fix: preserve MCP passthrough account context

api/mcp.ts

@@ -42,12 +42,14 @@ type ResponseLike = {
   on(event: 'close' | 'finish', listener: () => void): void;
 } & ServerResponse;
 
+const UUID = /^[0-9a-f]{8}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{12}$/i;
+
 function setCorsHeaders(res: ResponseLike): void {
   res.setHeader('Access-Control-Allow-Origin', '*');
   res.setHeader('Access-Control-Allow-Methods', 'POST, OPTIONS');
   res.setHeader(
     'Access-Control-Allow-Headers',
-    'Content-Type, Authorization, MCP-Protocol-Version, Mcp-Method, Mcp-Name, Mcp-Session-Id',
+    'Content-Type, Authorization, X-Account-ID, X-T49-Credential-Type, MCP-Protocol-Version, Mcp-Method, Mcp-Name, Mcp-Session-Id',
   );
 }
 
@@ -477,10 +479,52 @@ export default async function handler(
       return;
     }
 
+    const requestedAccountId =
+      resolvedAuth.scheme === 'Token'
+        ? getHeaderValue(req.headers['x-account-id'])
+        : undefined;
+    const credentialType =
+      resolvedAuth.scheme === 'Token'
+        ? getHeaderValue(req.headers['x-t49-credential-type'])
+        : undefined;
+    if (credentialType && credentialType !== 'bearer') {
+      res.status(400).json({
+        error: 'Bad Request',
+        message: 'X-T49-Credential-Type is invalid.',
+      });
+      logLifecycle('mcp.request.complete', requestId, {
+        reason: 'invalid_credential_type',
+      });
+      return;
+    }
+    if (requestedAccountId && !UUID.test(requestedAccountId)) {
+      res.status(400).json({
+        error: 'Bad Request',
+        message: 'X-Account-ID must be a UUID.',
+      });
+      logLifecycle('mcp.request.complete', requestId, {
+        reason: 'invalid_account_id',
+      });
+      return;
+    }
+    if (credentialType === 'bearer' && !requestedAccountId) {
+      res.status(400).json({
+        error: 'Bad Request',
+        message:
+          'X-Account-ID is required for an account-scoped bearer credential.',
+      });
+      logLifecycle('mcp.request.complete', requestId, {
+        reason: 'missing_account_id',
+      });
+      return;
+    }
+
     const configuredApiToken = process.env.T49_API_TOKEN?.trim();
     const configuredClientSecret = process.env.T49_MCP_CLIENT_SECRET?.trim();
     let resolvedTerminal49Auth: ResolvedTerminal49Auth = {
-      apiToken: callerToken,
+      apiToken:
+        credentialType === 'bearer' ? `Bearer ${callerToken}` : callerToken,
+      accountId: credentialType === 'bearer' ? requestedAccountId : undefined,
       authSource: resolvedAuth.source ?? 'authorization',
     };
 

packages/mcp/tests/api-handler.test.ts

@@ -192,6 +192,80 @@ describe('api/mcp handler lifecycle', () => {
     expect(mockState.serverCreateArgs[0]?.apiToken).toBe('token-scheme-value');
   });
 
+  it('does not forward account context from an ordinary API key', async () => {
+    const { default: handler } = await import('../../../api/mcp.ts');
+    const req = createRequest({
+      headers: {
+        host: 'localhost',
+        authorization: 'Token token-scheme-value',
+        'x-account-id': 'f5e2f70e-2de8-4456-8596-db40e617b808',
+      },
+    });
+    const res = new MockResponse();
+
+    await handler(req as any, res as any);
+
+    expect(mockState.serverCreateArgs[0]).toMatchObject({
+      apiToken: 'token-scheme-value',
+      accountId: undefined,
+    });
+  });
+
+  it('forwards an account-scoped caller bearer without exposing it to OAuth resolution', async () => {
+    const { default: handler } = await import('../../../api/mcp.ts');
+    const accountId = 'f5e2f70e-2de8-4456-8596-db40e617b808';
+    const req = createRequest({
+      headers: {
+        host: 'localhost',
+        authorization: 'Token token-scheme-value',
+        'x-account-id': accountId,
+        'x-t49-credential-type': 'bearer',
+      },
+    });
+    const res = new MockResponse();
+
+    await handler(req as any, res as any);
+
+    expect(mockState.serverCreateArgs[0]).toMatchObject({
+      apiToken: 'Bearer token-scheme-value',
+      accountId,
+    });
+  });
+
+  it('requires account context for a caller bearer', async () => {
+    const { default: handler } = await import('../../../api/mcp.ts');
+    const req = createRequest({
+      headers: {
+        host: 'localhost',
+        authorization: 'Token token-scheme-value',
+        'x-t49-credential-type': 'bearer',
+      },
+    });
+    const res = new MockResponse();
+
+    await handler(req as any, res as any);
+
+    expect(res.statusCode).toBe(400);
+    expect(mockState.servers).toHaveLength(0);
+  });
+
+  it('rejects malformed account context before constructing a server', async () => {
+    const { default: handler } = await import('../../../api/mcp.ts');
+    const req = createRequest({
+      headers: {
+        host: 'localhost',
+        authorization: 'Token token-scheme-value',
+        'x-account-id': 'not-an-account-id',
+      },
+    });
+    const res = new MockResponse();
+
+    await handler(req as any, res as any);
+
+    expect(res.statusCode).toBe(400);
+    expect(mockState.servers).toHaveLength(0);
+  });
+
   it('allows requests without Host header when allow-list is not configured', async () => {
     const { default: handler } = await import('../../../api/mcp.ts');
     const req = createRequest({