[Fix] Subtasks fail to return when users work across windows by zoomote[bot] · Pull Request #1471 · Zoo-Code-Org/Zoo-Code

zoomote · 2026-08-31T23:26:11Z

Created by Roomote. Follow up by mentioning @roomote, in the web UI, or in Discord.

What changed

Serializes parent delegation and completion across VS Code extension hosts with one authoritative parent transition lock.
Rejects stale child completion before metadata, conversation history, teardown, or parent resume can overwrite a newer handoff.
Adds exact rollback for partial pair writes and deterministic cross-instance regression coverage, including a barrier-controlled re-delegation schedule.

Why this change was made

Multiple Zoo Code windows could interleave an old child completion with a newer delegation, orphaning the newer child and leaving attempt_completion unable to return. The failure was reproduced deterministically and modeled with SPIN.

Impact

Subtasks now return only to the parent handoff that still owns them. Concurrent mode, model, start, stop, and delegation activity in another window cannot replace a newer handoff with stale completion state or history.

Related PRs

Zoo Code Docs #55

Closes #1469

github-actions · 2026-08-31T23:26:22Z

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codecov · 2026-08-31T23:31:15Z

Codecov Report

❌ Patch coverage is 74.21875% with 66 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
src/core/webview/ClineProvider.ts	73.37%	24 Missing and 21 partials ⚠️
src/core/task-persistence/TaskHistoryStore.ts	73.84%	10 Missing and 7 partials ⚠️
src/core/task/Task.ts	77.77%	0 Missing and 2 partials ⚠️
src/utils/safeWriteJson.ts	83.33%	2 Missing ⚠️

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edelauna · 2026-08-31T23:48:03Z

@CodeRabbit reveiw

coderabbitai · 2026-08-31T23:49:58Z

@edelauna I will review the changes in #1471.

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coderabbitai · 2026-08-31T23:50:19Z

📝 Walkthrough

Summary by CodeRabbit

Bug Fixes
- Improved delegation handoffs to prevent stale updates and conflicting changes across concurrent processes.
- Added rollback protection when completing a delegated task fails.
- Ensured task messages and history remain consistent during delegation recovery and cancellation.
Reliability
- Added safer file locking for task history updates.
- Preserved retry availability when delegation handoffs cannot be completed.
Tests
- Expanded coverage for cross-instance delegation, locking, rollback, and stale completion scenarios.

Walkthrough

Task history persistence now coordinates cross-process locks and guarded pair updates. Delegation resume uses parent-first locking, stale-owner validation, rollback, and deferred in-memory handoff work. Task APIs support skipping message persistence during delegated-child cleanup. Tests cover stale completion, rollback, and lock-held handoffs.

Changes

Delegation concurrency

Layer / File(s)	Summary
Atomic task-history locking and rollback `src/utils/safeWriteJson.ts`, `src/core/task-persistence/TaskHistoryStore.ts`, `src/core/task-persistence/__tests__/TaskHistoryStore.crossInstanceDelegation.spec.ts`, `src/core/task-persistence/__tests__/TaskHistoryStore*.spec.ts`, `src/__tests__/delegation-concurrent.spec.ts`	`lockJsonFile` provides reusable advisory locks. `TaskHistoryStore` supports disk guards, caller-held locks, ordered pair updates, rollback, and locked callbacks. Cross-instance tests cover stale completion, failed child writes, and lock-held redelegation.
Parent-child handoff integration and validation `src/core/webview/ClineProvider.ts`, `src/core/task/Task.ts`, `src/core/task/__tests__/Task.persistence.spec.ts`, `src/__tests__/helpers/provider-stub.ts`, `src/__tests__/history-resume-delegation.spec.ts`, `src/__tests__/nested-delegation-resume.spec.ts`, `src/__tests__/provider-delegation.spec.ts`, `src/eslint-suppressions.json`	Delegation and resume flows run under the parent task lock. Resume revalidates parent ownership before updates and rolls back on child-write failure. Task history replacement and child abort can skip persistence. Test stubs and assertions match the new contracts.

Estimated code review effort: 4 (Complex) | ~45 minutes

Merge Risk: 🟠 High · up to c086b

This PR improves cross-window subtask handoffs, but unresolved lock-order failures and unguarded ownership transitions can still cause subtasks to be orphaned, parent progress to fail to persist, or resumed conversations to become inconsistent. The completion and abandonment paths should be hardened before merge.

Suggested reviewers: edelauna

Caution

Pre-merge checks failed

Please resolve all errors before merging. Addressing warnings is optional.

