using-git-worktrees

OPTIONAL. Per-task filesystem isolation for parallel agent work — opt-in only, never the default path. Routed to by subagent-driven-development and dispatching-parallel-agents when, and only when, the caller requests isolation. If no isolation is requested, this skill does not run; parallel units share the working tree under their own discipline.

Isolation is convenience, not soul. It lets concurrent units edit files without collision. It changes nothing about the gates — the consolidated work still clears commit-gate and the single finishing-a-development-branch terminal step, run by the caller. What it MUST NOT do is multiply that terminal step into one PR per unit.

Pre-flight

Read these, or STOP and surface the gap — never guess:

• {{PROJECT_DIR}}/.codearbiter/CONTEXT.md — confirm the repo is a git repo and the base/working branch.
• The discovered authoritative spec/plan pair for the caller's pipeline. Use its exact selected plan for the parallel unit list. Re-run the private bridge resolver _resolve_workflow_pair with the trusted project root and pipeline slug rather than reconstructing either path. For an HTML pair, load {{PLUGIN_ROOT}}/includes/artifacts.md and obtain HTML task and path records only through the installed engine identity, index, and symbol-scoped read operations. For a Markdown pair, use its existing Markdown task table. Worktree planning must not create, convert, or consult a counterpart.

Confirm the caller passed an explicit isolation opt-in AND the parallel unit list from the exact selected plan. Absent either, do not stand up worktrees.

Phase 1 — Provision · gate: BLOCK

Stand up one worktree per parallel unit. For each unit, create a worktree on a fresh branch off the current base, under a dedicated parent directory outside the main working tree (e.g. ../.codearbiter-worktrees/<slug>):

• One worktree, one branch, one unit. Never share a worktree across units.
• Branch name MUST be unique and traceable to its unit's task ID.
• Record each worktree path and branch in a dedicated manifest {{PROJECT_DIR}}/.codearbiter/.worktrees.json (gitignored scratch — NOT the open-tasks.md backlog) so a crash leaves no untracked isolation.

Gate: every unit has a distinct worktree on a distinct branch, all rooted at the same clean base, all recorded. A reused branch or a missing record does not pass.

Phase 2 — Isolated work · gate: BLOCK

Each parallel unit works entirely inside its own worktree. Dispatch is unchanged — the caller still dispatches its author and reviewer agents; they simply operate on the isolated path.

• A unit MUST NOT read or write outside its assigned worktree.
• A unit MUST NOT touch main or any other unit's branch.
• All implementation inside a worktree still flows through tdd — isolation is not a TDD bypass.

Gate: each unit's work is contained to its own worktree, with no cross-worktree or base-branch writes.

Phase 3 — Fold back · gate: BLOCK

Integrate each isolated unit's work back onto the caller's single working branch — do NOT finish each unit on its own. Per unit, in order:

1. Confirm the unit was accepted by the caller (its per-task review and verification passed in subagent-driven-development, or its result cleared the funnel in dispatching-parallel-agents). An unaccepted unit does not fold back.
2. Integrate its branch onto the caller's working branch (merge or rebase), resolving any conflict here, in the open. Never integrate onto main or the default branch.

The consolidated working branch then takes the caller's normal single exit — ONE commit-gate pass and ONE finishing-a-development-branch decision, run by the caller, not per unit. This skill integrates; it never opens N PRs or finishes N branches. A unit that cannot integrate cleanly is surfaced as a conflict for resolution — never force-merged, never dropped silently.

Gate: every accepted unit integrated onto the caller's working branch with conflicts resolved; no per-unit PR or finish was opened.

Phase 4 — Teardown · gate: BLOCK

Remove every worktree this skill created, prune its administrative metadata, and clear the manifest at {{PROJECT_DIR}}/.codearbiter/.worktrees.json. A unit whose branch was integrated onto the working branch (Phase 3) has its worktree torn down; an unaccepted or abandoned unit's worktree and branch are removed together.

Gate: zero worktrees created by this skill remain, and the manifest is empty. An orphaned worktree is a failure.

Hard rules

• MUST NOT run on the default path — isolation requires an explicit caller opt-in.
• MUST NOT share a worktree or a branch across parallel units.
• MUST NOT let a unit read or write outside its assigned worktree, or touch main.
• MUST NOT open a per-unit PR or run finishing-a-development-branch per unit — integrate accepted units onto the caller's working branch, which takes the single commit-gate + finishing exit.
• MUST NOT leave an orphaned worktree behind — every worktree this skill creates is torn down before the skill returns.