fix(task-lifecycle): preserve parent-child link when delegated subtask is interrupted (#560)

[edelauna]

Related GitHub Issue

Closes: #560

Description

When a delegated subtask was cancelled mid-execution, cancelTask() immediately severed the parent–child link — parent transitioned from "delegated" → "active" with awaitingChildId cleared. When the user resumed the child and it called attempt_completion, the parent no longer awaited it, so it fell through to the standalone "Start New Task" flow instead of reporting back.

How it works

Before: cancel child → parent: delegated→active, awaitingChildId→undefined
        → child resumes → falls through to standalone "Start New Task"

After:  cancel child → child: active→interrupted, parent stays delegated
        → child resumes → delegates back to parent → parent completes

Changes

Core fix:

• packages/types/src/history.ts — Add "interrupted" to HistoryItem status enum
• packages/types/src/task.ts, src/core/task/Task.ts, src/core/task-persistence/taskMetadata.ts — Propagate "interrupted" through initialStatus types
• src/core/webview/ClineProvider.ts#cancelTask — Mark cancelled delegated child as "interrupted" instead of severing parent link; await abortTask() promise before writing "interrupted" to prevent a late saveClineMessages write from downgrading the status back to "active"
• src/core/webview/ClineProvider.ts#removeClineFromStack — Skip parent auto-repair when child history shows "interrupted" (parent must stay "delegated" for resume)
• src/core/tools/AttemptCompletionTool.ts — Accept "interrupted" alongside "active" so resumed children can delegate back to parent

CLI/session type sync:

• packages/core/src/task-history/index.ts — Add "interrupted" to session reader allow-list so persisted interrupted sessions are not silently dropped
• apps/cli/src/ui/types.ts, apps/cli/src/ui/components/autocomplete/triggers/HistoryTrigger.tsx — Add "interrupted" to status unions; display interrupted tasks with ⏸ icon and cyan color

Test Procedure

Unit tests (3 files updated, 3 new tests added):

• src/core/webview/__tests__/ClineProvider.flicker-free-cancel.spec.ts — Updated existing cancel tests; added tests asserting child is marked "interrupted" and parent stays "delegated"
• src/__tests__/removeClineFromStack-delegation.spec.ts — Added test asserting parent is not auto-repaired when child is "interrupted"
• src/core/tools/__tests__/attemptCompletionTool.spec.ts — Added test for interrupted child delegating back to parent
• apps/cli/src/ui/components/autocomplete/triggers/__tests__/HistoryTrigger.test.tsx — Added test asserting ⏸ icon renders for interrupted status

E2E test:

• apps/vscode-e2e/src/suite/subtasks.test.ts — New test: interrupt child mid-execution → resume → asserts child reports back to parent and parent completes with expected result

All unit tests pass: pnpm vitest run (408/408 files).

Pre-Submission Checklist

• Issue Linked: Closes fix(task-lifecycle): preserve parent-child link when delegated subtask is interrupted #560
• Scope: Focused on subtask interrupt/resume lifecycle
• Self-Review: Performed
• Testing: Unit tests updated/added + new E2E test added
• Documentation Impact: No documentation updates required
• Contribution Guidelines: Read and agreed

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[codecov]

Codecov Report

❌ Patch coverage is 88.00000% with 3 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
src/extension/api.ts	0.00%	2 Missing ⚠️
src/core/tools/AttemptCompletionTool.ts	0.00%	0 Missing and 1 partial ⚠️

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