fix: Handle ObjectDisposedException when disposing linked CancellationTokenSource

[thomhurst]

Summary

• Fixes race condition where CancelAfter is called on an already-disposed linked CancellationTokenSource
• The linked CTS can be disposed when the parent engine token is cancelled before DisposeAsync is called
• Wraps the CancelAfter call in a try-catch to gracefully handle this case

Context

This bug was exposed by the logging improvements in PR #1711. The error manifests as:

System.ObjectDisposedException: The CancellationTokenSource has been disposed.
   at System.Threading.CancellationTokenSource.ThrowObjectDisposedException()
   at System.Threading.CancellationTokenSource.CancelAfter(Int32 millisecondsDelay)
   at ModularPipelines.Engine.Executors.PrintProgressExecutor.DisposeAsync() in PrintProgressExecutor.cs:line 49

Test plan

• Build succeeds
• CI pipeline passes
• No ObjectDisposedException in logs

🤖 Generated with Claude Code

[thomhurst]

Summary

Fixes a race condition where CancelAfter is called on an already-disposed linked CancellationTokenSource in the progress executor.

Critical Issues

None found ✅

Suggestions

The fix looks good and follows existing patterns in the codebase (see src/ModularPipelines/Context/Command.cs:282 for a similar pattern). The addition of the explanatory comment is actually an improvement over the existing pattern.

One minor observation: The comment could be slightly more precise. Consider:

// The linked CancellationTokenSource may already be disposed if the parent engine token was cancelled

vs. the current:

// Linked CancellationTokenSource may already be disposed if the engine token was cancelled

Both are fine - just a matter of consistency with the rest of the codebase.

Verdict

✅ APPROVE - No critical issues

The fix correctly handles the race condition between the parent token cancellation (which disposes the linked token source) and the explicit disposal in DisposeAsync. This is a legitimate defensive coding pattern for async disposal scenarios.

[Copilot]

Pull request overview

This PR fixes a race condition in PrintProgressExecutor where calling CancelAfter on an already-disposed linked CancellationTokenSource throws ObjectDisposedException. The race occurs when the parent engine token is cancelled before DisposeAsync is invoked, causing the linked CTS to be disposed.

Key changes:

• Added try-catch block around CancelAfter call to handle ObjectDisposedException
• Added explanatory comment describing when this race condition occurs