fix: MCP window shows 'Not connected' while the stdio bridge is serving requests - #1349
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Scriptwonder merged 2 commits intoAug 31, 2026
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After a domain reload, StdioBridgeHost resumes its TCP listener through an editor-idle retry loop once the OS releases the port. That path bypasses TransportManager.StartAsync, so the manager's cached TransportState stays Disconnected while the bridge is actually serving requests. The MCP for Unity window reads that cached snapshot, so it reports 'Not connected' indefinitely (until a manual Verify), which is especially misleading during compile-heavy sessions where reloads are frequent. Fix in two layers: - StdioTransportClient.State now refreshes its snapshot from StdioBridgeHost.IsRunning whenever the two disagree, in both directions (late bind after a busy port, or a listener that died without StopAsync). - TransportManager.GetState(Stdio) reconciles its own cached state with the client's live connectivity before returning it, creating the client lazily so host auto-start (CI, [InitializeOnLoad]) is also covered. Adds EditMode tests pinning both reconcile directions.
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No actionable comments were generated in the recent review. 🎉 ℹ️ Recent review info⚙️ Run configurationConfiguration used: defaults Review profile: CHILL Plan: Pro Plus Run ID: 📒 Files selected for processing (3)
Included review availability: Your plan provides up to 10 included reviews per hour; 8 remain after this review. 📝 WalkthroughWalkthroughThe stdio client and transport manager now reconcile cached transport state with live bridge connectivity and port changes. EditMode tests cover bridge startup, shutdown, and port changes that occur outside manager-controlled operations. ChangesStdio state reconciliation
Estimated code review effort: 3 (Moderate) | ~20 minutes Merge Risk: 🔵 Low · up to The change fixes false “Not connected” status while the stdio bridge is serving requests. It is mergeable with owner awareness that a concurrent stop or port rebind could briefly make the displayed running state and port inconsistent. Suggested reviewers: 🚥 Pre-merge checks | ✅ 4 | ❌ 1❌ Failed checks (1 warning)
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Inline comments:
In `@MCPForUnity/Editor/Services/Transport/Transports/StdioTransportClient.cs`:
- Around line 25-31: Refresh stdio state when the live bridge port changes, not
only when connectivity changes. In StdioTransportClient.cs lines 25-31, compare
StdioBridgeHost.GetCurrentPort() with _state.Port while running and replace
_state when either connectivity or port differs; in TransportManager.cs lines
153-159, reconcile _stdioState from client.State when the connected port differs
as well.
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MCPForUnity/Editor/Services/Transport/TransportManager.csMCPForUnity/Editor/Services/Transport/Transports/StdioTransportClient.csTestProjects/UnityMCPTests/Assets/Tests/EditMode/Services/TransportManagerTests.cs
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A stop/start cycle between two state reads can rebind the listener to a different port (the 6400<->6401 busy-port fallback) while both cached snapshots stay 'connected', leaving a stale port in the window. Compare the live bound port as well as connectivity when deciding to refresh, in both StdioTransportClient.State and TransportManager's reconcile. Addresses CodeRabbit review on CoplayDev#1349; adds an EditMode test pinning the rebind case and docstrings on the new tests.
A stop/start cycle between two state reads can rebind the listener to a different port (the 6400<->6401 busy-port fallback) while both cached snapshots stay 'connected', leaving a stale port in the window. Compare the live bound port as well as connectivity when deciding to refresh, in both StdioTransportClient.State and TransportManager's reconcile. Addresses CodeRabbit review on CoplayDev#1349; adds an EditMode test pinning the rebind case and docstrings on the new tests.
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Thanks for the PR! This is a long-lasting issue and I am glad to see this. Will merge and try it out myself, thanks! |
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Description
After a domain reload,
StdioBridgeHostresumes its TCP listener through its editor-idle retry loop once the OS releases the port (the busy-port path from #1173). That resume path — and CI/[InitializeOnLoad]auto-start — bypassesTransportManager.StartAsync, so the manager's cachedTransportStatestaysDisconnectedwhile the bridge is actually up and serving tool calls.The MCP for Unity window reads that cached snapshot (
BridgeControlService.IsRunning→TransportManager.GetState), so it reports Not connected indefinitely until a manual Verify. During compile-heavy sessions (frequent reloads + port ping-pong between 6400/6401) the window is wrong most of the time, sending users chasing a connection problem that doesn't exist.Reproduced on macOS, Unity 6000.3.15f1, package v10.1.0: window showed Not connected while MCP tool calls (including
execute_code) succeeded;TransportManager.IsRunning(Stdio)returnedfalsewith the listener bound and a handshake ping succeeding on the same port.Type of Change
Changes Made
Two-layer reconcile, no behavior change on the HTTP path:
StdioTransportClient.Staterefreshes its snapshot from the live listener whenever connectivity or the bound port disagrees — covering the late bind after a busy port, a listener that died withoutStopAsync, and a stop/start cycle that rebinds to a different port between two reads.TransportManager.GetState(Stdio)reconciles its own cached state with the client's live connectivity and port before returning it, creating the client lazily so host auto-start without any priorStartAsyncis also covered.TransportManagerTestspin all three reconcile directions (start outside manager, stop outside manager, port rebind while connected) using a fake stdio client whose connectivity/port flip without going through Start/Stop.Compatibility / Package Source
file:(local clone of this repo, branchfix/stdio-window-state-desyncoffbeta)Packages/packages-lock.json: n/a (file reference)Testing/Screenshots/Recordings
Full EditMode suite on 2022.3.62f1 (direct
-runTests -testResultsinvocation): 1113 passed, 0 failed (66 pre-existing ignores), new tests passing.Documentation Updates
Related Issues
Relates to #1173 (the busy-port fallback whose resume path bypasses the manager state).
Additional Notes
tools/check-unity-versions.sh --fullcurrently passes-quittogether with-runTests, which makes Unity exit after import without executing any tests (its log shows no test run; exit code is 0 regardless). I verified with a direct-runTests -testResultsinvocation instead — happy to file that separately.Summary by CodeRabbit