feat(TaskScheduler): introduce semaphore-based task scheduler (Epic 3, Story 3.1)

[edelauna]

Related GitHub Issue

Closes: #358

Description

Introduces TaskScheduler, a semaphore-based concurrency gate that wraps the existing TaskSemaphore utility, and wires it into ClineProvider as the single launch path for all tasks.

Key changes:

• TaskScheduler (src/core/task/TaskScheduler.ts): thin wrapper around TaskSemaphore; schedule(task, run) acquires a permit, checks task.abort || task.abandoned before executing, and always releases in finally. Ships at maxConcurrency=1 (identical to current serial behaviour — raising it later enables fan-out without touching gate logic). cancelQueued() is called from ClineProvider.dispose() to drain the semaphore on teardown.

• Task.run() (src/core/task/Task.ts): awaitable twin of Task.start(); returns the in-flight _runPromise if already running, or a resolved promise if _started is set (guards against double-invocation from constructor, start(), or a second run() call). ClineProvider now calls task.run() through the scheduler instead of task.start() directly.

• ClineProvider (src/core/webview/ClineProvider.ts): holds a TaskScheduler instance; all task launch sites (createTask, delegateParentAndOpenChild) use void this.taskScheduler.schedule(task, () => task.run()). dispose() calls cancelQueued() before clearing the stack.

• Tests: TaskScheduler.spec.ts (8 cases: immediate run, serial queuing, parallel at maxConcurrency=2, permit release on throw, cancelQueued, abort guard, abandoned guard, default concurrency); Task.dispose.test.ts gains a Task.run() idempotency describe (3 cases); provider-delegation.spec.ts and single-open-invariant.spec.ts updated to carry taskScheduler on provider stubs.

• AGENTS.md: adds an ESLint Suppressions section documenting that counts must never increase, when as any is acceptable, and the prune-suppressions maintenance command. eslint-suppressions.json count for Task.dispose.test.ts reduced from 8 → 3.

No behaviour change at maxConcurrency=1 — tasks still run serially. The scheduler is the expand step of an expand-contract migration; fan-out (Story 3.2b) raises the limit without changing this gate logic.

Test Procedure

# Unit tests
pnpm --filter=zoo-code test -- --run core/task/__tests__/TaskScheduler.spec.ts
pnpm --filter=zoo-code test -- --run core/task/__tests__/Task.dispose.test.ts
pnpm --filter=zoo-code test -- --run __tests__/provider-delegation.spec.ts
pnpm --filter=zoo-code test -- --run __tests__/single-open-invariant.spec.ts

# Types + lint
pnpm --filter=zoo-code check-types
pnpm --dir src exec eslint --max-warnings=0 core/task/TaskScheduler.ts core/task/Task.ts core/webview/ClineProvider.ts

Pre-Submission Checklist

• Issue Linked: Closes [Epic 3] TaskScheduler + Subtask Fan-out #358
• Scope: TaskScheduler + Task.run() only; no fan-out logic yet (Story 3.2b is next)
• Self-Review: Done
• Testing: Unit tests added for scheduler, idempotency, and provider integration
• Visual Snapshot: N/A — no UI changes
• Documentation Impact: AGENTS.md updated with ESLint suppression guidance
• Contribution Guidelines: Read and agreed

Summary by CodeRabbit

• New Features

  • Added task scheduling to control concurrent task execution.
  • Added promise-based task launching with idempotent repeated calls.
  • Queued tasks can now be canceled, while active tasks continue safely.
  • Tasks are prevented from starting after disposal or when marked inactive.

• Bug Fixes

  • Improved task delegation sequencing and rollback behavior.
  • Ensured scheduling permits are released when task execution fails.

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📝 Walkthrough

Walkthrough

Adds idempotent promise-based task execution, a semaphore-backed TaskScheduler, and provider integration for scheduled task startup and shutdown cancellation. Tests now validate concurrency, ordering, rollback, and updated task mocks.

Changes

Task scheduling

Layer / File(s)	Summary
Promise-based task execution src/core/task/Task.ts, src/core/task/__tests__/Task.dispose.test.ts, AGENTS.md, src/eslint-suppressions.json	Task.run() tracks and reuses its execution promise; disposal tests use typed event constants and cover idempotency, while lint guidance and suppression counts are updated.
Concurrency scheduler src/core/task/TaskScheduler.ts, src/core/task/__tests__/TaskScheduler.spec.ts	TaskScheduler limits concurrency, skips aborted or abandoned tasks, releases permits on completion or failure, and cancels queued work.
Provider scheduling integration src/core/webview/ClineProvider.ts	Task creation and delegated child execution use TaskScheduler.schedule, and provider disposal cancels queued tasks.
Provider flow validation src/__tests__/provider-delegation.spec.ts, src/__tests__/single-open-invariant.spec.ts	Provider mocks and assertions now cover scheduled run() calls, microtask timing, execution ordering, and rollback behavior.

Estimated code review effort: 3 (Moderate) | ~25 minutes

Possibly related PRs

• Zoo-Code-Org/Zoo-Code#675: Provides the related TaskSemaphore concurrency primitive used by the scheduler.
• Zoo-Code-Org/Zoo-Code#691: Modifies the same delegation flow and atomic persistence ordering.
• Zoo-Code-Org/Zoo-Code#692: Updates the same provider delegation lifecycle and related tests.

Suggested labels: awaiting-review

Suggested reviewers: hannesrudolph

Sequence Diagram(s)

sequenceDiagram
  participant ClineProvider
  participant TaskScheduler
  participant Task
  ClineProvider->>TaskScheduler: schedule(task, task.run)
  TaskScheduler->>Task: run()
  Task-->>TaskScheduler: resolve or reject
  TaskScheduler->>TaskScheduler: release concurrency permit

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🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Title check	✅ Passed	The title clearly matches the main change: adding a semaphore-based TaskScheduler.
Description check	✅ Passed	The description follows the template and includes the linked issue, implementation summary, test procedure, and checklist.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch issue/368

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[codecov]

Codecov Report

❌ Patch coverage is 84.84848% with 5 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
src/core/webview/ClineProvider.ts	69.23%	2 Missing and 2 partials ⚠️
src/core/task/Task.ts	88.88%	0 Missing and 1 partial ⚠️

📢 Thoughts on this report? Let us know!

[coderabbitai]

Actionable comments posted: 1

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In `@src/core/webview/ClineProvider.ts`:
- Around line 3191-3199: Update createTaskWithHistoryItem so its implicit task
startup uses taskScheduler.schedule(task, () => task.run()) instead of invoking
task.run directly, preserving the startTask: false opt-out and matching
createTask’s concurrency-gated startup behavior.

🪄 Autofix (Beta)

Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

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ℹ️ Review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro Plus

Run ID: 9116becd-95dc-49c3-a4a2-4822b1a6ac95

📥 Commits

Reviewing files that changed from the base of the PR and between 2db2af0 and 7fc3e4b.

📒 Files selected for processing (9)

• AGENTS.md
• src/__tests__/provider-delegation.spec.ts
• src/__tests__/single-open-invariant.spec.ts
• src/core/task/Task.ts
• src/core/task/TaskScheduler.ts
• src/core/task/__tests__/Task.dispose.test.ts
• src/core/task/__tests__/TaskScheduler.spec.ts
• src/core/webview/ClineProvider.ts
• src/eslint-suppressions.json