Isolate review subagents in throwaway git worktrees

[mattmenefee]

Summary

Every user-level subagent carries Edit and Write access, and a /local-review run puts several of them to work against one checkout at the same time. A reviewer that edits a file to test an assertion changes what its siblings are reading, and leaves changes in the working tree that nobody asked for. This adds the discipline that makes those grants safe, and fixes two harness defaults that would have quietly undermined it.

• home/.claude/CLAUDE.md gains a # Git Worktrees section holding the procedure once: how to isolate an agent, how to bootstrap a fresh checkout, what a worktree still shares with the real repository, and how to clean up. Custom subagents load the whole CLAUDE.md hierarchy (only the built-in Explore and Plan skip it), so one copy reaches every agent in every project
• All seven agents gain a short ## Working Alongside Other Agents section — advise rather than fix, verify only inside an isolated checkout, return the shared tree untouched
• All seven agents also gain EnterWorktree and ExitWorktree. Without these the instruction above would be unusable: an explicit tools: list is a whitelist, not an addition to the default pool, so the tool was not actually reachable
• worktree.baseRef is set to head. The default, fresh, branches an isolated agent from origin/<default branch> rather than the work under review — reviewers would have analyzed main while reporting on a feature branch, with nothing in their output to reveal it
• wt / wtl are hardened. git worktree list sorts linked worktrees by directory basename, so the harness's .claude/worktrees/agent-<id> checkouts sorted ahead of alice2–alice8 and renumbered them mid-session. Both now read through a wtlist helper that lists those entries last
• /doc-review gains a ## Reviewing Without Editing section: the only file the documentation-expert should write is the review, and accuracy checks that would modify the repository belong in a worktree
• .gitignore now covers /.claude/worktrees/, which was showing up as untracked

Test plan

• git worktree list ordering confirmed empirically in a throwaway repo: git sorts linked worktrees by basename, so agent-<id> landed at position 2 ahead of main2/main8
• With the wtlist helper, the same repo lists the agent worktree last, and wt 2 resolves to the second permanent worktree rather than the agent's
• zsh -n ~/.zshrc parses; wtl and wt 2 exercised end to end in a real zsh
• settings.json is valid JSON
• All 7 agent files parse as YAML frontmatter, with EnterWorktree and ExitWorktree present in every tools: list
• markdownlint clean on every changed Markdown file
• No new line exceeds 100 characters
• Not yet exercised: a full /local-review run with reviewers actually spawned under isolation: "worktree"

Requires source ~/.zshrc to pick up wtlist.