Greptile Summary

This PR implements workflow execution cancellation functionality across the entire execution stack. The changes add the ability for users to cancel running workflows through a UI button, which integrates with a new cancellation mechanism in the core executor.

The implementation follows a clean architecture pattern:

1. Core Executor Changes: The Executor class now includes a private isCancelled boolean flag and a public cancel() method. The execution loop checks this flag at key points (while loop condition and continueExecution method) to halt processing when cancellation is requested. When cancelled, the executor returns a structured error response with telemetry tracking.

2. Hook Integration: The useWorkflowExecution hook adds a handleCancelExecution callback that calls the executor's cancel method and properly resets all execution state (including debug state cleanup). It also detects cancellation in streaming executions by checking for the specific error message.

3. UI Enhancement: The control bar component conditionally renders a red cancel button with an X icon when isExecuting is true, replacing the normal run button. This provides immediate visual feedback and user control.

4. Test Coverage: Comprehensive test suite covers all cancellation scenarios including basic flag setting, debug mode cancellation, multiple cancel calls, prevention of new execution on cancelled executors, and cancellation during execution loops.

The feature integrates seamlessly with existing execution patterns, supporting both normal and debug mode workflows while maintaining proper state management and telemetry tracking.

Confidence score: 4/5

• This PR is generally safe to merge with well-structured cancellation implementation and comprehensive test coverage
• Score reflects solid implementation but minor concerns about potential race conditions in streaming execution and state cleanup timing
• Files needing attention: use-workflow-execution.ts for streaming cancellation logic and potential executor cleanup timing

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