fix: make removeClineFromStack() delegation-aware to prevent orphaned parent tasks

[roomote]

Related GitHub Issue

Closes: #11301

Description

This PR attempts to address Issue #11301 where parent tasks become orphaned in a delegated state when a child task is removed via removeClineFromStack().

Root cause: removeClineFromStack() is a pure pop-and-dispose operation with no delegation awareness. When a delegated child task is removed (via Clear Task, navigate to history, or start new task), the parent's HistoryItem remains stuck with status: "delegated" and a stale awaitingChildId.

Fix: Makes removeClineFromStack() the delegation-aware chokepoint. After popping and disposing the child task, it now:

1. Captures parentTaskId and childTaskId before abort/dispose (since abortTask(true) is async and the task reference is cleared later)
2. Looks up the parent's HistoryItem via getTaskWithId(parentTaskId)
3. If the parent has status === "delegated" and awaitingChildId === childTaskId, updates parent metadata: status -> "active", awaitingChildId -> undefined
4. Persists via updateTaskHistory()
5. Wraps the parent lookup + update in try/catch so failures are non-fatal (logged but do not block the pop)

This is a lightweight metadata repair (~20 lines), not a full delegation return. The parent simply becomes resumable from the task history list. All three affected paths (and any future callers) go through removeClineFromStack(), so this single fix covers everything.

Test Procedure

• Added 6 new tests in src/__tests__/removeClineFromStack-delegation.spec.ts:
  • Delegated child removal repairs parent metadata (delegated -> active, awaitingChildId cleared)
  • Non-delegated task removal does not trigger any parent metadata changes
  • Mismatched awaitingChildId does not trigger repair
  • Non-delegated parent status does not trigger repair
  • Errors during parent lookup are caught and logged without blocking the pop
  • Empty stack is handled gracefully
• All existing delegation-related tests continue to pass (provider-delegation.spec.ts, history-resume-delegation.spec.ts, nested-delegation-resume.spec.ts, single-open-invariant.spec.ts)
• ClineProvider.spec.ts (88 tests) continues to pass

Pre-Submission Checklist

• Issue Linked: This PR is linked to an approved GitHub Issue (see "Related GitHub Issue" above).
• Scope: My changes are focused on the linked issue (one major feature/fix per PR).
• Self-Review: I have performed a thorough self-review of my code.
• Testing: New and/or updated tests have been added to cover my changes (if applicable).
• Documentation Impact: No documentation updates required.
• Contribution Guidelines: I have read and agree to the Contributor Guidelines.

Documentation Updates

• No documentation updates are required.

Additional Notes

Feedback and guidance are welcome.

---

Important

Enhance removeClineFromStack() in ClineProvider.ts to update parent task metadata when a delegated child is removed, preventing orphaned parent tasks.

• Behavior:
  • removeClineFromStack() in ClineProvider.ts now updates parent task metadata when a delegated child is removed, changing status from delegated to active and clearing awaitingChildId.
  • Handles errors during parent metadata update without blocking task removal.
  • Skips metadata repair if skipDelegationRepair option is true.
• Tests:
  • Added removeClineFromStack-delegation.spec.ts with tests for parent metadata repair, non-delegated task removal, mismatched awaitingChildId, non-delegated parent status, error handling, empty stack, and nested delegation transitions.
  • Ensures existing tests in provider-delegation.spec.ts, history-resume-delegation.spec.ts, and others continue to pass.

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[roomote]

Rooviewer   See task

Re-reviewed the incremental changes (45d756e). The previously flagged nested delegation issue is resolved via the skipDelegationRepair opt-out flag. The new Gemini empty-stream handling, reasoning effort validation, and recursive subtask tree UI changes are clean and well-tested. No new issues found.

• Fix: parent metadata repair in removeClineFromStack() incorrectly fires during delegateParentAndOpenChild() in nested delegation (3+ levels), prematurely resetting the grandparent's delegated status to active

Previous reviews

• 241c0a2: Review #1
• c085069: Review #2

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