diff --git a/apps/code/src/main/services/mcp-proxy/service.ts b/apps/code/src/main/services/mcp-proxy/service.ts
index 07ffd9241..1cf267355 100644
--- a/apps/code/src/main/services/mcp-proxy/service.ts
+++ b/apps/code/src/main/services/mcp-proxy/service.ts
@@ -183,10 +183,11 @@ export class McpProxyService {
         const buf = Buffer.from(await response.arrayBuffer());
         const bodyText = buf.toString("utf8");
 
-        if (this.isAuthErrorBody(bodyText)) {
-          log.warn("MCP auth error in body — refreshing token and retrying", {
+        if (this.isAuthErrorBody(bodyText, response.status)) {
+          log.warn("MCP auth failure — refreshing token and retrying", {
             id,
             url,
+            status: response.status,
           });
           await this.authService.refreshAccessToken();
           response = await this.authService.authenticatedFetch(
@@ -235,10 +236,17 @@ export class McpProxyService {
     }
   }
 
-  private isAuthErrorBody(bodyText: string): boolean {
-    return (
+  private isAuthErrorBody(bodyText: string, status: number): boolean {
+    if (
       bodyText.includes('"authentication_failed"') ||
       bodyText.includes('"authentication_error"')
+    ) {
+      return true;
+    }
+    if (status < 400) return false;
+    return (
+      bodyText.includes("Invalid API key") ||
+      bodyText.includes("Authentication failed")
     );
   }
 
diff --git a/apps/code/src/renderer/api/fetcher.test.ts b/apps/code/src/renderer/api/fetcher.test.ts
index 62a510620..b74b32409 100644
--- a/apps/code/src/renderer/api/fetcher.test.ts
+++ b/apps/code/src/renderer/api/fetcher.test.ts
@@ -13,15 +13,15 @@ describe("buildApiFetcher", () => {
     status: 200,
     json: () => Promise.resolve(data),
   });
-  const err = (status: number) => {
+  const err = (status: number, body: object = { error: status }) => {
     const response = {
       ok: false,
       status,
       statusText: `Error ${status}`,
-      json: () => Promise.resolve({ error: status }),
+      json: () => Promise.resolve(body),
       clone: () => ({
         ...response,
-        text: () => Promise.resolve(`Error ${status}`),
+        text: () => Promise.resolve(JSON.stringify(body)),
       }),
     };
     return response;
@@ -63,10 +63,10 @@ describe("buildApiFetcher", () => {
     );
   });
 
-  it("does not retry on non-401 errors", async () => {
+  it("does not retry on 403 without authentication_failed body", async () => {
     const getAccessToken = vi.fn().mockResolvedValue("token");
     const refreshAccessToken = vi.fn().mockResolvedValue("new-token");
-    mockFetch.mockResolvedValueOnce(err(403));
+    mockFetch.mockResolvedValueOnce(err(403, { detail: "Permission denied." }));
 
     const fetcher = buildApiFetcher({ getAccessToken, refreshAccessToken });
 
@@ -75,6 +75,42 @@ describe("buildApiFetcher", () => {
     expect(refreshAccessToken).not.toHaveBeenCalled();
   });
 
+  it("retries with a fresh token on 403 with authentication_failed body", async () => {
+    const getAccessToken = vi.fn().mockResolvedValue("stale-token");
+    const refreshAccessToken = vi.fn().mockResolvedValue("fresh-token");
+    mockFetch
+      .mockResolvedValueOnce(
+        err(403, {
+          type: "authentication_error",
+          code: "authentication_failed",
+          detail: "Invalid access token.",
+        }),
+      )
+      .mockResolvedValueOnce(ok());
+
+    const fetcher = buildApiFetcher({ getAccessToken, refreshAccessToken });
+    const response = await fetcher.fetch(mockInput);
+
+    expect(response.ok).toBe(true);
+    expect(refreshAccessToken).toHaveBeenCalledTimes(1);
+    expect(mockFetch.mock.calls[1][1].headers.get("Authorization")).toBe(
+      "Bearer fresh-token",
+    );
+  });
+
+  it("does not retry on other 4xx errors", async () => {
+    const refreshAccessToken = vi.fn().mockResolvedValue("new-token");
+    mockFetch.mockResolvedValueOnce(err(400, { detail: "Bad request." }));
+
+    const fetcher = buildApiFetcher({
+      getAccessToken: vi.fn().mockResolvedValue("token"),
+      refreshAccessToken,
+    });
+
+    await expect(fetcher.fetch(mockInput)).rejects.toThrow("[400]");
+    expect(refreshAccessToken).not.toHaveBeenCalled();
+  });
+
   it("throws when the retry still returns 401", async () => {
     const getAccessToken = vi.fn().mockResolvedValue("token-1");
     const refreshAccessToken = vi.fn().mockResolvedValue("token-2");
diff --git a/apps/code/src/renderer/api/fetcher.ts b/apps/code/src/renderer/api/fetcher.ts
index 74a45e26d..2978f0b1c 100644
--- a/apps/code/src/renderer/api/fetcher.ts
+++ b/apps/code/src/renderer/api/fetcher.ts
@@ -52,12 +52,25 @@ export const buildApiFetcher: (config: {
     }
   };
 
+  const isAuthFailure = async (response: Response): Promise<boolean> => {
+    if (response.status === 401) return true;
+    if (response.status !== 403) return false;
+    try {
+      const body = await response.clone().json();
+      return (
+        body?.code === "authentication_failed" ||
+        body?.type === "authentication_error"
+      );
+    } catch {
+      return false;
+    }
+  };
+
   return {
     fetch: async (input) => {
       let response = await makeRequest(input, await config.getAccessToken());
 
-      // Retry once on 401 after asking main for a fresh valid token again.
-      if (!response.ok && response.status === 401) {
+      if (!response.ok && (await isAuthFailure(response))) {
         try {
           response = await makeRequest(
             input,