test(hooks): characterize the six remaining guard hooks

[MANVENDRA-github]

Why

Before #30, no test in this repo had ever executed a hook. The suite covered the transform layer only. That is precisely how protect-generated-dirs spent three minor versions guarding the wrong set of directories without anyone noticing.

#30 tested the one hook with a defect. This tests the other six, so a later edit to a regex or a pathspec parser cannot silently widen or narrow a guard.

What is pinned

Hook	Blocks	Deliberately allows
block-no-verify	--no-verify, -n, --no-gpg-sign, -c commit.gpgsign=false	echo --no-verify (not a git call)
block-force-push	main/master, incl. --force-with-lease	force-pushing a feature branch
guard-dangerous-bash	/, /*, ~, $HOME, chmod -R 777 /, curl | sh, dd of=/dev/sd*, mkfs, fork bomb	sudo rm -rf /var, rm -rf ./build, git reset --hard
protect-lockfile-edit	12 ecosystems' lockfiles	package.json, source files
secret-scan-on-edit	AWS key id, GitHub PAT, private-key header; reads new_string and content	process.env.API_KEY, a placeholder in .env.example
block-secret-file-stage	git add .env, the sweeping git add . / -A	--dry-run, .env.example, a gitignored file

Two of those "allows" deserve saying out loud rather than treating as bugs:

• guard-dangerous-bash does not block sudo rm -rf /var. Its header calls the list "intentionally narrow: unambiguously dangerous shapes, not commands that touch files." rm -rf /var is routine inside a container. Widening the list is a design change, not a bug fix — the test now documents that boundary instead of leaving the next reader to guess.
• block-force-push permits force-pushing a feature branch. That's the author's own history to rewrite.

block-secret-file-stage resolves pathspecs by asking git itself, so testing it against a fake payload only tests the parser. It's exercised against a real temporary git repository holding a real .env and server.key.

Fail-open is the contract

Every hook is asserted to exit 0 on empty stdin, malformed JSON, {}, a missing tool_input, and a null command/file_path. A hook that throws returns non-zero — which blocks every tool call in the session. Failing open is the contract, not an accident. That's 42 of the assertions here.

These tests are not tautological

Mutation-checked. Flip one process.exit(2) to exit(0) in block-force-push:

$ npm test
# pass 236
# fail 3        <- exactly the three force-push block cases

$ git checkout hooks/block-force-push.js && npm test
# pass 239
# fail 0

Verification

$ npm test
# tests 239     (was 143, was 98 before #30)
# suites 12
# pass 239
# fail 0

$ npm run lint    # PASS
$ npm run sync    # clean, no drift

All seven hooks now have coverage. Only README.md and the new test file change — no source or generated output touched.