Fix InProcessTestHost ContinueAsNew stuck-instance race condition

[bachuv]

Summary

What changed?

This pull request focuses on improving concurrency safety and correctness in the in-process test host, particularly around work item tracking and message handling during orchestration restarts. The most important changes are grouped below.

Concurrency Safety Improvements:

• Replaced direct access to the currentWorkItems field with thread-safe operations using Interlocked.Increment, Interlocked.Decrement, and Volatile.Read in WorkItemDispatcher.cs, ensuring accurate and race-free tracking of concurrent work items.

Orchestration Restart and Message Handling Fixes:

• In TaskOrchestrationDispatcher.cs, added logic to clear accumulated activity, timer, and orchestrator messages when a ContinueAsNew occurs, preventing stale messages from being re-enqueued and causing duplicate or stuck orchestrations.
• In InMemoryOrchestrationService.cs, added logic to drop messages from previous executions after a restart, preventing stale activity completions or timer fires from interfering with new orchestration runs.

Version Update:

• Bumped the package version in InProcessTestHost.csproj from 0.2.2-preview.1 to 0.2.3-preview.1 to reflect these changes.

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Project checklist

• Release notes are not required for the next release
  • Otherwise: Notes added to release_notes.md
• Backport is not required
  • Otherwise: Backport tracked by issue/PR #issue_or_pr
• All required tests have been added/updated (unit tests, E2E tests)
• Breaking change?
  • If yes:
    • Impact:
    • Migration guidance:

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AI-assisted code disclosure (required)

Was an AI tool used? (select one)

• No
• Yes, AI helped write parts of this PR (e.g., GitHub Copilot)
• Yes, an AI agent generated most of this PR

If AI was used:

• Tool(s): VS Code GitHub CoPilot (Claude Opus 4.6)
• AI-assisted areas/files:
• What you changed after AI output:

AI verification (required if AI was used):

• I understand the code and can explain it
• I verified referenced APIs/types exist and are correct
• I reviewed edge cases/failure paths (timeouts, retries, cancellation, exceptions)
• I reviewed concurrency/async behavior
• I checked for unintended breaking or behavior changes

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Testing

Automated tests

• Result: Passed
• 19/19 InProcessTestHost tests pass (15 existing + 4 new)
• New tests in ContinueAsNewRaceConditionTests:
  • ConcurrentContinueAsNew_MultipleIterations_NoneGetStuck — 6 concurrent instances, 5 ContinueAsNew iterations each with activity + 500ms timer
  • SingleInstance_ManyContinueAsNewIterations_CompletesCorrectly — 8 ContinueAsNew iterations with activity + timer per iteration
  • ContinueAsNew_MultipleActivitiesPerIteration_AllComplete — 4 concurrent instances with 3 parallel activities per iteration across 4 ContinueAsNew cycles
  • ReproScenario_RepeatedRounds_AllComplete — exact bug report scenario (4 instances, activity + 5s timer + ContinueAsNew) repeated across 3 fresh hosts

[Copilot]

Pull request overview

This PR improves correctness in the in-process sidecar used by Microsoft.DurableTask.InProcessTestHost, targeting a stuck-instance race condition triggered by ContinueAsNew under concurrency (especially when stale activity/timer messages from a prior execution interleave with a restarted execution).

Changes:

• Adds stress/regression tests that reproduce and validate the ContinueAsNew stuck-instance scenario under concurrency.
• Improves work-item concurrency tracking in the sidecar dispatcher using Interlocked and Volatile.
• Prevents stale message re-enqueue during ContinueAsNew by clearing accumulated message lists and dropping messages from prior executions.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
test/InProcessTestHost.Tests/ContinueAsNewTests.cs	Adds new regression/stress tests targeting the ContinueAsNew stale-message race.
src/InProcessTestHost/Sidecar/InMemoryOrchestrationService.cs	Drops messages for completed instances and attempts to drop messages from prior executions after restart.
src/InProcessTestHost/Sidecar/Dispatcher/WorkItemDispatcher.cs	Makes active work-item tracking thread-safe via Interlocked/Volatile.
src/InProcessTestHost/Sidecar/Dispatcher/TaskOrchestrationDispatcher.cs	Clears accumulated activity/timer/orchestrator message buffers when ContinueAsNew occurs.
src/InProcessTestHost/InProcessTestHost.csproj	Bumps package version to 0.2.3-preview.1.