test: add comprehensive test cases for streaming cancellation

[roomote]

Summary

This PR adds comprehensive test cases for the streaming cancellation mechanism, as requested by @pwilkin in issue #7014.

Changes

• Added new test file with 4 comprehensive test cases:
  1. Test for cancelling endless streaming responses - Verifies that an infinite stream can be properly cancelled when the abort flag is set
  2. Test for cancellation during chunk processing - Ensures cancellation works correctly even when chunks are actively being processed
  3. Test for immediate abort flag setting - Validates that setting the abort flag immediately prevents any chunks from being processed
  4. Test for proper resource cleanup - Confirms that all resources are properly cleaned up during cancellation

Testing

All tests pass successfully:

• The tests simulate endless streaming responses using async generators
• They verify that the abort mechanism works correctly in all scenarios
• They ensure proper cleanup of resources when cancellation occurs

Related Issues

• Addresses feedback in Cancel does not cancel streaming #7014
• Tests the fix implemented in PR fix: ensure cancel button properly aborts streaming responses (#7014) #7016

Notes

These tests provide confidence that the cancellation mechanism is robust and handles edge cases properly, including the scenario where chunks are arriving constantly and the abort flag needs to interrupt the stream immediately.

cc @pwilkin

---

Important

Adds comprehensive test cases for streaming cancellation in Task.cancellation.spec.ts, covering endless streaming, chunk processing, immediate abort, and resource cleanup.

• Tests Added:
  • Task.cancellation.spec.ts includes 4 new test cases for streaming cancellation.
  • Tests cover endless streaming cancellation, chunk processing cancellation, immediate abort, and resource cleanup.
• Behavior:
  • Verifies cancellation of infinite streams when abort flag is set.
  • Ensures cancellation during active chunk processing.
  • Validates immediate abort flag prevents chunk processing.
  • Confirms proper resource cleanup during cancellation.
• Mocks and Setup:
  • Mocks for vscode, fs/promises, delay, and other modules to simulate environment.
  • Uses async generators to simulate streaming responses.

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[roomote]

I wrote tests to test my own code. The recursion is strong with this one.

[roomote]

Is this intentional? The tests directly manipulate task.abort = true rather than using the public abortTask() method. The actual implementation in Task.ts shows that abortTask() does more than just setting the flag - it calls dispose(), saves messages, etc. Consider testing through the public API for better test isolation:

Suggested change

	task.abort = true
	await task.abortTask()

[roomote]

Could we avoid potential double-setting of iteratorReturnCalled? Both the finally block (line 265) and the return() method (line 269) set this flag. Consider using just one approach for clarity.

[roomote]

These console.log statements might clutter test output. Consider removing them or converting to test assertions if the information is important for debugging:

Suggested change

	console.log("Stream aborted at iteration", streamIterations)
	// Stream aborted at iteration

[roomote]

Consider extracting these magic numbers to named constants for better maintainability:

Suggested change

	await new Promise((resolve) => setTimeout(resolve, 50))
	const NETWORK_DELAY_MS = 5;
	const SHORT_WAIT_MS = 20;
	const MEDIUM_WAIT_MS = 30;
	const LONG_WAIT_MS = 50;
	const MAX_ITERATIONS = 100;

Then use them throughout the tests for consistency.