Add a commit-msg hook for this project's attribution form

card-games is published, so its commit messages are permanent public
record.  The new hook refuses a session-link trailer and a
Co-Authored-By trailer naming Claude or anthropic.com, and checks that
any Assisted-by trailer reads NAME (for PERSON; MODEL).  A message with
no Assisted-by line passes: attribution stays the author's call.

* hooks/commit-msg: New hook.
* hooks/applypatch-msg: New hook; runs commit-msg for git am.
* test/commit-msg-tests.el: New ERT tests that drive the sh hook.
* Makefile (GITHOOKS): New variable.
(hooks): Install all three hooks.
(test-hooks): New target.
(check): Run it.

Assisted-by: Mentat (for Corwin; claude-opus-5-5)

Makefile

@@ -21,7 +21,7 @@ README   = README.md
 EXTRA    = README.org $(README) $(PKGDESC) $(MANUAL) $(VERTEXI) $(IMAGES)
 
 .PHONY: all compile test clean distclean checkdoc lint check package tarball elpa release help \
-        info info-emacs html pdf docclean version readme hooks
+        info info-emacs html pdf docclean version readme hooks test-hooks
 
 help:
 	@echo "card-games $(VERSION) -- make targets:"
@@ -32,7 +32,8 @@ help:
 	@echo "  check      compile + checkdoc + lint + test (the full gate)"
 	@echo "  version    regenerate $(VERTEXI) from VERSION"
 	@echo "  readme     export README.org -> README.md (Emacs batch)"
-	@echo "  hooks      install the git pre-commit hook"
+	@echo "  hooks      install the git hooks (pre-commit, commit-msg, applypatch-msg)"
+	@echo "  test-hooks test the commit-msg hook"
 	@echo "  info       build the Info manual ($(INFO)) with makeinfo"
 	@echo "  info-emacs build the Info manual with Emacs alone (fallback)"
 	@echo "  html       build the one-file HTML manual"
@@ -51,9 +52,13 @@ compile:
 test:
 	$(BATCH) -L test -l test/$(PKG)-tests.el -f ert-run-tests-batch-and-exit
 
+# The commit-msg hook is sh; its tests are ERT, so each checks the other.
+test-hooks:
+	$(EMACS) -Q --batch -l test/commit-msg-tests.el -f ert-run-tests-batch-and-exit
+
 # One gate a contributor (or CI) can run: the same quality tools MELPA
 # asks for -- byte-compile, checkdoc, package-lint -- plus the ERT suite.
-check: compile checkdoc lint test
+check: compile checkdoc lint test test-hooks
 	@echo "card-games $(VERSION): compile + checkdoc + lint + tests all green"
 
 checkdoc:
@@ -111,12 +116,15 @@ readme: $(README)
 $(README): README.org build.el
 	$(BATCH) -l build.el
 
-# Install the pre-commit hook into this checkout's .git/hooks.
+# Install the git hooks into this checkout's .git/hooks.
+GITHOOKS = pre-commit commit-msg applypatch-msg
 hooks:
 	@if [ -d .git ]; then \
-	  cp hooks/pre-commit .git/hooks/pre-commit && \
+	  for h in $(GITHOOKS); do \
-	  chmod +x .git/hooks/pre-commit && \
+	    cp hooks/$$h .git/hooks/$$h && \
-	  echo "Installed .git/hooks/pre-commit"; \
+	    chmod +x .git/hooks/$$h && \
+	    echo "Installed .git/hooks/$$h" || exit 1; \
+	  done; \
 	else \
 	  echo "No .git directory here; skipping hook install."; \
 	fi

hooks/applypatch-msg

@@ -0,0 +1,11 @@
+#!/bin/sh
+# hooks/applypatch-msg -- give patches applied with `git am' the same
+# trailer check as an ordinary commit, by running hooks/commit-msg.
+#
+# Install:  make hooks
+
+hook=$(git rev-parse --git-path hooks/commit-msg)
+if [ -x "$hook" ]; then
+    exec "$hook" "$@"
+fi
+exit 0

hooks/commit-msg

@@ -0,0 +1,59 @@
+#!/bin/sh
+# hooks/commit-msg -- keep commit trailers in this project's attribution form.
+#
+# card-games is published (MELPA, and bound for GNU ELPA), so every commit
+# message is a permanent public record.  This hook refuses two trailers the
+# project has not agreed to and checks the one form it has:
+#
+#   refused  a session-link trailer (Claude-Session and the like)
+#   refused  Co-Authored-By naming Claude or anthropic.com
+#   checked  Assisted-by: NAME (for PERSON; MODEL)
+#            e.g.  Assisted-by: Mentat (for Corwin; claude-opus-5-5)
+#            A comma in place of the semicolon is accepted too.
+#
+# Attribution is the author's call: a message with no Assisted-by line
+# passes.  Comment lines, and everything after the scissors line that
+# `git commit -v' adds, are not checked.
+#
+# Install:  make hooks  (also installs applypatch-msg, so `git am' is checked)
+# Bypass:   git commit --no-verify  -- a hook is a check, not a lock.
+# Tests:    make test-hooks
+#
+# Usage: commit-msg MESSAGE-FILE    Exit 0 accepts, 1 refuses.
+
+set -u
+
+msg=${1:?usage: commit-msg MESSAGE-FILE}
+cr=$(printf '\r')
+status=0
+
+refuse () {
+    printf 'commit-msg: %s\n    %s\n' "$1" "$2" >&2
+    status=1
+}
+
+while IFS= read -r line || [ -n "$line" ]; do
+    line=${line%"$cr"}
+    case $line in
+        '# ------------------------ >8 ------------------------'*) break ;;
+        '#'*) continue ;;
+    esac
+    lower=$(printf '%s' "$line" | tr '[:upper:]' '[:lower:]')
+    case $lower in
+        claude-session:*)
+            refuse 'session links are not used in this project:' "$line" ;;
+        co-authored-by:*claude*|co-authored-by:*anthropic.com*)
+            refuse 'credit AI help as Assisted-by: NAME (for PERSON; MODEL), not:' "$line" ;;
+        assisted-by:*)
+            if ! printf '%s\n' "$line" |
+                 grep -Eq '^[Aa]ssisted-[Bb]y: [^ (][^(]* \(for [^;,()]+[;,] [^ ;,()]+\)$'
+            then
+                refuse 'expected Assisted-by: NAME (for PERSON; MODEL), got:' "$line"
+            fi ;;
+    esac
+done < "$msg"
+
+if [ "$status" -ne 0 ]; then
+    echo 'commit-msg: refused; fix the message and try again.' >&2
+fi
+exit "$status"

