---
name: parallelizing-subsystem-work
user-invocable: true
description: Use whenever 2 or more subsystems under `docs/subsystems/` each have completed requirements + basic design and the user wants them implemented concurrently in isolated git worktrees. Trigger on phrases like "サブシステムを並列で実装したい", "複数の基本設計を同時に進めて", "worktree で並列化して", "parallelize these subsystems", "implement these in parallel worktrees". This skill MUST halt if any candidate pair has a dependency, touches shared main-* files, or if the repo is dirty; it MUST NOT invoke any `superpowers:*` skill (including `superpowers:using-git-worktrees` and `superpowers:dispatching-parallel-agents`).
---

# parallelizing-subsystem-work

Conformance keywords: [RFC 2119](https://www.rfc-editor.org/rfc/rfc2119) / [RFC 8174](https://www.rfc-editor.org/rfc/rfc8174). **MUST NOT** invoke any `superpowers:*` skill (see `../spec-coexist-router/references/independence.md`).

## Purpose

Drive concurrent `spec-coexist:implementing-from-spec` runs for multiple **independent** subsystems in isolated git worktrees, then consolidate the results. The core value is the **isolation check** — refusing to parallelize work that cannot be safely parallelized — not the mechanical act of creating worktrees.

## When to Trigger

Trigger when **both** apply:

- `docs/subsystems/` contains ≥ 2 directories with both `*-requirements.md` and `*-design.md` marked ready.
- The user explicitly asks for parallel, concurrent, or worktree-based implementation.

Do **NOT** trigger for single-subsystem work (use `spec-coexist:implementing-from-spec` directly), or while the spec is still being drafted.

## References

- `references/isolation-rules.md` — the independence decision procedure: when two subsystems MAY run in parallel and when they MUST NOT.
- `references/worktree-layout.md` — naming, directory, and branch conventions for the worktrees this skill creates.
- `references/consolidation.md` — how to merge back, resolve conflicts, topological ordering, and retire worktrees.
- `references/subagent-dispatch.md` — prompt template, agent count limits, and result aggregation format for dispatching parallel agents.
- `references/partial-failure.md` — playbook for when a worktree fails: continuation decisions, rollback conditions, evidence merge rules, and recovery.

## Shared Scripts

- `../_shared/scripts/subsystem_deps.sh` — print a dependency edge list for subsystems under `docs/subsystems/`.
- `../_shared/scripts/make_worktree.sh <subsystem-id>` — create `../worktrees/{subsystem-id}` on branch `parallel/{subsystem-id}`. Refuses if the repo is dirty.
- `../_shared/scripts/cleanup_worktree.sh <subsystem-id>` — remove the worktree and delete its branch after integration.
- `../_shared/scripts/detect_worktree_conflicts.sh [id ...]` — detect file-level conflicts between active worktrees at runtime. Exit 0 = clean, exit 1 = conflicts found.

## Ordered Steps

1. **Repo cleanliness check.** `git status --porcelain` **MUST** be empty. **HALT** otherwise — parallel work on a dirty tree silently mixes changes.
2. **Extract dependency graph.** Run `subsystem_deps.sh` and read its edge list.
3. **Select an independent set.** Per `references/isolation-rules.md`, pick the largest set of subsystems with no mutual edges AND no edges to any file under `docs/main-*`. **HALT** with the violating pair if no valid set of size ≥ 2 exists.
4. **Confirm the set with the user (HALT).** Present the chosen subsystems, the rejected ones with reasons, and the planned worktree paths. Wait for explicit "proceed".
5. **Create worktrees.** For each chosen subsystem, run `make_worktree.sh <id>`. If any call fails, **HALT** and roll back previously-created worktrees via `cleanup_worktree.sh`.
6. **Dispatch agents per worktree.** Per `references/subagent-dispatch.md`, launch one agent per worktree in a single message (concurrent). Each agent runs `implementing-from-spec` + `verification-before-completion` and reports its commit SHA + evidence paths.
7. **Evaluate results.** If any agent failed, follow `references/partial-failure.md` to decide continue vs. halt. Run `detect_worktree_conflicts.sh` before proceeding.
8. **Consolidate.** Record `PRE_CONSOLIDATION_SHA`. Per `references/consolidation.md`, merge branches in topological order (provider before consumer; ties broken by ascending id). If a merge conflicts, **HALT** and record in `docs/evidence/parallel-conflict-{YYYY-MM-DD}.md`.
9. **Cleanup.** Run `cleanup_worktree.sh` for each integrated worktree.
10. **Report.** Emit integrated subsystem list, per-subsystem evidence paths, skipped/failed subsystems, any recorded conflicts, and a `Review:` outcome line.

## Hard Constraints

- **MUST NOT** include any subsystem whose design touches a shared `docs/main-*.md` file in the parallel set.
- **MUST NOT** proceed with a dirty working tree.
- **MUST NOT** skip the per-worktree `verification-before-completion` gate.
- **MUST NOT** use `git worktree remove --force` unless the user explicitly confirms in step 7 rollback.
- Full rationale: `references/isolation-rules.md`.

## Flow

```mermaid
flowchart TD
    Start([≥2 ready subsystems]) --> Clean{Repo clean?}
    Clean -- No --> Halt1([HALT])
    Clean -- Yes --> Dep[subsystem_deps.sh]
    Dep --> Set{Independent set<br/>of size ≥2?}
    Set -- No --> Halt2([HALT: report blocking edge])
    Set -- Yes --> Conf{User confirms?}
    Conf -- No --> End1([Abort])
    Conf -- Yes --> MK[make_worktree.sh per id]
    MK --> Disp[Dispatch agents per worktree<br/>— subagent-dispatch.md]
    Disp --> Eval{All agents<br/>succeeded?}
    Eval -- No --> PF[partial-failure.md<br/>playbook]
    PF --> CanCont{Continue with<br/>successful?}
    CanCont -- No --> HaltPF([HALT — return to user])
    CanCont -- Yes --> DC
    Eval -- Yes --> DC[detect_worktree_conflicts.sh]
    DC --> DCR{Conflicts?}
    DCR -- Yes --> Halt3([HALT: record false negative])
    DCR -- No --> Cons[Consolidate in<br/>topological order]
    Cons --> CL[cleanup_worktree.sh per id]
    CL --> End([Done — report])
```