Ignore

❌ Failed checks (1 error, 1 warning)

Check name	Status	Explanation	Resolution
Trust And Persistence Invariants	❌ Error	FAIL: `reopenParentFromDelegation` commits the parent and child history records before it persists the parent conversation files. `atomicUpdatePair` sets both caches after the two history writes at `s…	Do not commit the parent/child completion state until the parent UI and API message writes succeed, while retaining the parent ownership guard. Persist the prepared message files after revalidating the parent under the held parent lock and …
Regression Evidence	⚠️ Warning	The new `persist: false` behavior lacks focused coverage at the `Task` layer. `Task.overwriteClineMessages` and `Task.overwriteApiConversationHistory` now skip persistence when this option is set (`sr…	Add focused `Task` persistence tests for both overwrite methods with `{ persist: false }`. Assert that each method updates in-memory state and does not call its corresponding save method. Add at least one delegation test assertion that `reo…

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly identifies the primary fix: subtasks failing to return when users work across windows.
Description check	✅ Passed	The description links issue `#1469` and clearly explains the race condition, implementation, impact, and regression coverage. It does not include a detailed Test Procedure or the template checklist, but…
Linked Issues check	✅ Passed	The changes address issue `#1469` by adding cross-instance locking, parent ownership revalidation, stale-completion rejection, rollback handling, and deterministic two-store regression tests. Existing c…
Out of Scope Changes check	✅ Passed	The code changes remain focused on cross-window delegation consistency, task persistence locking, related task lifecycle behavior, and regression tests. No unrelated implementation changes are evident…
Docstring Coverage	✅ Passed	Docstring coverage is 83.33% which is sufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 6 functions across 13 files. (1 skipped: 1 …

Full details: Description check

Explanation

The description links issue #1469 and clearly explains the race condition, implementation, impact, and regression coverage. It does not include a detailed Test Procedure or the template checklist, but the substantive description is complete.

Full details: Linked Issues check

Explanation

The changes address issue #1469 by adding cross-instance locking, parent ownership revalidation, stale-completion rejection, rollback handling, and deterministic two-store regression tests. Existing completion and interrupted-child behavior is also updated and covered.

Full details: Out of Scope Changes check

Explanation

The code changes remain focused on cross-window delegation consistency, task persistence locking, related task lifecycle behavior, and regression tests. No unrelated implementation changes are evident.

Full details: Docstring Coverage

Explanation

Docstring coverage is 83.33% which is sufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 6 functions across 13 files. (1 skipped: 1 unsupported.)

Full details: Regression Evidence

Explanation

The new persist: false behavior lacks focused coverage at the Task layer. Task.overwriteClineMessages and Task.overwriteApiConversationHistory now skip persistence when this option is set (src/core/task/Task.ts:1020-1024, 1183-1188), and the new handoff depends on that behavior at ClineProvider.ts:4283-4290. The delegation tests use mocked overwrite methods and only assert that they were called; they do not assert the { persist: false } argument or verify that disk-save methods are skipped. Task.persistence.spec.ts has no direct tests for either overwrite method. The existing saveMessages: false abort test does not cover this separate contract.

Resolution

Add focused Task persistence tests for both overwrite methods with { persist: false }. Assert that each method updates in-memory state and does not call its corresponding save method. Add at least one delegation test assertion that reopenParentFromDelegation passes { persist: false } to both overwrite calls.

Full details: Trust And Persistence Invariants

Explanation

FAIL: reopenParentFromDelegation commits the parent and child history records before it persists the parent conversation files. atomicUpdatePair sets both caches after the two history writes at src/core/task-persistence/TaskHistoryStore.ts:1218-1220, then invokes whileFirstFileLocked at line 1226. The callback in src/core/webview/ClineProvider.ts:4268-4277 calls saveTaskMessages and saveApiMessages, and both functions propagate filesystem errors. If a disk-full, permission, or transient I/O error occurs, the callback rejects after the parent is active and the child is completed. The pair code only rolls back when the second history write fails, so it does not roll back this callback failure. reopenParentFromDelegation rethrows non-stale errors at lines 4299-4306, leaves parentToResume unset, and cannot retry because the parent no longer awaits the child. The generated subtask_result and API tool_result therefore remain unpersisted, while the committed metadata prevents normal retry. This is a changed non-atomic persistence path with a plausible data-loss trigger.

