release: cut v0.2.19 (PRP-34 batch parallel execution)

[w7-mgfcode]

Summary

• PRP-34 — Batch parallel execution (PR feat(batch,ui): activate max_parallel + cooperative cancellation (PRP-34) #291, closes feat(batch): activate max_parallel + cooperative cancellation (PRP-34) #290): bounded asyncio.Semaphore + TaskGroup runner with cooperative cancellation. New DELETE /batch/{batch_id} endpoint (200/404/409/504), BatchSubmitResponse.effective_max_parallel computed-field, slider UX + Cancel AlertDialog on visualize/batch.tsx. No Alembic migration — activates the three forward-compat columns PRP-33 shipped on batch_job.
• Chore — uv.lock refresh to v0.2.18 (PR chore(repo): refresh uv.lock to v0.2.18 (#239) #289, chore: uv.lock version field lags released version (0.2.8 → 0.2.15) #239).
• CI — dependabot bump of github/codeql-action 4.35.5 → 4.36.0 (PR ci: bump github/codeql-action from 4.35.5 to 4.36.0 #286).

Pre-1.0 SemVer (feat: → PATCH per release-please-config.json) — release-please will open a Release PR on main bumping to v0.2.19.

Test plan

• All five validation gates green on tip 36fff6e (CI + Schema Validation both success)
• 1466 unit + 15 batch integration tests passing locally
• Frontend 121 vitest cases passing
• Merge via GitHub web UI (NOT gh pr merge --merge — see docs/_base/RUNBOOKS.md → "release-please skipped the bump after a dev → main merge")
• Verify release-please opens a chore(main): release 0.2.19 PR on main
• Merge the Release PR → tag v0.2.19
• Back-merge main → dev with --merge (not squash)

Summary by CodeRabbit

Release Notes

• New Features

  • Added configurable concurrency limit for batch execution via a "Max parallel" slider in the batch submission form
  • Added "Cancel batch" button with confirmation dialog to stop in-flight batch jobs
  • Batch cards now display execution status with running/completion counts and effective parallelism

• Improvements

  • Enhanced batch UI with better status visibility and progress tracking
  • Batch cancellation requests now include timeout protection to prevent indefinite waits

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Caution

Review failed

Pull request was closed or merged during review

📝 Walkthrough

Walkthrough

This PR implements PRP-34 — Batch Parallel Execution, transitioning from serial batch execution to bounded-concurrency async processing with cooperative cancellation. The implementation adds a new app/features/batch/runner.py using asyncio.Semaphore and asyncio.TaskGroup, a DELETE /batch/{batch_id} cancellation endpoint with configurable drain timeout, frontend max-parallel slider and cancel-button UI, and comprehensive unit, integration, and chaos tests.

Changes

Batch Parallel Execution (PRP-34)

Layer / File(s)	Summary
PRP-34 Specification & Documentation PRPs/PRP-34-batch-parallel-execution.md, PRPs/ai_docs/asyncio-taskgroup-cancellation.md	Design documents for bounded-concurrency batch execution with asyncio semantics verification, error handling, and implementation blueprint.
Configuration & Error Infrastructure .env.example, app/core/config.py, app/core/exceptions.py, app/core/problem_details.py	New batch settings (batch_global_max_parallel=4, batch_cancel_drain_timeout_seconds=30), GatewayTimeoutError exception, and RFC 7807 error type URI for drain timeout.
Domain Model & State Transitions app/features/batch/models.py, app/features/batch/tests/test_models.py	Batch item state machine now allows RUNNING → CANCELLED transition; new TERMINAL_BATCH_STATES constant for cancel endpoint validation.
Asyncio Batch Runner app/features/batch/runner.py	Core module: asyncio.Semaphore(effective_parallel) inside asyncio.TaskGroup, per-item AsyncSession, cooperative cancellation via asyncio.Event, in-memory registry, cancel/drain/completion helpers, and DB state transitions.
Runner Unit & Orchestration Tests app/features/batch/tests/test_runner.py	Nine tests validating semaphore concurrency cap, global-cap clamping, sibling failure isolation, pending-child cancellation, running-child cancellation, and drain/registry coordination.
Service Integration & Response Schema app/features/batch/service.py, app/features/batch/schemas.py	Rewire BatchService.submit to call runner.run_batch instead of picker loop; add per-child session maker; persist effective_max_parallel to result_summary; add computed response field.
DELETE Cancellation Endpoint & Tests app/features/batch/routes.py, app/features/batch/tests/test_routes_cancel.py	New DELETE /batch/{batch_id} route: validates existence/non-terminal status (404/409 RFC 7807), fires cooperative cancellation, awaits bounded drain (504 on timeout), returns settled parent. Four integration tests: 404 unknown, 409 terminal, 200 clean drain, 504 timeout.
Chaos & Regression Tests app/features/batch/tests/test_runner_chaos.py	Integration tests: mid-flight cancellation with no orphaned RUNNING items, end-to-end batch completion via HTTP with effective_max_parallel verification.
Frontend Infrastructure frontend/package.json, frontend/src/components/ui/slider.tsx, frontend/src/types/api.ts, frontend/src/hooks/use-batches.ts, frontend/src/hooks/use-batches.test.ts	Radix UI slider dependency and component wrapper; API type updates (TERMINAL_BATCH_STATES, effective_max_parallel); useCancelBatch mutation hook with RFC 7807 error handling.
Batch Page UI frontend/src/pages/visualize/batch.tsx	Max-parallel slider input, cancel button with AlertDialog confirmation, running/completion/effective-parallel badges, and improved numeric safety checks.
CI Maintenance .github/workflows/dependency-check.yml	CodeQL Action upgraded to v4.36.0.

Estimated code review effort

🎯 4 (Complex) | ⏱️ ~60 minutes

Possibly related issues

• #280: Extends the batch-runner vertical from PRP-33 MVP with full parallel execution and cancellation orchestration.

Suggested reviewers

• w7-learn

Poem

🐰 Bounded rabbits now fan out with care,
A semaphore guards the pool we share,
Cooperative waves say "cancel please,"
And drain waits gentle, never with squeeze.
Slider and button make chaos serene,
The finest batch pipeline I've seen! ✨

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 66.67% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The pull request title 'release: cut v0.2.19 (PRP-34 batch parallel execution)' clearly reflects the main change: a version bump release cut for v0.2.19 that implements PRP-34 batch parallel execution.
Linked Issues check	✅ Passed	The PR implements all core acceptance criteria from issue #290: runner.py with bounded asyncio.Semaphore, DELETE endpoint with RFC 7807 responses, effective_max_parallel computed field, frontend Slider and AlertDialog, default settings, tests, and no new migrations.
Out of Scope Changes check	✅ Passed	All changes are within scope: batch runner implementation, delete endpoint, configuration, frontend updates, tests, and documentation all directly support PRP-34. GitHub Actions version bump and dependency updates are maintenance-related and necessary.

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✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch dev

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