Worktree Isolation

Trigger phrases: "worktree", "git worktree", "isolate the changes", "sandbox this work", "parallel file edits"

One rule: never let risky or parallel work run on top of uncommitted changes in the shared tree. A git worktree gives a second working copy of the same repo on its own branch — you experiment or fan out agents there, and the main tree (with your in-progress edits) is physically untouched. Throw the worktree away and nothing you cared about is lost.

Kit adaptation (local, .claude/): this exists because verification/fan-out subagents have discarded a session's uncommitted work by running a destructive git command over the shared tree. Those commands (reset --hard, clean -f, checkout -- ., restore) are §4.5-gated — but the real fix is to not put them near unsaved work. The Agent tool's isolation: "worktree" does this automatically for parallel mutating agents; reach for it there.

When to isolate

• Fan-out that writes files — two+ agents editing the same repo in parallel would collide; give each its own worktree.
• A throwaway experiment — you might keep it or bin it; a worktree makes "bin it" a one-liner, not a reset --hard.
• A dirty tree you can't commit yet — you have unsaved work but need to try something risky; isolate rather than stash-and-pray.
• Skip it for a single, in-place edit on a clean tree — a worktree is overhead there.

How

1. Detect — are you already in a worktree? [ "$(git rev-parse --git-dir)" != "$(git rev-parse --git-common-dir)" ] is true inside one; don't nest.
2. Create — git worktree add ../wt-<name> -b <branch> (new branch) or git worktree add ../wt-<name> <existing>. It shares the object store, so it's cheap.
3. Work there — cd into it; edits, builds, and agent runs stay local to that copy.
4. Fold back or discard — keep: commit on its branch, then merge. Discard: git worktree remove ../wt-<name> (add --force only if you mean to drop its changes).
5. Clean up — git worktree prune removes stale entries. Never leave orphaned worktrees around.

Invariant rules

1. Isolate before risk, don't revert after — a worktree replaces "run checkout -- . to undo"; the undo is worktree remove.
2. One worktree per parallel writer — never two agents mutating the same tree at once.
3. Don't nest — creating a worktree from inside a worktree; detect first.
4. Commit or isolate before delegating file-mutating work — a subagent must never be able to discard the main tree's unsaved changes.
5. Remove what you add — no orphaned worktrees; remove + prune when done.