Resolution

Do not commit the parent/child completion state until the parent UI and API message writes succeed, while retaining the parent ownership guard. Persist the prepared message files after revalidating the parent under the held parent lock and before the pair status transition, then run atomicUpdatePair only after those writes succeed. Alternatively, extend the transaction to roll back both history records and restore the prior message files when whileFirstFileLocked fails, and keep the parent available for a retry. Add a regression test that makes saveTaskMessages or saveApiMessages reject and verifies that the parent remains delegated, the child remains retryable, and no partial completion state is committed.

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🔧 ESLint

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src/__tests__/delegation-concurrent.spec.ts

ESLint skipped: missing config or dependency (missing-dependency). The ESLint configuration references a package that is not available in the sandbox.

src/__tests__/helpers/provider-stub.ts

ESLint skipped: the matched ESLint configuration already failed (missing-dependency).

src/__tests__/history-resume-delegation.spec.ts

ESLint skipped: the matched ESLint configuration already failed (missing-dependency).

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Actionable comments posted: 7

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Inline comments:
In
`@src/core/task-persistence/__tests__/TaskHistoryStore.crossInstanceDelegation.spec.ts`:
- Around line 228-229: Remove the unreliable single-microtask probe around
redelegationSettled in the cross-instance delegation test, or replace it with
sufficient scheduling turns for hostB.atomicReadAndUpdate to reach the lock
before asserting. Keep the existing order assertion as the proof that the parent
lock blocks hostB.

In `@src/core/task-persistence/TaskHistoryStore.ts`:
- Around line 134-135: Update the documentation for rollbackFirstOnSecondFailure
to state that rollback cannot restore a record after the first update moves its
status into a terminal state, such as completed, because the transition is
rejected. Keep the existing description and clarify that callers must only use
the option when the first update preserves a rollback-valid status transition.
- Around line 1150-1157: Update the atomicUpdatePair method documentation to
describe the stronger cross-process atomicity when holdFirstFileLock is enabled,
including that the first record’s lock spans both writes, onWrite, and
whileFirstFileLocked; document the relevant option combinations and retain the
weaker guarantee when the lock is not held.
- Around line 1036-1044: Move the JSDoc comment from withTaskFileLock to
atomicReadAndUpdate, preserving its description of on-disk updates, the
synchronous updater contract, and the missing-task cache exception.
- Around line 1045-1046: Update withTaskFileLock and the delegation path used by
ClineProvider.delegateParentAndOpenChild so atomicReadAndUpdate is not invoked
while the file lock is held and waiting for the store lock. Use a lock-safe
operation that reuses the already-held lock context without re-entering the
store lock, while preserving the callback’s task-file locking behavior.
- Line 1226: Document the contract for whileFirstFileLocked in the
atomicUpdatePair flow: it executes inside the non-reentrant withLock chain after
both writes and onWrite, so callbacks must not call upsert, atomicReadAndUpdate,
atomicUpdatePair, invalidate, or reconcile, and callback rejection may reject
atomicUpdatePair after durable changes. Keep the production callback and its
helpers free of store re-entry.

In `@src/core/webview/ClineProvider.ts`:
- Line 3873: Update delegateParentAndOpenChild and the
removeClineFromStack/abortTask save flow so the parent save does not reacquire
its already-held file lock. Reuse an existing-lock path by propagating
lockAcquired through saveClineMessages into TaskHistoryStore.upsert and
safeWriteJson, or move the save after the parent lock scope; preserve
persistence of the parent’s latest messages and avoid swallowing lock-related
save failures.

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📥 Commits

Reviewing files that changed from the base of the PR and between dfed27d and c086b13.

📒 Files selected for processing (14)

src/__tests__/delegation-concurrent.spec.ts
src/__tests__/helpers/provider-stub.ts
src/__tests__/history-resume-delegation.spec.ts
src/__tests__/nested-delegation-resume.spec.ts
src/__tests__/provider-delegation.spec.ts
src/core/task-persistence/TaskHistoryStore.ts
src/core/task-persistence/__tests__/TaskHistoryStore.crossInstanceDelegation.spec.ts
src/core/task-persistence/__tests__/TaskHistoryStore.reconciliation.spec.ts
src/core/task-persistence/__tests__/TaskHistoryStore.spec.ts
src/core/task/Task.ts
src/core/task/__tests__/Task.persistence.spec.ts
src/core/webview/ClineProvider.ts
src/eslint-suppressions.json
src/utils/safeWriteJson.ts

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📓 Path-based instructions (10)

Check persistence and lifecycle invariants: awaited atomic writes, rollback or explicit partial-failure behavior, cross-window state consistency, stale listeners/watchers, cancellation, idempotency, and safe restart/resume without lost or d...