Isolate Workspace

Isolate Workspace

Give feature work an isolated workspace with a verified-clean starting point. Order of preference: detect isolation that already exists → the harness's native workspace tool → a manual git worktree fallback. Never fight the harness.

Step 0 — Detect and get consent

Check whether you are already inside a linked worktree:

GIT_DIR=$(cd "$(git rev-parse --git-dir)" && pwd -P)
GIT_COMMON=$(cd "$(git rev-parse --git-common-dir)" && pwd -P)

• GIT_DIR != GIT_COMMON → likely a linked worktree, but guard against submodules first: if git rev-parse --show-superproject-working-tree prints a path, you are in a submodule — treat it as a normal checkout. Otherwise you are already isolated: report the path and branch, skip creation, go to Step 2.
• GIT_DIR == GIT_COMMON → normal checkout. If the user has a stated worktree preference, honor it silently. If not, ask: "Want me to set this up in an isolated worktree so your current branch stays untouched?" Declined → work in place, go to Step 2.

Done when: you know which of the three cases you are in, and you have consent if creating.

Step 1 — Create the workspace

1a. Native tool first. If the harness provides a workspace/worktree mechanism (a tool named like EnterWorktree, a /worktree command, a --worktree flag), use it and go to Step 2. A native tool manages placement, branching, and cleanup itself; creating a manual worktree alongside it leaves phantom state the harness can't see. Only fall through when no native tool exists.

1b. Git fallback. Pick the directory by priority:

1. An explicit user instruction — always wins
2. An existing .worktrees/ at the repo root
3. An existing worktrees/ (if both exist, .worktrees/ wins)
4. An existing .isolate-workspace/ (legacy — reuse it; do not mint a second parent)
5. An existing isolate-workspace/ (legacy)
6. None of the above → create .worktrees/

Bind the chosen directory to $DIR and use it in every command below — the priority list above is real only if the commands honor it:

DIR=.worktrees   # or DIR=worktrees / a legacy isolate-workspace dir if that existing dir was selected above

Before creating anything inside a project-local directory, you MUST confirm it is git-ignored. Leave the entry as an uncommitted working-tree change — git honors it immediately, and committing .gitignore here would write a commit to the user's current branch, the exact thing this skill promises not to touch:

git check-ignore -q "$DIR" || printf '%s/\n' "$DIR" >> .gitignore

Then create and enter:

git worktree add "$DIR/<branch-name>" -b "<branch-name>"

If creation fails on a sandbox/permission error, tell the user and work in place instead.

Done when: you are in the workspace (or have reported why not).

Step 2 — Install dependencies

Auto-detect the package manager from lockfiles/manifests and run its install: pnpm-lock.yaml → pnpm, bun.lock* → bun, yarn.lock → yarn, package-lock.json/bare package.json → npm, Cargo.toml → cargo build, uv.lock → uv, poetry.lock → poetry, requirements.txt → pip, go.mod → go mod download. No manifest → skip.

Step 3 — Clean baseline

Run the test suite using the command in docs/agents/project.md (missing → say so, suggest configure-repo, and use the ecosystem's default runner).

• Baseline green → proceed.
• Baseline red → STOP and ask the user before proceeding. Starting on a failing baseline makes it impossible to tell your bugs from pre-existing ones.

Report

Workspace ready at <absolute path> (branch <name>)
Baseline: <N> tests passing, 0 failures
Ready to start <task>.

Red Flags — Never

• Create a worktree when Step 0 found you already in one
• Use git worktree add when a native tool exists
• Create a project-local worktree directory without the ignore check
• Skip the baseline run, or continue past a red baseline without asking