diff --git a/src/abi/mod.rs b/src/abi/mod.rs
index be2f1cc..6b94921 100644
--- a/src/abi/mod.rs
+++ b/src/abi/mod.rs
@@ -460,7 +460,7 @@ impl AccessPolicy {
 /// with validation and path resolution.
 #[derive(Debug, Clone, Serialize, Deserialize)]
 pub struct SidecarConfig {
-    /// Storage backend: "sqlite" or "json".
+    /// Storage backend: "sqlite" (default) or "postgres"/"postgresql".
     pub storage: String,
     /// File path for the sidecar database.
     pub path: String,
diff --git a/src/codegen/overlay.rs b/src/codegen/overlay.rs
index 893231e..596fe90 100644
--- a/src/codegen/overlay.rs
+++ b/src/codegen/overlay.rs
@@ -83,21 +83,29 @@ pub enum SqlDialect {
 impl SqlDialect {
     /// Map a `[sidecar].storage` value to a dialect. `sqlite` →
     /// [`SqlDialect::Sqlite`]; `postgres`/`postgresql` →
-    /// [`SqlDialect::Postgres`]. `json` and unknown values are rejected
-    /// (the previous behaviour silently emitted SQLite DDL regardless,
-    /// V-L2-F1). The JSON store is tracked separately by #112.
+    /// [`SqlDialect::Postgres`]. Every other value is rejected rather than
+    /// silently emitting SQLite DDL regardless of the configured store
+    /// (V-L2-F1).
+    ///
+    /// This is the single source of truth for "is this a supported sidecar
+    /// storage value?": [`crate::manifest::validate_manifest`] calls it so
+    /// `validate`, `doctor`, and `generate` cannot disagree on the closed
+    /// set.
+    ///
+    /// V-L2-F2 (#112): a JSON sidecar store was evaluated here and dropped
+    /// rather than implemented. There is no storage-abstraction layer to
+    /// host a second runtime backend yet (provenance, temporal, drift, and
+    /// gc are all SQLite-specific), so leaving it advertised-but-rejected
+    /// was worse than removing it. If a flat-file store is wanted later it
+    /// should be designed against a real storage trait and re-added to this
+    /// match — until then it is just another unsupported value.
     pub fn from_storage(storage: &str) -> anyhow::Result<Self> {
         match storage.to_lowercase().as_str() {
             "sqlite" => Ok(SqlDialect::Sqlite),
             "postgres" | "postgresql" => Ok(SqlDialect::Postgres),
-            "json" => anyhow::bail!(
-                "[sidecar].storage = \"json\" is not implemented (it previously \
-                 emitted SQLite DDL silently). Use \"sqlite\". The JSON sidecar \
-                 store is tracked by hyperpolymath/verisimiser#112."
-            ),
             other => anyhow::bail!(
-                "unknown [sidecar].storage {other:?}; supported: \"sqlite\" \
-                 (\"postgres\" for a PostgreSQL sidecar; \"json\" is #112)."
+                "unsupported [sidecar].storage {other:?}; supported backends \
+                 are \"sqlite\" (default) and \"postgres\"/\"postgresql\"."
             ),
         }
     }
@@ -879,10 +887,18 @@ mod tests {
             SqlDialect::from_storage("PostgreSQL").unwrap(),
             SqlDialect::Postgres
         );
+        // V-L2-F2 (#112): the JSON store was dropped, not implemented, so
+        // `json` is now rejected exactly like any other unsupported value —
+        // no special-case "coming soon" text and no #112 pointer.
         let json_err = SqlDialect::from_storage("json").unwrap_err().to_string();
         assert!(
-            json_err.contains("not implemented") && json_err.contains("#112"),
-            "json must be rejected with the #112 pointer, got: {json_err}"
+            json_err.contains("unsupported") && json_err.contains("sqlite"),
+            "json must be rejected as unsupported and list the supported \
+             backends, got: {json_err}"
+        );
+        assert!(
+            !json_err.contains("#112") && !json_err.contains("not implemented"),
+            "a dropped backend must not be advertised as tracked/coming, got: {json_err}"
         );
         assert!(SqlDialect::from_storage("mariadb").is_err());
     }
diff --git a/src/gc.rs b/src/gc.rs
index 16fb4de..d623acf 100644
--- a/src/gc.rs
+++ b/src/gc.rs
@@ -309,7 +309,10 @@ mod tests {
 
