fix(#829): gate claudex and close branch coverage gaps

packages/mosaic/src/mutator-gate/mutator-gate.acceptance.spec.ts

@@ -244,6 +244,52 @@ describe('whole mutator-class lease gate', () => {
     }
   });
 
+  test('lease and tool validation failures remain fail-closed at the broker boundary', async () => {
+    const { socket } = await startBroker();
+    const sessionId = await register(socket);
+    const baseRequest = {
+      action: 'begin_verification',
+      session_id: sessionId,
+      runtime_generation: 1,
+      runtime: 'claude',
+      ttl_seconds: 300,
+      binding: binding(),
+    };
+
+    expect(await request(socket, { ...baseRequest, runtime: 'codex' })).toMatchObject({
+      ok: false,
+      code: 'INVALID_RUNTIME',
+    });
+    expect(
+      await request(socket, { ...baseRequest, binding: { ...binding(), h_source: 'bad' } }),
+    ).toMatchObject({
+      ok: false,
+      code: 'INVALID_BINDING',
+    });
+    expect(await request(socket, { ...baseRequest, ttl_seconds: 0 })).toMatchObject({
+      ok: false,
+      code: 'INVALID_LEASE_TTL',
+    });
+    expect(
+      await request(socket, {
+        action: 'authorize_tool',
+        session_id: sessionId,
+        runtime_generation: 1,
+        runtime: 'codex',
+        tool_name: 'Read',
+      }),
+    ).toMatchObject({ ok: false, code: 'INVALID_RUNTIME' });
+    expect(
+      await request(socket, {
+        action: 'authorize_tool',
+        session_id: sessionId,
+        runtime_generation: 1,
+        runtime: 'claude',
+        tool_name: 'x'.repeat(257),
+      }),
+    ).toMatchObject({ ok: false, code: 'INVALID_TOOL' });
+  });
+
   test('observer revocation and monotonic TTL expiry deny the next mutator', async () => {
     const { socket } = await startBroker();
     const sessionId = await register(socket);
@@ -400,9 +446,7 @@ raise SystemExit(0 if len(session_id) == 64 and hook_present and denied else 1)
       const adapter = {
         harnessPreflight: () => {},
         composePrompt: () => '# composed Claude contract',
-        // Pre-remediation Claudex uses this direct boundary and therefore bypasses registration.
-        exec: run,
-        // The remediated orchestration must select this shared register-before-exec boundary.
+        // Claudex exposes only the shared register-before-exec boundary.
         execLeaseGated: (args: string[], env: NodeJS.ProcessEnv) =>
           run('python3', [launcherPath, '--runtime', 'claude', '--', 'claude', ...args], env),
       } as unknown as ClaudexHarnessAdapter;
@@ -438,8 +482,8 @@ raise SystemExit(0 if len(session_id) == 64 and hook_present and denied else 1)
       });
 
       expect(execution).toBeDefined();
-      expect(execution!.status, execution!.stderr).toBe(0);
-      expect(JSON.parse(execution!.stdout)).toEqual({
+      expect(execution!.status, String(execution!.stderr)).toBe(0);
+      expect(JSON.parse(String(execution!.stdout))).toEqual({
         session_id: expect.stringMatching(/^[a-f0-9]{64}$/),
         hook_present: true,
         denied: true,