Use worktree-per-task when tasks within a plan are independent enough that you want:

• Per-task rollback — a failing task can be discarded without touching the others.
• Parallel CI validation — each task's merge commit is separately bisectable.

Cost: every isolated task multiplies CI minutes. Mark only tasks that are genuinely independent; sequential tasks that build on each other should run directly.

• development-lifecycle plugin installed.
• A .harness/project.json in your repo (created by /setup).
• The isolation.mode field set to worktree-per-task in that file.

In .harness/project.json, add or update the isolation block:

{
  "isolation": {
    "mode": "worktree-per-task"
  }
}

This tells /work's step 2.5 to check each task for an isolation flag before executing it.

In your .harness/PLAN.md, add **Isolated:** true to each task that should run in its own worktree:

### 3. Refactor auth module — Status: [ ]
**Isolated:** true
Rewrite `src/auth/` to the new interface contract.

Leave the flag off tasks that must run sequentially or depend on a preceding task's output.

/work

When /work reaches a task marked **Isolated:** true, step 2.5 fires:

1. A per-task worktree is spawned: worker/<plan-slug>-task-<N>.
2. Steps 3–9 (implement → commit) run inside the task worktree.
3. After the task commits, the branch merges back into the plan's main context with git merge --no-ff.
4. The task worktree and branch are pruned.
5. The task loop continues in the plan's main context.

For non-isolated tasks, step 2.5 exits 1 and /work proceeds directly — no worktree spawned.

• Knob separation — per-task isolation is independent of per-plan integration. Task worktrees merge back into the plan branch; the plan-level integration setting (step 12) still controls whether the finished plan lands as a PR or a direct push.
• Authority is operator-declared — the agent never auto-marks tasks isolated. Only tasks with **Isolated:** true in PLAN.md get a worktree.
• Re-audit trigger — if the per-task override rate stays near zero across several plans, the N× CI cost isn't earning its keep. Consider reverting to worktree-per-plan or direct.

• Run a named plan — plan-level worktree isolation: /work's own auto-spawn, gated on isolation.mode: worktree-per-plan.
• Run a coordinator-directed worker team — multi-worker parallel execution.
• Named plans — how plan slugs and .harness/active-plan bind workers to plans.
• Development Lifecycle — full primitive reference.