Metadata‑driven subtasks (no UI changes): automatic parent resume and single‑open safety

[hannesrudolph]

Closes: #8081

Summary

This update makes subtask hand‑offs smoother while keeping the UI exactly the same:

• Subtasks now maintain their connection from child to parent even when VS Code has been restarted
• Automatic parent resume: when a subtask finishes, the parent continues without a “resume task” prompt.
• Single‑open safety: only one task is open at a time to avoid race conditions and state conflicts.

What you’ll notice

• Fewer interruptions and faster hand‑offs between tasks.
• No visual changes in this PR; all improvements are behavioral.

---

Important

Introduce metadata-driven subtasks with automatic parent resume and single-open safety, adding delegation events and updating task handling logic.

• Behavior:
  • Introduces metadata-driven subtasks with automatic parent resume and single-open safety.
  • Adds delegation events: TaskDelegated, TaskDelegationCompleted, TaskDelegationResumed in ExtensionChannel.ts and api.ts.
  • Removes finishSubTask method in ClineProvider.ts and replaces it with metadata-driven delegation logic.
• Tests:
  • Adds tests for delegation events in ExtensionChannel.test.ts and new test files like delegation-events.spec.ts.
  • Tests for single-open-task invariant in single-open-invariant.spec.ts.
• Misc:
  • Updates Task class in Task.ts to support new delegation flow.
  • Minor changes in webviewMessageHandler.ts to handle task clearing with new logic.

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[roomote]

Rooviewer   See task on Roo Cloud

All previously flagged issues have been resolved. No new issues found.

• skipPrevResponseIdOnce property is declared and set but never consumed in the codebase, making it non-functional

Previous reviews

• 68281ef: Review #1
• b47a930: Review #2
• 1977ea5: Review #3
• ced7628: Review #4
• e9efe90: Review #5
• 55a953f: Review #6
• 05e6a98: Review #7

_{Mention @roomote in a comment to request specific changes to this pull request or fix all unresolved issues.}

[roomote]

Skipping the entire test suite defeats the purpose of having tests for critical abort noise prevention logic. If these tests are no longer relevant due to the refactor, they should be updated to reflect the new implementation rather than disabled. This leaves the checkpoint abort handling untested and could allow regressions in error handling during task disposal.

_{Fix it with Roo Code or mention @roomote and request a fix.}