them as an object rather than flattening to top-level keys.
 Apply default values at this boundary so the page component typically does not need to handle `undefined`.
 
 ```typescript
-// Bad: flat, scattered across top-level keys
-atcoder_username: user?.atCoderAccount?.handle ?? '',
-atcoder_validationcode: user?.atCoderAccount?.validationCode ?? '',
-is_validated: user?.atCoderAccount?.isValidated ?? false,
+// Bad: flat top-level keys (legacy snake_case naming, scattered fields)
+atcoder_handle: user?.atCoderAccount?.handle ?? '',
+atcoder_validation_code: user?.atCoderAccount?.validationCode ?? '',
+atcoder_is_validated: user?.atCoderAccount?.isValidated ?? false,
 
-// Good: grouped by model, defaults absorbed here
+// Good: grouped by model with camelCase; defaults absorbed here
 atCoderAccount: {
   handle:         user?.atCoderAccount?.handle         ?? '',
   validationCode: user?.atCoderAccount?.validationCode ?? '',
diff --git a/.claude/rules/testing-e2e.md b/.claude/rules/testing-e2e.md
index 9c394361a..efbcaa1ab 100644
--- a/.claude/rules/testing-e2e.md
+++ b/.claude/rules/testing-e2e.md
@@ -83,10 +83,10 @@ const toggleInput = page.locator('input[aria-label="<aria-label value>"]');
 const toggleLabel = page.locator('label:has(input[aria-label="<aria-label value>"])');
 
 await toggleLabel.click();
-await expect(toggleInput).toBeChecked({ checked: true });
+await expect(toggleInput).toBeChecked();
 ```
 
-The same pattern applies to any Flowbite component that visually overlays its native input (e.g. `Checkbox`, `Radio`).
+The same pattern may apply to similar Flowbite components that visually overlay their native input (e.g. `Checkbox`, `Radio`). Verify the component structure before applying this workaround.
 
 ## Strict Mode: Scope Locators to the Content Area
 
@@ -97,7 +97,7 @@ When the navbar and page body both contain a link or button with the same text (
 await page.getByRole('link', { name: 'グレード投票' }).click();
 
 // Good: scoped to page content only
-await page.locator('.container').locator('nav').getByRole('link', { name: 'グレード投票' }).click();
+await page.locator('.container nav').getByRole('link', { name: 'グレード投票' }).click();
 await page.locator('.container').getByRole('link', { name: 'ログイン' }).click();
 ```
 
diff --git a/.claude/rules/testing.md b/.claude/rules/testing.md
index 24f663018..ca79c1e07 100644
--- a/.claude/rules/testing.md
+++ b/.claude/rules/testing.md
@@ -105,7 +105,7 @@ Extract `mockFindUnique`, `mockFindMany`, and `mockCount` as the standard trio f
 
 ### Cleanup for Integration Tests and Tests with Real Side Effects
 
-This does not apply to standard service layer unit tests that use Prisma mocks.
+> **Note:** This does not apply to standard service layer unit tests that use Prisma mocks.
 
 If a test performs real DB mutations, file system changes, external API calls, or other stateful side effects that persist beyond the test (e.g., integration tests, seed scripts), wrap assertions in `try/finally` — a failing assertion skips cleanup and contaminates later tests:
 
@@ -118,8 +118,6 @@ try {
 }
 ```
 
-This is not needed for standard service unit tests that use Prisma mocks.
-
 ### File Split for Testability
 
 When a service file mixes DB operations and pure functions, split it into two files:
@@ -135,7 +133,7 @@ E2E tests are complementary to, not a substitute for, unit tests. Add Vitest uni
 
 You may omit a component-level Vitest test when **both** conditions hold:
 
