Check the Shared Hook Before Installing and Deny a Commit-Time hooksPath Override

[ptr727]

Summary

Refs #1816.

• repo-worktree "Preparing Git Hooks". A linked worktree shares the base clone's git config, and with no core.hooksPath set it also shares the base clone's hooks directory. Running pre-commit install there rewrote the hook for every checkout. The section now:
  • checks for an existing hook with git rev-parse --git-path hooks before installing;
  • identifies a linked worktree by --git-dir differing from --git-common-dir, both run from the root;
  • forbids changing a shared hook or setting from a linked worktree, and binds a repository override to the same limit;
  • lets a standalone clone install into its own hooks;
  • runs the Husky.Net install in a linked worktree only where core.hooksPath already reads .husky;
  • names a commit-time core.hooksPath override as a hook bypass.
• gh-write-guard denies git -c core.hooksPath=... commit|push and the --config-env forms beside --no-verify, with self-test rows. It refactors _git_subcommand_arglists onto a new _git_subcommand_invocations that keeps the global options.
• Guard READMEs name the new denial.

The remaining bypass routes, all older than this change, are filed as #2177: a persistent git config core.hooksPath, the GIT_CONFIG_* environment forms, wrapped or aliased git, and a heredoc false positive.

Verification

• gh-write-guard.py --selftest passes. With the new check disabled, the four new deny rows fail.
• Hook-path resolution was probed in a scratch base clone and linked worktree, with and without a relative core.hooksPath.
• Four local strict-review passes ran, raising 7, 2, 1, and 0 findings. The last pass is clean at the pushed head.

🤖 Generated with Claude Code

[coderabbitai]

Important

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 56.47%. Comparing base (3196954) to head (e61345f).

Additional details and impacted files

@@           Coverage Diff            @@
##           develop    #2178   +/-   ##
========================================
  Coverage    56.47%   56.47%           
========================================
  Files           16       16           
  Lines         7455     7455           
========================================
  Hits          4210     4210           
  Misses        3245     3245           

Flag	Coverage Δ
python-3.13	56.47% <ø> (ø)

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[Copilot]

Copilot review overview

🔵 Needs a closer look

It changes a security bypass-prevention gate and fleet-wide carried governance content, which the repository treats as design-level and durable-when-wrong, so it warrants final human sign-off despite passing all verification.

Review effort: Balanced
Findings: None

What changed in this PR

This PR closes a hook-safety gap surfaced by the linked issue: running a hook installer (pre-commit/prek/Husky.Net) from a linked worktree rewrote the hook that every checkout of the base clone shares, and a commit-time core.hooksPath override could silently skip hooks the way --no-verify does. It hardens the repo-worktree skill guidance and extends the gh-write-guard PreToolUse hook to deny the per-invocation core.hooksPath override, fitting into the fleet's agent-safety guardrail layer.

Changes:

• repo-worktree "Preparing Git Hooks" now checks for an existing shared hook before installing, distinguishes linked worktrees (--git-dir vs --git-common-dir) from standalone clones, forbids changing a shared hook/setting from a linked worktree, and names a commit-time core.hooksPath override as a bypass.
• gh-write-guard.py denies git -c core.hooksPath=... commit|push and both --config-env forms, via a new _overrides_hooks_path helper and a _git_subcommand_invocations refactor that preserves _git_subcommand_arglists; eight self-test rows cover the new positive and negative cases.
• Guard READMEs document the new denial, and the generated skill copies plus their source digest are regenerated in sync.

File	Description
host-setup/​agent-safety/​claude/​gh-write-guard.py	Adds _overrides_hooks_path + _git_subcommand_invocations, wires the new deny into _check_bypass_flags, and adds self-test rows. Verified correct via direct execution and passing --selftest.
.agents/​skills/​repo-worktree/​SKILL.md	Source-of-truth prose: shared-hook check, linked-worktree prohibition, commit-time override as bypass.
.github/​skills/​repo-worktree/​SKILL.md	Generated copy, byte-identical to source (do not edit directly).
.claude-plugin/​fleet-skills/​skills/​repo-worktree/​SKILL.md	Generated copy, byte-identical to source.
.claude-plugin/​fleet-skills/​.source-digests/​repo-worktree	Regenerated digest; reproduces exactly via build_dist.skill_digest.
host-setup/​agent-safety/​README.md	Requirement-4 prose extended to name the -c core.hooksPath= denial.
host-setup/​agent-safety/​claude/​README.md	Guard bullet extended to name the core.hooksPath override denial.

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