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workaround: avoid SDK cancellation serialization bug#320
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Pass CancellationToken.None to SDK SendAsync calls to prevent StreamJsonRpc's StandardCancellationStrategy from attempting to serialize RequestId, which is not included in the SDK's AOT-safe JSON context. ## Root Cause (SDK Bug) When a CancellationToken fires during an SDK call: 1. StreamJsonRpc's StandardCancellationStrategy.CancelOutboundRequest() tries to send a \$/cancelRequest notification 2. This requires serializing StreamJsonRpc.RequestId 3. The SDK's SystemTextJsonFormatter doesn't include RequestId in its TypeInfoResolverChain (ClientJsonContext, TypesJsonContext, etc.) 4. NotSupportedException is thrown, becomes unobserved, kills the JSON-RPC reader loop silently 5. Session gets stuck — no events arrive, watchdog eventually fires ## Why This Workaround Works PolyPilot already handles cancellation at the TCS level: - AbortSessionAsync calls ResponseCompletion.TrySetCanceled() - Watchdog timeout clears IsProcessing state - All abort/error paths properly clean up state The CancellationToken was only used by SDK to send server-side cancellation notifications — which is the broken path. ## Trade-off The server won't receive \$/cancelRequest notifications, so it may continue processing cancelled requests. However: - Local state is correctly cleaned up (good UX) - Watchdog provides safety net - Server resources are wasted but operations complete gracefully ## Investigation 4 sub-agents analyzed: SDK changelogs (no breaking changes), SDK Client.cs (confirms missing RequestId), PolyPilot usage (correct), SDK samples (don't use CancellationToken). All confirmed SDK bug. Fixes #319 Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
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- CRITICAL: Fix missed call site in PolyPilot.Console/Models/AgentSession.cs The Console app was also vulnerable to the RequestId serialization crash. - MODERATE: Add comment about watchdog limitation when SendAsync blocks If the transport write itself blocks (half-open TCP), watchdog completes the TCS but execution never reaches it. Edge-case on mobile/codespace. - MINOR: Add explanatory comment to soft-steer path (line 2702) Functionally safe (implicit CancellationToken.None) but prevents future maintainers from accidentally reintroducing the bug. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
…tion If SendAsync throws (transport error, connection dropped, etc.), execution exits without resetting IsProcessing. Unlike CopilotService, AgentSession has no watchdog — only event handlers reset the flag. If SendAsync throws before sending, no events arrive, and IsProcessing stays true forever → all subsequent calls throw 'already processing'. Fix: Wrap SendAsync and TCS await in try/catch that resets IsProcessing on any exception before re-throwing. Note: The TrySetCanceled() path self-heals because the server continues processing (CancellationToken.None) and eventually fires SessionIdleEvent. The SendAsync exception path does not self-heal without this fix. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
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## Summary Pass \CancellationToken.None\ to SDK \SendAsync\ calls to prevent \StreamJsonRpc\'s \StandardCancellationStrategy\ from attempting to serialize \RequestId\, which is not included in the SDK's AOT-safe JSON context. Fixes PureWeen#319 ## Root Cause (SDK Bug) When a \CancellationToken\ fires during an SDK call: 1. \StreamJsonRpc.StandardCancellationStrategy.CancelOutboundRequest()\ tries to send a \$/cancelRequest\ notification 2. This requires serializing \StreamJsonRpc.RequestId\ 3. The SDK's \SystemTextJsonFormatter\ doesn't include \RequestId\ in its \TypeInfoResolverChain\ 4. \NotSupportedException\ is thrown, becomes unobserved, kills the JSON-RPC reader loop silently 5. Session gets stuck — no events arrive, watchdog eventually fires ## Why This Workaround Works PolyPilot already handles cancellation at the TCS level: - \AbortSessionAsync\ calls \ResponseCompletion.TrySetCanceled()\ - Watchdog timeout clears \IsProcessing\ state - All abort/error paths properly clean up state The \CancellationToken\ was only used by SDK to send server-side cancellation notifications — which is the broken path. ## Trade-off The server won't receive \$/cancelRequest\ notifications, so it may continue processing cancelled requests. However: - Local state is correctly cleaned up (good UX) - Watchdog provides safety net - Server resources are wasted but operations complete gracefully ## Investigation Summary 4 parallel sub-agents analyzed: | Agent | Focus | Finding | |-------|-------|---------| | SDK changelogs | Breaking changes | None documented for cancellation | | SDK Client.cs | JsonRpc config | Confirms \StandardCancellationStrategy\ used, \RequestId\ missing from JSON context | | PolyPilot audit | CancellationToken usage | Our usage is correct | | SDK samples | Recommended patterns | Don't use CancellationToken at all | **All agents agree**: This is an SDK bug, not a PolyPilot defect. ## Changes - **CopilotService.cs**: 2 lines changed - Primary \SendAsync\ call (line 2351) - Reconnect retry \SendAsync\ call (line 2499) ## Testing - Build passes - 139 watchdog tests pass - Manual testing: orchestrator sessions no longer get stuck on cancellation ## SDK Versions Affected - Broken: 0.1.30+ (after AOT/trimming changes) - Works: 0.1.26 Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com> --------- Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
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Summary
Pass \CancellationToken.None\ to SDK \SendAsync\ calls to prevent \StreamJsonRpc's \StandardCancellationStrategy\ from attempting to serialize \RequestId, which is not included in the SDK's AOT-safe JSON context.
Fixes #319
Root Cause (SDK Bug)
When a \CancellationToken\ fires during an SDK call:
Why This Workaround Works
PolyPilot already handles cancellation at the TCS level:
The \CancellationToken\ was only used by SDK to send server-side cancellation notifications — which is the broken path.
Trade-off
The server won't receive $/cancelRequest\ notifications, so it may continue processing cancelled requests. However:
Investigation Summary
4 parallel sub-agents analyzed:
All agents agree: This is an SDK bug, not a PolyPilot defect.
Changes
Testing
SDK Versions Affected
Co-authored-by: Copilot 223556219+Copilot@users.noreply.github.com