[Chore] Unskip VS Code e2e replay for subtasks

[roomote]

Opened on behalf of Elliott de Launay. View the task or mention @roomote for follow-up asks.

What problem this solves

Fixes an issue where the subtasks VS Code e2e replay still missed the cancelled-child resume path, which left delegated cancellation behavior under-covered and could let a cancelled child reopen its parent when it later finished.

Why this change was made

This keeps the test on the same cancelled child, validates the actual follow-up tool results in replay mode, teaches mock mode how the resumed child re-asks the follow-up, and detaches a user-cancelled delegated child from the parent it was previously blocking before that child is rehydrated.

AttemptCompletionTool mirrors that detach with an idempotency guard so a cancelled-then-resumed child whose parent is no longer awaiting it falls through to the normal completion-ask flow instead of delegating back into the parent.

User impact

No direct UI change. The subtasks replay suite now catches delegated cancellation regressions, and a cancelled delegated child can finish without reviving the parent task it was cancelled out of.

Related PRs

• Read-only tools
• Mutating tools
• use_mcp_tool

[roomote]

No actionable issues found. See task

• apps/vscode-e2e/src/suite/subtasks.test.ts is unskipped again on the current head.
• The spawned-child wait now follows the active task from the end of api.getCurrentTaskStack(), so the replay reaches the delegated cancellation path instead of timing out on the parent task.
• apps/vscode-e2e/src/suite/subtasks.test.ts: the cancellation probe now stays on the same cancelled child instead of starting anotherTaskId, so the test still exercises the parent-awaiting-child state after cancellation.
• apps/vscode-e2e/src/fixtures/subtasks.ts: the follow-up fixtures now validate the actual tool result payload and cover the resumed-child replay path before completing with 9.
• apps/vscode-e2e/src/suite/subtasks.test.ts: the resumed child now asserts clean completion with 9, no emitted error message, and a task stack that still ends on that cancelled child.
• src/core/webview/ClineProvider.ts: clearing runtime parent references on the rehydrated cancelled child no longer detaches its persisted lineage, so resumed cancelled subtasks keep their back-to-parent affordance and history grouping.
• codecov/patch is passing on the current head.
• platform-unit-test (ubuntu-latest) passed on the current head.
• platform-unit-test (windows-latest) passed on the current head.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

📢 Thoughts on this report? Let us know!

[roomote]

I see some merge conflicts here. Working on them now...

[roomote]

I see some merge conflicts here. Working on them now...

[roomote]

I see some merge conflicts here. Working on them now...

[roomote]

I see some merge conflicts here. Working on them now...

[roomote]

I see some merge conflicts here. Working on them now...

[roomote]

Addressed the three open review threads and pushed the follow-up in d5d5ae3.

The shipped diff now keeps the subtasks probe on the same cancelled child task, captures that resumed child's final completion_result and error messages, and asserts the task stack still ends on the cancelled child instead of spinning up a fresh anotherTaskId. subtasks.ts now validates the actual follow-up answer with toolResultContains(...) and adds a resumed-child replay fixture so mock mode only completes after the resumed follow-up path really answers with 9. ClineProvider.cancelTask() also clears the delegation link before rehydrating a user-cancelled delegated child, with focused unit coverage in ClineProvider.flicker-free-cancel.spec.ts, so finishing that cancelled child no longer reopens the parent it was cancelled from.

Validation on the pushed head is clean: TEST_FILE=subtasks.test pnpm --dir apps/vscode-e2e test:ci:mock, pnpm --dir src test core/webview/__tests__/ClineProvider.flicker-free-cancel.spec.ts, pnpm --dir apps/web-roo-code test, and http://127.0.0.1:3000 all passed. Browser proof was not applicable because this is delegated-task lifecycle and e2e replay coverage work, not a rendered UI change.