feat(claude): stale-worktree-cleaner skill (foxhunt)

Classifies worktrees (NO-COMMITS / GONE / MERGED / UNCOMMITTED / ACTIVE) and
proposes cleanup. User confirms each removal individually; never --force,
never -D. Composes commit-commands:clean_gone where applicable.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

.claude/skills/foxhunt/stale-worktree-cleaner/SKILL.md

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+---
+name: stale-worktree-cleaner
+description: Identifies stale git worktrees in .claude/worktrees/ and the workspace, including [gone] tracking refs and merged branches. Produces a per-worktree cleanup plan; user confirms each git worktree remove individually before any destructive operation.
+---
+
+# Foxhunt Stale Worktree Cleaner
+
+Destructive op — explicit invoke only, with per-action user confirmation.
+
+## When to invoke
+
+- "Clean stale worktrees".
+- Periodically when `.claude/worktrees/` has many entries.
+
+## What this skill does
+
+1. **Enumerate** all worktrees:
+   ```bash
+   git worktree list
+   ls -la .claude/worktrees/
+   ```
+
+2. **For each worktree**, classify staleness:
+
+   | Class | Detection |
+   |---|---|
+   | NO-COMMITS | No commits in N days (default 30); branch unchanged |
+   | GONE | Tracking ref `[gone]` (deleted upstream) — `git fetch -p` then `git branch -vv` |
+   | MERGED | Branch fully merged into `main` (`git merge-base --is-ancestor`) |
+   | UNCOMMITTED | Has uncommitted changes — DO NOT propose cleanup; flag only |
+   | ACTIVE | Recent commits, not merged, tracking ref alive |
+
+3. **Produce a per-worktree cleanup plan**:
+
+   ```
+   [stale-worktree-cleaner] enumerated <N> worktrees
+
+   Class NO-COMMITS (<K> entries):
+   1. <path> — branch <name>, last commit <date>, status <merged|alive>
+      Action: git worktree remove <path>; git branch -d <name>
+
+   Class GONE (<K> entries):
+   ...
+
+   Class UNCOMMITTED (<K> entries — flag only, no action proposed):
+   ...
+   ```
+
+4. **Confirm each action individually** before running. Never bulk-execute.
+
+## Discipline
+
+- **NEVER `git worktree remove --force` without confirmation.** `--force` discards uncommitted work.
+- **NEVER `git branch -D`** (force delete) — only `git branch -d` (allows refusal on unmerged).
+- **Compose the existing `commit-commands:clean_gone` skill** when applicable (it handles GONE-class branches).
+- **NetBird/Tailscale/CI worktrees** (if any) — leave alone unless explicitly named by the user.
+- **Worktrees referenced by a running agent** must not be removed. Check `.claude/worktrees/*` against any active session metadata.
+
+## Output format
+
+```
+[stale-worktree-cleaner] proposal:
+
+Will remove (after your per-item confirmation):
+- <path 1> [<class>] — <why>
+- <path 2> [<class>] — <why>
+
+Skipped (require manual review):
+- <path 3> [UNCOMMITTED] — has unstaged changes
+```
+
+User confirms each removal individually before any destructive command runs.