test(#838): bound adapter failure proof

docs/scratchpads/838-broker-acceptance-flake.md

@@ -40,3 +40,5 @@ Eliminate high-contention uncaught JSON parse failures in lease-broker and mutat
 - Review RED evidence: delayed cross-chunk garbage resolved `{ ok: true }` instead of rejecting, and a truncated `promotion_token` remained in the typed error. The tests use separate timed writes to prevent kernel/event-loop coalescing.
 - Review remediation: the shared client now accumulates through EOF, requires exactly one terminal newline, then parses inside a rejecting error boundary. Diagnostic bodies are capped at 256 bytes, sensitive broker fields are fully redacted, and a SHA-256 digest preserves correlation without credential disclosure.
 - Post-review coverage: `broker-test-client.ts` 99.35% statements/lines, 86.66% branches, 100% functions. Final full suite is 73 files / 1,394 tests plus all Python/shell gates; recursive build, typecheck, lint, and format are green.
+- Fresh exact-head Codex security review: risk `none`, no findings. Fresh code review found only that the real-adapter subprocess proof lacked a timeout; it now has a five-second bound and fails with runtime/wire context while closing the fake server. The focused Python suite remains 15/15 green.
+- Mandatory Opus SECREV remains coordinator-owned and pending before any push/PR decision; this build is intentionally local-only.

packages/mosaic/src/mutator-gate/runtime_tools_unittest.py

@@ -254,13 +254,21 @@ class ExecutableEntrypointTest(unittest.TestCase):
                         "MOSAIC_LEASE_SESSION_ID": "d" * 64,
                         "MOSAIC_RUNTIME_GENERATION": "1",
                     }
-                    result = subprocess.run(
-                        [sys.executable, str(TOOLS_DIR / "mutator-gate.py"), "--runtime", runtime],
-                        input=b'{"tool_name":"Read"}\n',
-                        capture_output=True,
-                        env=environment,
-                        check=False,
-                    )
+                    try:
+                        result = subprocess.run(
+                            [sys.executable, str(TOOLS_DIR / "mutator-gate.py"), "--runtime", runtime],
+                            input=b'{"tool_name":"Read"}\n',
+                            capture_output=True,
+                            env=environment,
+                            check=False,
+                            timeout=5,
+                        )
+                    except subprocess.TimeoutExpired as exc:
+                        server.close()
+                        thread.join(timeout=2)
+                        self.fail(
+                            f"{runtime} gate hung on wire reply {wire_reply!r}: {exc}"
+                        )
                     thread.join(timeout=2)
 
                     self.assertFalse(thread.is_alive())