     #[test]
     fn gc_rejects_non_sqlite_backend() {
-        let m = fixture("/dev/null", RetentionConfig::default(), "json");
+        // `postgres` is a valid generate-time dialect, but gc is SQLite-only
+        // and must refuse rather than silently no-op. (The `json` value was
+        // dropped as a storage option entirely in V-L2-F2 / #112.)
+        let m = fixture("/dev/null", RetentionConfig::default(), "postgres");
         let err = run_gc(&m, true).unwrap_err();
         assert!(
             err.to_string().contains("only supports the SQLite sidecar"),
diff --git a/src/main.rs b/src/main.rs
index c5df959..eae66ab 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -209,9 +209,10 @@ fn main() -> Result<()> {
             // Create output directory.
             std::fs::create_dir_all(&output)?;
 
-            // The sidecar DDL dialect follows [sidecar].storage. This
-            // rejects `json` (tracked by #112) instead of silently
-            // emitting SQLite DDL for a non-SQLite store (V-L2-F1).
+            // The sidecar DDL dialect follows [sidecar].storage. Unknown or
+            // unsupported values are rejected here (and earlier by
+            // `validate`) instead of silently emitting SQLite DDL for a
+            // non-SQLite store (V-L2-F1 / V-L2-F2).
             let dialect = codegen::overlay::SqlDialect::from_storage(&m.sidecar.storage)?;
 
             // Generate sidecar overlay schema. Errors here surface invalid
diff --git a/src/manifest/mod.rs b/src/manifest/mod.rs
index 3659e5b..8e3fc2d 100644
--- a/src/manifest/mod.rs
+++ b/src/manifest/mod.rs
@@ -279,11 +279,14 @@ mod octad_tests {
 /// temporal versions, and access policies. It never writes to your target database.
 #[derive(Debug, Clone, Serialize, Deserialize)]
 pub struct SidecarConfig {
-    /// Storage backend for the sidecar. `"sqlite"` (default) is the only
-    /// implemented store; `"postgres"`/`"postgresql"` selects the
-    /// PostgreSQL DDL dialect. `"json"` is **not implemented** and is
-    /// rejected at `generate` time — tracked by #112 (V-L2-F2). The
-    /// dialect mapping lives in `codegen::overlay::SqlDialect`.
+    /// Storage backend for the sidecar. The supported set is closed:
+    /// `"sqlite"` (default) is the fully-featured runtime store used by
+    /// `generate`, `drift`, and `gc`; `"postgres"`/`"postgresql"` selects
+    /// the PostgreSQL DDL dialect emitted by `generate`. Any other value is
+    /// rejected — `validate`/`doctor` flag it up front via the
+    /// `sidecar-storage-supported` check, and `generate` refuses it rather
+    /// than silently emitting SQLite DDL. The canonical mapping lives in
+    /// [`crate::codegen::overlay::SqlDialect::from_storage`].
     #[serde(default = "default_sidecar_storage")]
     pub storage: String,
 
@@ -394,6 +397,78 @@ mod validate_manifest_tests {
         assert_eq!(failed, vec!["schema-source-exists"]);
     }
 
