fix(git-guards): enforce kernel coding-assistants trailer spec

git-guards/scripts/commit-trailer-guard.py

@@ -1,19 +1,31 @@
 #!/usr/bin/env python3
 """
-commit-trailer-guard.py - PreToolUse hook to rewrite Assisted-by trailer to kernel spec.
+commit-trailer-guard.py - PreToolUse hook to enforce kernel coding-assistants spec.
 
-Detects `Assisted-by: Claude <...>` in git commit commands and rewrites to
-`Assisted-by: Claude:<model>` per https://docs.kernel.org/process/coding-assistants.html.
+Per https://docs.kernel.org/process/coding-assistants.html:
+  Correct:   Assisted-by: Claude:claude-opus-4-7
+  Wrong:     Assisted-by: Claude <noreply@anthropic.com>  (email form)
+  Wrong:     Assisted-by: Claude                          (bare, no model)
+  Stripped:  🤖 Generated with [Claude Code](...)         (not part of spec)
 """
 
 import json
 import re
 import sys
 from pathlib import Path
 
-TRAILER_PATTERN = re.compile(r"Assisted-by:\s*Claude\s*<[^>]*>")
+# Matches the email form and the bare form, but NOT the already-correct Agent:model form.
+# \b after Claude prevents false matches on names like "Claudette", "Claudine", etc.
+TRAILER_PATTERN = re.compile(r"Assisted-by:\s*Claude\b(?:\s*<[^>]*>|(?!\s*:\S))")
 TRAILER_REPL = "Assisted-by: Claude:{model}"
 
+_ROBOT_URL_PATTERN = r"🤖 Generated with \[Claude Code\]\([^)]*\)"
+# When the robot line is preceded by a blank line, replace the pair with a single newline
+# so the text before it still ends cleanly (e.g. heredoc EOF stays on its own line).
+_ROBOT_DOUBLE_NL = re.compile(r"\n\n" + _ROBOT_URL_PATTERN + r"\n?")
+# When the robot line has no preceding blank, remove it entirely.
+_ROBOT_SINGLE = re.compile(r"(?:\n|^)" + _ROBOT_URL_PATTERN + r"\n?")
+
 # Matches git global flags that take a value (-C/-c) to strip before subcommand detection.
 _GIT_GLOBAL_VALUE = re.compile(r'^-[Cc]\s+(?:"[^"]*"|\'[^\']*\'|\S+)\s*')
 # Matches valueless git global flags (-p/-P/--paginate/etc.).
@@ -79,28 +91,43 @@ def main() -> None:
     tool_input = data.get("tool_input", {})
     command = tool_input.get("command", "")
 
-    if not TRAILER_PATTERN.search(command):
-        sys.exit(0)
+    is_commit = command.startswith("git ") and _is_git_commit(command)
+    needs_trailer_fix = is_commit and bool(TRAILER_PATTERN.search(command))
+    needs_robot_strip = bool(_ROBOT_DOUBLE_NL.search(command) or _ROBOT_SINGLE.search(command))
 
-    if not command.startswith("git ") or not _is_git_commit(command):
+    if not needs_trailer_fix and not needs_robot_strip:
         sys.exit(0)
 
-    model = _get_model_from_transcript(data.get("transcript_path", ""))
-    if not model:
-        sys.exit(0)
+    model = ""
+    if needs_trailer_fix:
+        model = _get_model_from_transcript(data.get("transcript_path", ""))
+        if not model:
+            needs_trailer_fix = False
+
+    new_command = command
+    if needs_robot_strip:
+        new_command = _ROBOT_DOUBLE_NL.sub("\n", new_command)
+        new_command = _ROBOT_SINGLE.sub("", new_command)
+    if needs_trailer_fix:
+        new_command = TRAILER_PATTERN.sub(TRAILER_REPL.format(model=model), new_command)
 
-    new_command = TRAILER_PATTERN.sub(TRAILER_REPL.format(model=model), command)
     if new_command == command:
         sys.exit(0)
 
