diff --git a/doc/SPEC-implementation.md b/doc/SPEC-implementation.md
index 09df2d1c08e..b082bc33b68 100644
--- a/doc/SPEC-implementation.md
+++ b/doc/SPEC-implementation.md
@@ -642,7 +642,7 @@ The approved term set is:
 
 Core owns the closed, versioned host-feature keys `apps.named_mcp_gateways` and `apps.access_profiles`. Only the canonical `paperclipai.paperclip-ee` plugin may declare them in `PaperclipPluginManifestV1.hostFeatures`, and only a stored plugin record in `ready` state enables its valid declaration. Missing, installed, disabled, error, upgrade-pending, uninstalled, malformed, or non-canonical providers resolve to an empty feature set.
 
-The server injects the non-sensitive effective feature snapshot into both static and Vite-served HTML before React starts, and exposes the same snapshot through an authenticated API for lifecycle revalidation. UI visibility is advisory; server routes remain authoritative. Named-gateway management, token, metadata, public, and ID-based MCP routes require `apps.named_mcp_gateways`. Profile administration routes require `apps.access_profiles`. Unavailable management routes return `404` with `code: "feature_unavailable"`.
+The server injects the non-sensitive effective feature snapshot into both static and Vite-served HTML before React starts, and exposes the same snapshot through an authenticated API for lifecycle revalidation. UI visibility is advisory; server routes remain authoritative. Named-gateway management, token, metadata, public, and ID-based MCP routes require `apps.named_mcp_gateways`. Profile administration routes require `apps.access_profiles`. Unavailable management routes return `404` with the flat body `{ "error": "Feature unavailable", "code": "feature_unavailable", "feature": "<host-feature-key>" }`.
 
 Core profile list/effective reads, internal tool-gateway sessions, and runtime policy enforcement stay available in all editions. Feature disable and plugin uninstall do not delete gateway, profile, binding, entry, token, or policy rows; returning the canonical provider to `ready` restores the management surfaces over the existing data.
 
diff --git a/server/src/__tests__/error-handler.test.ts b/server/src/__tests__/error-handler.test.ts
index cfd65a23a2e..a37d795415f 100644
--- a/server/src/__tests__/error-handler.test.ts
+++ b/server/src/__tests__/error-handler.test.ts
@@ -112,6 +112,25 @@ describe("errorHandler", () => {
     expect(res.__errorContext).toBeUndefined();
   });
 
+  it("flattens feature-unavailable metadata into the stable response shape", () => {
+    const req = makeReq();
+    const res = makeRes();
+    const next = vi.fn() as unknown as NextFunction;
+    const err = new HttpError(404, "Feature unavailable", {
+      code: "feature_unavailable",
+      feature: "apps.access_profiles",
+    });
+
+    errorHandler(err, req, res, next);
+
+    expect(res.status).toHaveBeenCalledWith(404);
+    expect(res.json).toHaveBeenCalledWith({
+      error: "Feature unavailable",
+      code: "feature_unavailable",
+      feature: "apps.access_profiles",
+    });
+  });
+
   it("records responsible-user denial codes on the active agent run", () => {
     const db = { marker: "db" };
     const req = {
diff --git a/server/src/__tests__/tool-access-service.test.ts b/server/src/__tests__/tool-access-service.test.ts
index 2cd67266e8c..ce4b1488b85 100644
--- a/server/src/__tests__/tool-access-service.test.ts
+++ b/server/src/__tests__/tool-access-service.test.ts
@@ -534,10 +534,10 @@ describeEmbeddedPostgres("tool access service", () => {
     ];
     for (const response of gatedResponses) {
       expect(response.status).toBe(404);
-      expect(response.body).toMatchObject({
+      expect(response.body).toEqual({
         error: "Feature unavailable",
         code: "feature_unavailable",
-        details: { code: "feature_unavailable", feature: "apps.access_profiles" },
+        feature: "apps.access_profiles",
       });
     }
 
diff --git a/server/src/__tests__/tool-gateway.test.ts b/server/src/__tests__/tool-gateway.test.ts
index 26147d1b4a3..d24b0471772 100644
--- a/server/src/__tests__/tool-gateway.test.ts
+++ b/server/src/__tests__/tool-gateway.test.ts
@@ -584,7 +584,7 @@ describeEmbeddedPostgres("tool gateway acceptance", () => {
 
     for (const response of responses) {
       expect(response.status).toBe(404);
-      expect(response.body).toMatchObject({
+      expect(response.body).toEqual({
         error: "Feature unavailable",
         code: "feature_unavailable",
         feature: "apps.named_mcp_gateways",
diff --git a/server/src/middleware/error-handler.ts b/server/src/middleware/error-handler.ts
index 0a4aa1a1703..4df7e1d7526 100644
--- a/server/src/middleware/error-handler.ts
+++ b/server/src/middleware/error-handler.ts
@@ -91,6 +91,7 @@ export function errorHandler(
       : null;
     const redactedSkillPolicyDenial = isRedactedSkillPolicyDenial(details);
     const workspaceRepairPreconditionFailure = details?.code === "workspace_repair_precondition_failed";
+    const featureUnavailable = details?.code === "feature_unavailable";
     const structuredConnectionError = new Set([
       "user_authorization_required",
       "grant_revoked",
@@ -113,6 +114,7 @@ export function errorHandler(
     res.status(err.status).json({
       error: err.message,
       ...(typeof details?.code === "string" ? { code: details.code } : {}),
+      ...(featureUnavailable && typeof details?.feature === "string" ? { feature: details.feature } : {}),
       ...(redactedSkillPolicyDenial && typeof details?.reason === "string" ? { reason: details.reason } : {}),
       ...(workspaceRepairPreconditionFailure && typeof details?.reason === "string" ? { reason: details.reason } : {}),
       ...(workspaceRepairPreconditionFailure && typeof details?.repairPhase === "string"
@@ -124,7 +126,7 @@ export function errorHandler(
       ...(structuredConnectionError && details?.connection ? { connection: details.connection } : {}),
       ...(structuredConnectionError && details?.subject ? { subject: details.subject } : {}),
       ...(structuredConnectionError && typeof details?.grantId === "string" ? { grantId: details.grantId } : {}),
-      ...(!redactedSkillPolicyDenial && !workspaceRepairPreconditionFailure && err.details
+      ...(!redactedSkillPolicyDenial && !workspaceRepairPreconditionFailure && !featureUnavailable && err.details
         ? { details: err.details }
         : {}),
     });