mismatched-author checks a merge commit's identity at pre-merge-commit

[HackingGate]

A non-fast-forward git merge, and a git pull that merges, records a commit without running pre-commit; git runs pre-merge-commit instead. With mismatched-author at one stage, a merge under an identity passed in -c user.* or GIT_AUTHOR_* / GIT_COMMITTER_* was recorded unchecked.

• policy/base/mismatched-author.toml: [set] stages and the rule's git.hooks are ["pre-commit", "pre-merge-commit"]; the comment names both moments, and notes that a conflicted merge is concluded by git commit and was already covered.
• policy/base/sets.lock.json regenerated with cargo run --quiet -- rules --sets --json.
• docs/REFERENCE.md: the set's row says it installs pre-commit and pre-merge-commit.
• No engine change: the guard already parses the stage and dispatches the rule there.

Tests:

• tests/guard_cli.rs: uphold guard --stage pre-merge-commit refuses a bot identity in GIT_AUTHOR_* / GIT_COMMITTER_*, and passes the global one (and says the guard ran).
• tests/base_sets_cli.rs: a real git merge --no-ff through a pre-merge-commit hook in a repository inheriting the set is refused under a bot -c user.* and under bot GIT_* variables, with HEAD unchanged, and as the global identity records a two-parent commit. Both refusals fail against the one-stage set.
• every_guard_set_declares_the_stages_its_rules_install and tests/base_set_lock.rs pass.

A consumer that already lists uphold-guard-merge needs no policy change.

Closes #305

Summary by CodeRabbit

• New Features
  • The author-mismatch check now runs before both regular commits and merge commits, helping prevent merges with unexpected author or committer identities.
• Documentation
  • Updated the reference guide to reflect that the check applies to both commit stages.

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📥 Commits

Reviewing files that changed from the base of the PR and between e738762 and 09a667b.

📒 Files selected for processing (5)

• docs/REFERENCE.md
• policy/base/mismatched-author.toml
• policy/base/sets.lock.json
• tests/base_sets_cli.rs
• tests/guard_cli.rs

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⚙️ Run configuration

• Configuration used: defaults
• Review profile: CHILL
• Plan: Advanced
• Run ID: 0373a076-72d1-45ff-9347-bf64f3aa5582

📥 Commits

Reviewing files that changed from the base of the PR and between b1e8df3 and e738762.

📒 Files selected for processing (5)

• docs/REFERENCE.md
• policy/base/mismatched-author.toml
• policy/base/sets.lock.json
• tests/base_sets_cli.rs
• tests/guard_cli.rs

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📝 Walkthrough

Walkthrough

The mismatched-author set now checks author and committer identities at both pre-commit and pre-merge-commit. The documentation and lock file reflect the added stage. Integration tests cover matching and mismatching identities for direct guard runs and real merges.

Changes

Author identity checks

Layer / File(s)	Summary
Enable the merge-commit stage policy/base/mismatched-author.toml, policy/base/sets.lock.json, docs/REFERENCE.md	The set and rule now include pre-merge-commit alongside pre-commit. Comments and reference documentation describe both stages.
Verify guard behavior during merges tests/guard_cli.rs, tests/base_sets_cli.rs	Tests check that mismatching bot identities are refused and matching global identities pass. The merge tests also check that refused merges do not change HEAD and that successful merges create a two-parent commit.

Priority: ➖ Normal

Estimated code review effort: 3 (Moderate) | ~20 minutes

Change: Bug fix · Severity of issue fixed: Medium

Merge Risk: ⚪ Minimal · up to e7387

The merge-commit identity check has no identified merge-blocking issue. Run the reported tests as part of normal validation before merging.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Linked Issues check	✅ Passed	Issue #303 requires mismatched-author to check merge commits at pre-merge-commit, with no new engine path. The policy change adds that stage to both the set ceiling and rule hooks. The lock file a…
Out of Scope Changes check	✅ Passed	The policy, lock-file, documentation, and integration-test changes all support issue #303. No unrelated changes are identified in the whole-PR summary.
Docstring Coverage	✅ Passed	Docstring coverage is 92.31% which is sufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 13 functions across 2 files. (3 skipped: 3 …
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly identifies the main change: adding a pre-merge-commit identity check to the mismatched-author set.

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[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 94.10%. Comparing base (b1e8df3) to head (09a667b).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #304   +/-   ##
=======================================
  Coverage   94.10%   94.10%           
=======================================
  Files          46       46           
  Lines       21025    21025           
=======================================
  Hits        19786    19786           
  Misses       1239     1239           

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