Actions Debugger [Public Preview]

### Value Prop
The Actions Debugger gives developers an interactive way to troubleshoot GitHub Actions workflows in real time, so you can spend less time guessing and more time building. Securely attach to a running job during execution, inspect environment variables, filesystem state, and step outputs with a debug client of your choice, and re-run individual steps without restarting the entire workflow.

### Expected Outcome
By making debugging interactive and efficient, we aim to shorten feedback cycles and reduce the guesswork involved in fixing workflow problems. Developers will be able to quickly validate assumptions, understand failures, and resolve issues, leading to smoother CI/CD workflows and a better overall experience with GitHub Actions.

The issue provides only a value proposition and expected outcome for an Actions Debugger; it names no files, tests, or entry points. First confirm the implementation repository and scope with maintainers, then define how secure attachment, inspection, and step re-runs will be validated.

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