Milestone 4: parallel execution - scheduler, worktrees, integrator (Tasks 19-21)

[inhaq]

This pull request was created by @kiro-agent on behalf of @inhaq 👻

Comment with /kiro fix to address specific feedback or /kiro all to address everything.
_{Learn about Kiro Web}

---

Summary

Completes Milestone 4 (Parallel execution) — Tasks 19, 20, 21.

Stacked PR. Based on m3-persistence (PR #6) → m2-runners (#5) → task-13-role-binding (#4). Merge in order #4 → #5 → #6 → this. Targets m3-persistence so the diff shows only Milestone 4.

Task 19 — Dependency-graph scheduler (engine/scheduler.ts)

• Runs tasks as a DAG with bounded concurrency (config.maxParallel); a task starts only once every dependency reaches an unblocking state, and dependents of an unsatisfied prerequisite are skipped transitively (nothing builds on a broken base).
• Validates the graph up front (duplicate / missing / self refs, cycles) → fails fast instead of deadlocking.
• session.runGoal now delegates ordering + parallelism to the scheduler (replacing the sequential pass), with seams for per-task workspaces and resume reuse.

Task 20 — Isolated worktrees (workspace/worktrees.ts)

• GitWorktreeManager gives each concurrent task its own git worktree on a dedicated branch cut from a base ref, commits its changes for integration, and tears the worktree down. git is injected (workspace/git.ts) so it's unit-testable and verified for real.

Task 21 — Integrator (engine/integrator.ts)

• Merges the per-task branches in a dedicated integration worktree (the repo checkout is never disturbed), in dependency order.
• A conflicting merge is aborted and surfaced with its conflicting file paths rather than force-resolved (Req 9.4); clean merges proceed.
• Runs full verification on the integrated tree. ok is true only when all merges were clean AND verification passed. Wired into runGoal behind opts.repoDir (+ config.useWorktrees).

Testing

• npm run typecheck clean.
• npm test: 119 passing (+13). Scheduler: ordering, parallelism-cap (peak ≤ max), transitive skip, resume reuse, graph validation. Worktrees + integrator run against real temp git repos: isolation, per-branch commit, clean multi-file merge + verification, and a real merge conflict surfaced with the offending file.

Note on end-to-end wiring

The worktree+integration path in runGoal is exercised at the module level with real git. A full runGoal end-to-end with worktrees needs a runner that actually writes files to the worktree (a real CLI/HTTP backend); the mock actors used in session tests don't touch the filesystem, so that combination isn't asserted here.

Summary by CodeRabbit

Release Notes

• New Features
  • Added parallel task execution with dependency-graph scheduling and configurable concurrency limits
  • Introduced isolated per-task git worktrees for independent task work with automatic branch management
  • Implemented automatic conflict detection during branch integration with detailed conflict reporting
  • Added full verification workflow for integrated changes
  • Enabled resume/checkpoint support to reuse prior task outcomes

[coderabbitai]

Important

Review skipped

Auto reviews are disabled on base/target branches other than the default branch.

🗂️ Base branches to auto review (1)

• '.*'

Please check the settings in the CodeRabbit UI or the .coderabbit.yaml file in this repository. To trigger a single review, invoke the @coderabbitai review command.

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro Plus

Run ID: ec746b79-2786-4b5b-b7fa-cb69045219fe

You can disable this status message by setting the reviews.review_status to false in the CodeRabbit configuration file.

Use the checkbox below for a quick retry:

• 🔍 Trigger review

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch m4-parallel

---

_{Comment @coderabbitai help to get the list of available commands and usage tips.}