feat(worfklow): added cancellation after launching manual execution

[waleedlatif1]

Description

Added the ability to cancel a run once its been launched. This prevents users with longer workflows from having to wait until the entire run is complete. Speeds up iteration.

Type of change

• New feature (non-breaking change which adds functionality)

How Has This Been Tested?

Tested manually

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have added tests that prove my fix is effective or that my feature works
• All tests pass locally and in CI (bun run test)
• My changes generate no new warnings
• Any dependent changes have been merged and published in downstream modules
• I have updated version numbers as needed (if needed)
• I confirm that I have read and agree to the terms outlined in the Contributor License Agreement (CLA)

Security Considerations:

• My changes do not introduce any new security vulnerabilities
• I have considered the security implications of my changes

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[greptile-apps]

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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