+    /// V-L2-F2 (#112): a dropped/unsupported `[sidecar].storage` value
+    /// (here the removed `json` store) must fail the
+    /// `sidecar-storage-supported` check at validate time, not slip
+    /// through to `generate`. Other checks still run independently.
+    #[test]
+    fn unsupported_storage_fails_storage_check() {
+        let dir = tempfile::tempdir().expect("tempdir");
+        let path = dir.path().join("verisimiser.toml");
+        let sidecar_path = dir.path().join("sidecar.db");
+        let body = format!(
+            "[project]\n\
+             name = \"test\"\n\
+             [database]\n\
+             backend = \"sqlite\"\n\
+             [sidecar]\n\
+             storage = \"json\"\n\
+             path = \"{}\"\n",
+            sidecar_path.display().to_string().replace('\\', "/")
+        );
+        std::fs::write(&path, body).expect("write");
+
+        let report = validate_manifest(path.to_str().unwrap());
+        assert!(!report.passed, "json storage must not validate");
+        let failed: Vec<&str> = report
+            .checks
+            .iter()
+            .filter(|c| !c.passed)
+            .map(|c| c.name.as_str())
+            .collect();
+        assert_eq!(
+            failed,
+            vec!["sidecar-storage-supported"],
+            "only the storage check should fail; checks: {:?}",
+            report.checks
+        );
+    }
+
+    /// The PostgreSQL dialect remains a supported `storage` value (it
+    /// selects the postgres DDL for `generate`), so a postgres sidecar
+    /// must still pass validation.
+    #[test]
+    fn postgres_storage_passes_storage_check() {
+        let dir = tempfile::tempdir().expect("tempdir");
+        let path = dir.path().join("verisimiser.toml");
+        let sidecar_path = dir.path().join("sidecar.db");
+        let body = format!(
+            "[project]\n\
+             name = \"test\"\n\
+             [database]\n\
+             backend = \"postgresql\"\n\
+             [sidecar]\n\
+             storage = \"postgres\"\n\
+             path = \"{}\"\n",
+            sidecar_path.display().to_string().replace('\\', "/")
+        );
+        std::fs::write(&path, body).expect("write");
+
+        let report = validate_manifest(path.to_str().unwrap());
+        assert!(
+            report.passed,
+            "postgres storage must validate; checks: {:?}",
+            report.checks
+        );
+        assert!(
+            report
+                .checks
+                .iter()
+                .any(|c| c.name == "sidecar-storage-supported" && c.passed),
+            "the storage-supported check must run and pass"
+        );
+    }
+
     /// A malformed manifest must fail `manifest-loads` and stop further
     /// checks (because the rest depend on having a parsed manifest).
     #[test]
@@ -621,6 +696,7 @@ enable-constraints = {enable_constraints}
 enable-simulation = {enable_simulation}
 
 [sidecar]
+# storage backend: "sqlite" (default) or "postgres"
 storage = "{sidecar_storage}"
 path = "{sidecar_path}"
 
@@ -734,6 +810,10 @@ impl ValidationReport {
 ///    set, the file at that path is readable.
 /// 3. **`sidecar-path-writable`** — the parent directory of
 ///    `[sidecar].path` is writable (or createable).
+/// 4. **`sidecar-storage-supported`** — `[sidecar].storage` is one of the
+///    supported backends (`sqlite`, `postgres`/`postgresql`). Reuses the
+///    same mapping `generate` uses so a manifest that validates cannot
+///    then fail at generate time on an unsupported store. V-L2-F2 (#112).
 ///
 /// Out of scope here: V-L2-E1 backend/target_db conflict (own issue),
 /// target-DB reachability (needs live connection).
@@ -820,6 +900,29 @@ pub fn validate_manifest(path: &str) -> ValidationReport {
                 )),
             });
         }
+
+        // 4. Sidecar storage backend is one we support. Reuses the same
+        //    mapping `generate` uses (codegen::overlay::SqlDialect) so a
+        //    manifest that validates here cannot then fail at generate
+        //    time on an unsupported store — and so a dropped backend
+        //    (e.g. json, V-L2-F2 #112) is rejected consistently at
+        //    validate, doctor, and generate.
+        let storage_check =
+            match crate::codegen::overlay::SqlDialect::from_storage(&m.sidecar.storage) {
+                Ok(_) => ValidationCheck {
+                    name: "sidecar-storage-supported".to_string(),
+                    description: "[sidecar].storage is a supported backend".to_string(),
+                    passed: true,
+                    detail: None,
+                },
+                Err(e) => ValidationCheck {
+                    name: "sidecar-storage-supported".to_string(),
+                    description: "[sidecar].storage is a supported backend".to_string(),
+                    passed: false,
+                    detail: Some(e.to_string()),
+                },
+            };
+        checks.push(storage_check);
     }
 
     let passed = checks.iter().all(|c| c.passed);