fix(setup): teach the update skill's drift check about the dispatcher hook flavour

[potiuk]

Summary

• setup-isolated-setup-update check 3 knows only one shape for the whole-user git hooks: ~/.claude/git-hooks/post-checkout as a copy of git-global-post-checkout.sh. Step P.3 of the install skill offers two flavours, and the dispatcher one installs git-hook-dispatcher.sh and symlinks every hook name to it — explicitly superseding the standalone post-checkout script.
• On a dispatcher install the check therefore diffs a symlink against a script it was never a copy of, and reports drift that is not there. Hit while running the skill against an install of that flavour.
• Both flavours are now named, with the source each diffs against, and the hook-name symlinks are called out as the installed shape rather than drift.

Type of change

• Skill change (.claude/skills/<name>/) — see test plan for why no eval fixture
• Tool / bridge contract (tools/<system>/*.md)
• Python package (tools/*/ with pyproject.toml)
• Groovy reference impl
• Cross-cutting (RFC, AGENTS.md, sandbox, privacy-LLM)
• Documentation (docs/, README.md, CONTRIBUTING.md)
• Project template (projects/_template/)
• CI / dev loop (prek, workflows, validators)

How it works

The whole-user-scope clause of check 3 splits by flavour, matching what Step P.3 / P.3b of setup-isolated-setup-install actually install: simple → a copy of git-global-post-checkout.sh at post-checkout; dispatcher → git-hook-dispatcher.sh plus a symlink per hook name. The instruction is now "diff whichever script is present against its own source", and the symlinks are stated to be the installed shape, so the false positive cannot be reported as drift.

docs/mode-economics.md moves because the skill-token-count hook remeasures the skill.

Test plan

• prek run --all-files passes (32 hooks, exit 0).
• Checked against a real dispatcher-flavour install: global core.hooksPath = ~/.claude/git-hooks, all 11 hook names symlinked to git-hook-dispatcher.sh, which is byte-identical to tools/agent-isolation/git-hook-dispatcher.sh. Under the old text that install reads as drift; under the new text it reads as clean.
• No eval fixture added. This is a read-and-report instruction, not a classification boundary, and none of the skill's four eval suites extracts check 3. The change is prose-only.

RFC-AI-0004 compliance

• Conversational + correctable — the skill stays read-only and proposal-only; only the reported verdict changes.

Linked issues

None.

Notes for reviewers (optional)

• The same clause still assumes the operator installed one of the two flavours. A host that somehow has both (a leftover post-checkout copy beside the dispatcher) is not described — I left that out rather than guess, since the install skill says the dispatcher supersedes the copy.

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