fix(hooks): move the merge-signature gate off prepare-commit-msg

git commit --no-verify skips pre-commit and commit-msg, but not prepare-commit-msg. The gate sat on that stage, so the pre-commit framework ran on every commit regardless and did its stash-unstaged dance. Inside the agent sandbox its rollback (git checkout -- .) cannot unlink the bind-mounted .claude/settings.json, aborts mid-restore, and leaves every unstaged change reverted to HEAD -- twelve files of work, no commit created.

The gate itself is harmless: merge_signed.sh returns 0 immediately without a MERGE_HEAD. Only the stage was wrong. On commit-msg it still runs for a normal merge commit, and --no-verify now behaves as documented. Tradeoff: a merge committed with --no-verify skips the signature check, same as it already skips make test.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

.pre-commit-config.yaml

@@ -1,7 +1,7 @@
 ---
 default_install_hook_types:
   - pre-commit
-  - prepare-commit-msg
+  - commit-msg
   - pre-push
   - post-checkout
 
@@ -22,7 +22,7 @@ repos:
         pass_filenames: false
         always_run: true
         stages:
-          - prepare-commit-msg
+          - commit-msg
       - id: make-lint
         name: Run make lint (pre-push gate)
         entry: make lint

Makefile

@@ -745,7 +745,7 @@ test-main-merged:
 	@bash scripts/git/assert/main_merged.sh
 
 .PHONY: test-merge-signed
-# Verify every commit an in-progress merge brings in (HEAD..MERGE_HEAD) is signed (prepare-commit-msg gate).
+# Verify every commit an in-progress merge brings in (HEAD..MERGE_HEAD) is signed (commit-msg gate).
 test-merge-signed:
 	@bash scripts/git/assert/merge_signed.sh