test/commit-msg-tests.el

@@ -0,0 +1,76 @@
+;;; commit-msg-tests.el --- ERT tests for hooks/commit-msg  -*- lexical-binding: t; -*-
+
+;; Run with:  make test-hooks   (or)
+;;   emacs -Q --batch -l test/commit-msg-tests.el -f ert-run-tests-batch-and-exit
+;;
+;; The hook is POSIX sh; these tests drive it from Emacs Lisp, so the
+;; check and its tests are written in different languages.  Each test
+;; feeds one message file to the hook and reads only its exit status.
+;; The table holds messages that must pass and messages that must be
+;; refused, so a hook that accepts everything, or refuses everything,
+;; fails here.
+
+;;; Code:
+
+(require 'ert)
+
+(defconst cmt--hook
+  (expand-file-name "../hooks/commit-msg"
+                    (file-name-directory (or load-file-name buffer-file-name)))
+  "The hook under test.")
+
+(defun cmt--status (message)
+  "Return the exit status of the hook run on MESSAGE."
+  (let ((file (make-temp-file "commit-msg-test-")))
+    (unwind-protect
+        (progn
+          (let ((coding-system-for-write 'no-conversion))
+            (with-temp-file file (insert message)))
+          (call-process "sh" nil nil nil cmt--hook file))
+      (delete-file file))))
+
+(defconst cmt--subject "Fix a thing\n\nBody text.\n\n")
+
+(defconst cmt--accept
+  `(("no trailer at all"        . "Fix a thing\n\nBody text.\n")
+    ("persona form, semicolon"  . ,(concat cmt--subject "Assisted-by: Mentat (for Corwin; claude-opus-5-5)\n"))
+    ("persona form, comma"      . ,(concat cmt--subject "Assisted-by: Mentat (for Corwin, claude-opus-5-5)\n"))
+    ("key case varies"          . ,(concat cmt--subject "Assisted-By: Mentat (for Corwin; claude-opus-5-5)\n"))
+    ("CRLF line endings"        . "Fix a thing\r\n\r\nAssisted-by: Mentat (for Corwin; claude-opus-5-5)\r\n")
+    ("no final newline"         . ,(concat cmt--subject "Assisted-by: Mentat (for Corwin; claude-opus-5-5)"))
+    ("comment line ignored"     . ,(concat cmt--subject "# Claude-Session: https://example.invalid/x\n"))
+    ("after the scissors line"  . ,(concat cmt--subject
+                                           "# ------------------------ >8 ------------------------\n"
+                                           "+Claude-Session: https://example.invalid/x\n"
+                                           "+Co-Authored-By: Claude <noreply@anthropic.com>\n")))
+  "Messages the hook must accept, by name.")
+
+(defconst cmt--refuse
+  `(("session link"             . ,(concat cmt--subject "Claude-Session: https://claude.ai/code/session_x\n"))
+    ("session link, lower case" . ,(concat cmt--subject "claude-session: https://claude.ai/code/session_x\n"))
+    ("co-author, Claude"        . ,(concat cmt--subject "Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>\n"))
+    ("co-author, lower case"    . ,(concat cmt--subject "co-authored-by: Someone <bot@anthropic.com>\n"))
+    ("older Assisted-by form"   . ,(concat cmt--subject "Assisted-by: Claude:claude-opus-4-8\n"))
+    ("persona form, no model"   . ,(concat cmt--subject "Assisted-by: Mentat (for Corwin)\n"))
+    ("persona form, no person"  . ,(concat cmt--subject "Assisted-by: Mentat (claude-opus-5-5)\n"))
+    ("good line then a bad one" . ,(concat cmt--subject
+                                           "Assisted-by: Mentat (for Corwin; claude-opus-5-5)\n"
+                                           "Claude-Session: https://claude.ai/code/session_x\n")))
+  "Messages the hook must refuse, by name.")
+
+(ert-deftest cmt-accepts ()
+  "Every message in `cmt--accept' passes the hook."
+  (skip-unless (executable-find "sh"))
+  (dolist (case cmt--accept)
+    (should (equal (cons (car case) 0)
+                   (cons (car case) (cmt--status (cdr case)))))))
+
+(ert-deftest cmt-refuses ()
+  "Every message in `cmt--refuse' is refused by the hook."
+  (skip-unless (executable-find "sh"))
+  (dolist (case cmt--refuse)
+    (should (equal (cons (car case) 1)
+                   (cons (car case) (cmt--status (cdr case)))))))
+
+(provide 'commit-msg-tests)
+;;; commit-msg-tests.el ends here