-1. The component is template-only (no logic beyond prop bindings and simple `{#if}`/`{#each}` blocks that only render — no inline function calls, ternaries with side effects, derived computations, or nested logic)
+1. The component is template-only (no logic beyond prop bindings and simple `{#if}`/`{#each}` blocks that only render — no inline function calls, ternaries with complex conditional logic, derived computations, or nested logic)
 2. The component's rendering paths are covered by E2E tests
 
 When a component contains extracted logic (e.g. derived values, event handlers, utility calls), add unit tests for that logic in the nearest `utils/` file instead of testing the component directly.
diff --git a/.env.example b/.env.example
index 3f811d189..1896accd0 100644
--- a/.env.example
+++ b/.env.example
@@ -1,3 +1,4 @@
 # AtCoder affiliation confirmation API endpoint (NoviSteps organization crawler)
+# WARNING: Do NOT commit the actual endpoint URL. Set it in your local .env file.
 # See team documentation for the actual URL.
 CONFIRM_API_URL=https://your-confirm-api-endpoint.example.com/confirm
diff --git a/e2e/votes.spec.ts b/e2e/votes.spec.ts
index 17bc86914..5fa1f0685 100644
--- a/e2e/votes.spec.ts
+++ b/e2e/votes.spec.ts
@@ -131,11 +131,6 @@ test.describe('vote detail page (/votes/[slug])', () => {
       const isUnverified = await unverifiedMessage.isVisible();
       test.skip(isUnverified, 'test user is not AtCoder-verified');
 
-      // Explicit check: voteForm is already guaranteed visible by the or() wait above,
-      // but this documents the expected state for verified users.
-      await expect(voteForm).toBeVisible({
-        timeout: TIMEOUT,
-      });
       // The grade buttons should include Q11 (11Q)
       await expect(page.getByRole('button', { name: '11Q' })).toBeVisible({ timeout: TIMEOUT });
     });
diff --git a/src/features/votes/actions/vote_actions.ts b/src/features/votes/actions/vote_actions.ts
index 41ebd438c..679f4a288 100644
--- a/src/features/votes/actions/vote_actions.ts
+++ b/src/features/votes/actions/vote_actions.ts
@@ -28,7 +28,13 @@ export const voteAbsoluteGrade = async ({
     });
   }
 
-  if (!locals.user?.is_validated) {
+  if (!locals.user) {
+    return fail(INTERNAL_SERVER_ERROR, {
+      message: 'ユーザー情報の取得に失敗しました。',
+    });
+  }
+
+  if (!locals.user.is_validated) {
     return fail(FORBIDDEN, {
       message: 'AtCoderアカウントの認証が必要です。',
     });
diff --git a/src/routes/problems/+page.svelte b/src/routes/problems/+page.svelte
index ecf9aef2a..4f618008b 100644
--- a/src/routes/problems/+page.svelte
+++ b/src/routes/problems/+page.svelte
@@ -20,7 +20,7 @@
 
   let { data } = $props();
 
-  let taskResults: TaskResults = $derived(data.taskResults.sort(compareByContestIdAndTaskId));
+  const taskResults: TaskResults = $derived(data.taskResults.sort(compareByContestIdAndTaskId));
 
   const isAdmin = $derived(data.isAdmin);
   const isLoggedIn = $derived(data.isLoggedIn);
diff --git a/src/routes/users/edit/+page.server.ts b/src/routes/users/edit/+page.server.ts
index 77e2f44a9..c61caa447 100644
--- a/src/routes/users/edit/+page.server.ts
+++ b/src/routes/users/edit/+page.server.ts
@@ -136,17 +136,12 @@ export const actions: Actions = {
     try {
       await userService.deleteUser(username);
       locals.auth.setSession(null); // remove cookie
-
-      return {
-        success: true,
-        username,
-        message_type: 'green',
-        message: 'Successfully deleted.',
-      };
     } catch (error) {
       console.error('Failed to delete user account', error);
       return fail(INTERNAL_SERVER_ERROR, { message: 'Failed to delete account.' });
     }
+
+    redirect(302, '/login');
   },
 };