[codex] Fix stale AIO sandbox cache reuse (#3494)

* Fix stale AIO sandbox cache reuse

* Address AIO sandbox review feedback

* Distinguish sandbox health check failures

* Keep local discovery recoverable when the runtime check fails

LocalContainerBackend.discover() shares _is_container_running, which now
raises on transient daemon errors instead of returning False. Discovery has
no exception handling in _discover_or_create_with_lock(_async), so a brief
Docker hiccup turned a recoverable "could not verify, create instead" into a
hard acquire failure. Catch the check failure inside discover() and return
None so an unverifiable container is simply not adopted, restoring the
pre-change fall-through while keeping raise-on-unknown semantics protecting
the destroy path.

Reported by fancy-agent on PR #3494.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

* Narrow the not-found match in container inspect error handling

A bare "not found" substring also matches transient failures like "command
not found" or "context not found", which would misclassify a check error as
"container definitely gone" and bypass the raise-on-unknown contract. Keep
Docker's specific "No such object"/"No such container" phrases, and only
trust a generic "not found" (Apple Container) when the message names the
inspected container or refers to a container/object.

Reported by WillemJiang on PR #3494.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

---------

Co-authored-by: Claude Fable 5 <noreply@anthropic.com>

backend/tests/test_remote_sandbox_backend.py

@@ -257,14 +257,38 @@ def test_provisioner_is_alive_true_only_when_status_running(monkeypatch):
     assert backend._provisioner_is_alive("abc123") is False
 
 
-def test_provisioner_is_alive_returns_false_on_request_exception(monkeypatch):
+def test_provisioner_is_alive_returns_false_on_404(monkeypatch):
+    backend = RemoteSandboxBackend("http://provisioner:8002")
+
+    def mock_get(url: str, timeout: int):
+        return _StubResponse(status_code=404)
+
+    monkeypatch.setattr(requests, "get", mock_get)
+    assert backend._provisioner_is_alive("abc123") is False
+
+
+def test_provisioner_is_alive_raises_on_request_exception(monkeypatch):
     backend = RemoteSandboxBackend("http://provisioner:8002")
 
     def mock_get(url: str, timeout: int):
         raise requests.RequestException("boom")
 
     monkeypatch.setattr(requests, "get", mock_get)
-    assert backend._provisioner_is_alive("abc123") is False
+    with pytest.raises(RuntimeError, match="Provisioner health check failed for abc123"):
+        backend._provisioner_is_alive("abc123")
+
+
+def test_provisioner_is_alive_raises_on_server_error(monkeypatch):
+    backend = RemoteSandboxBackend("http://provisioner:8002")
+
+    def mock_get(url: str, timeout: int):
+        response = _StubResponse(status_code=503)
+        response.text = "unavailable"
+        return response
+
+    monkeypatch.setattr(requests, "get", mock_get)
+    with pytest.raises(RuntimeError, match="HTTP 503 unavailable"):
+        backend._provisioner_is_alive("abc123")
 
 
 def test_discover_delegates_to_provisioner_discover(monkeypatch):