+    reason_parts = []
+    if needs_trailer_fix:
+        reason_parts.append(f"trailer rewritten (model={model})")
+    if needs_robot_strip:
+        reason_parts.append("robot-signature line stripped")
+
     print(json.dumps({
         "hookSpecificOutput": {
             "hookEventName": "PreToolUse",
             "permissionDecision": "allow",
             "permissionDecisionReason": (
-                f"Trailer rewritten to kernel coding-assistants spec "
+                "kernel coding-assistants spec enforced "
                 f"(https://docs.kernel.org/process/coding-assistants.html): "
-                f"model={model}"
+                + ", ".join(reason_parts)
             ),
         },
         "updatedInput": {**tool_input, "command": new_command},

git-guards/scripts/test_commit_trailer_guard.py

@@ -16,7 +16,9 @@
 
 MODEL = "claude-opus-4-7"
 OLD_TRAILER = "Assisted-by: Claude <noreply@anthropic.com>"
+BARE_TRAILER = "Assisted-by: Claude"
 NEW_TRAILER = f"Assisted-by: Claude:{MODEL}"
+ROBOT_LINE = "🤖 Generated with [Claude Code](https://claude.com/claude-code)"
 
 
 def _make_transcript(model: str = MODEL) -> str:
@@ -133,6 +135,81 @@ def check(label: str, command: str, expected_decision: str,
     transcript_path=transcript,
 )
 
+# 8. Bare trailer (no email, no model) → rewritten to Agent:model
+cmd8 = f'git commit -m "fix: x\n\n{BARE_TRAILER}"'
+all_pass &= check(
+    "bare trailer rewrite",
+    cmd8,
+    "allow",
+    transcript_path=transcript,
+    expected_new_command=cmd8.replace(BARE_TRAILER, NEW_TRAILER),
+)
+
+# 9. Robot line preceded by blank in commit (already-correct trailer) → robot stripped.
+#    The blank-line replacement (\n\n🤖... → \n) leaves a trailing \n inside the message.
+cmd9 = f'git commit -m "fix: x\n\n{NEW_TRAILER}\n\n{ROBOT_LINE}"'
+expected9 = f'git commit -m "fix: x\n\n{NEW_TRAILER}\n"'
+all_pass &= check(
+    "robot line stripped from commit",
+    cmd9,
+    "allow",
+    transcript_path=transcript,
+    expected_new_command=expected9,
+)
+
+# 10. Robot line in gh pr create body → stripped (not a git command).
+#    \n\n🤖...\n → \n keeps the heredoc EOF on its own line.
+pr_cmd = (
+    f'gh pr create --title "feat: x" --body "$(cat <<\'EOF\'\n'
+    f'## Summary\n- did a thing\n\n'
+    f'{ROBOT_LINE}\n'
+    f'EOF\n)"'
+)
+expected10 = (
+    f'gh pr create --title "feat: x" --body "$(cat <<\'EOF\'\n'
+    f'## Summary\n- did a thing\n'
+    f'EOF\n)"'
+)
+all_pass &= check(
+    "robot line stripped from gh pr create",
+    pr_cmd,
+    "allow",
+    transcript_path=transcript,
+    expected_new_command=expected10,
+)
+
+# 11. Bare trailer + robot line together → both fixed in one pass.
+#    Robot strip runs first, leaving trailing \n; then trailer fix rewrites BARE → NEW.
+cmd11 = f'git commit -m "fix\n\n{BARE_TRAILER}\n\n{ROBOT_LINE}"'
+expected11 = f'git commit -m "fix\n\n{NEW_TRAILER}\n"'
+all_pass &= check(
+    "bare trailer + robot line fixed together",
+    cmd11,
+    "allow",
+    transcript_path=transcript,
+    expected_new_command=expected11,
+)
+
+# 12. Robot line + missing transcript → robot still stripped (robot strip is transcript-independent).
+cmd12 = f'git commit -m "fix: x\n\n{ROBOT_LINE}"'
+expected12 = 'git commit -m "fix: x\n"'
+all_pass &= check(
+    "robot line stripped even without transcript",
+    cmd12,
+    "allow",
+    transcript_path="",
+    expected_new_command=expected12,
+)
+
+# 13. Name that starts with "Claude" (Claudette) must NOT be rewritten — word-boundary guard.
+cmd13 = 'git commit -m "fix: x\n\nAssisted-by: Claudette <claudette@example.com>"'
+all_pass &= check(
+    "name starting with Claude is not rewritten",
+    cmd13,
+    "silent_allow",
+    transcript_path=transcript,
+)
+
 print()
 print("ALL TESTS PASSED" if all_pass else "SOME TESTS FAILED")
 sys.exit(0 if all_pass else 1)