Refuse AI-attribution lines in commit messages

.githooks/commit-msg

@@ -0,0 +1,9 @@
+#!/usr/bin/env bash
+# SPDX-License-Identifier: GPL-3.0-or-later
+# Copyright (C) 2026 Pau Aliagas <linuxnow@gmail.com>
+#
+# commit-msg: refuse a message that carries an AI-attribution line (tools/ai-trace-commit-check.sh;
+# the patterns are tools/ai-trace-patterns.json). Enable once per clone:
+#   git config core.hooksPath .githooks
+root=$(git rev-parse --show-toplevel) || exit 0
+exec "$root/tools/ai-trace-commit-check.sh" --msg-file "$1"

.github/workflows/ci.yml

@@ -89,3 +89,20 @@ jobs:
     with:
       publish: false
       arm: false  # aarch64/arm64 build at release only
+
+  # A commit message is published like a file. A pull request's own commits must carry no
+  # AI-attribution line (tools/ai-trace-commit-check.sh); what is already on the base is not read.
+  ai-trace:
+    name: commit messages carry no AI attribution
+    if: github.event_name == 'pull_request'
+    runs-on: ubuntu-latest
+    timeout-minutes: 5
+    steps:
+      - uses: actions/checkout@v4
+        with:
+          fetch-depth: 0
+          ref: ${{ github.event.pull_request.head.sha }}
+      - name: The checker catches a fixture and goes blind when its patterns are removed
+        run: tools/ai-trace-commit-check.sh --selftest
+      - name: Scan the commits of the pull request
+        run: tools/ai-trace-commit-check.sh origin/${{ github.event.pull_request.base.ref }}..HEAD

tools/ai-trace-commit-check.sh

@@ -0,0 +1,114 @@
+#!/bin/bash
+# SPDX-License-Identifier: GPL-3.0-or-later
+# Copyright (C) 2026 Pau Aliagas <linuxnow@gmail.com>
+#
+# ai-trace-commit-check.sh: fail when a commit message carries an AI-attribution line.
+#
+#   ai-trace-commit-check.sh <range>          every commit in the range (e.g. origin/main..HEAD)
+#   ai-trace-commit-check.sh --msg-file FILE  one message (the commit-msg hook; # lines are git comments, skipped)
+#   ai-trace-commit-check.sh --text-file FILE any text, every line judged (pull request titles and bodies)
+#   ai-trace-commit-check.sh --selftest       fixtures plus a sabotage run
+#
+# Exit 0 clean, 1 a hit (each commit and offending line is named), 2 a range, file or pattern list that cannot be read
+# (any crash is 2). A caller refuses on 2: a checker that cannot judge is never a pass.
+# The patterns are ai-trace-patterns.json beside this script; AI_TRACE_PATTERNS names another JSON (self-tests).
+set -euo pipefail
+export AI_TRACE_SELF="${BASH_SOURCE[0]}"
+exec python3 -I - "$@" <<'PY'
+import json, os, re, subprocess, sys
+
+here = os.path.dirname(os.path.realpath(os.environ["AI_TRACE_SELF"]))
+pfile = os.environ.get("AI_TRACE_PATTERNS") or os.path.join(here, "ai-trace-patterns.json")
+
+
+def load():
+    with open(pfile, encoding="utf-8") as f:
+        return [(m["name"], re.compile(m["pattern"], re.I | re.M)) for m in json.load(f)["markers"]]
+
+
+def hits(text, markers):
+    out = []
+    for n, line in enumerate(text.splitlines(), 1):
+        for name, rx in markers:
+            if rx.search(line):
+                out.append((n, name, line.strip()))
+    return out
+
+
+def report(label, text, markers):
+    h = hits(text, markers)
+    for n, name, line in h:
+        print(f"{label}: line {n} [{name}]: {line}")
+    return len(h)
+
+
+def git(*a):
+    p = subprocess.run(["git", *a], capture_output=True, text=True)
+    if p.returncode:
+        print(f"ai-trace-commit-check: git {' '.join(a[:3])}: {p.stderr.strip()}", file=sys.stderr)
+        sys.exit(2)
+    return p.stdout
+
+
+def selftest():
+    # built from fragments: this file must not itself carry an attribution line
+    co, by, ai = "Co-Authored-", "By: ", "Cl" + "aude"
+    sess = "Cl" + "aude-Session: https://cl" + "aude.ai/code/session_01"
+    fx = {
+        "co-authored-by": f"Fix x\n\n{co}{by}{ai} Opus <noreply@anthro" + "pic.com>\n",
+        "claude-session": f"Fix x\n\n{sess}\n",
+        "generated-footer": f"Fix x\n\n\U0001F916 Generated with [{ai} Code](https://{ai.lower()}.com/{ai.lower()}-code)\n",
+        "claude.ai/code": f"Fix x\n\nsee https://{ai.lower()}.ai/code/session_9\n",
+    }
+    clean = f"Fix x\n\nGenerated by the build; mentions a hidden directory and a {co}{by}Pau line.\n"
+    def run(markers):
+        bad = [k for k, v in fx.items() if not hits(v, markers)]
+        if hits(clean, markers):
+            bad.append("clean-flagged")
+        return bad
+    m = load()
+    first = run(m)
+    print("selftest:", "GREEN" if not first else f"RED {first}")
+    sab = run([x for x in m if x[0] not in ("co-authored-by", "ai-co-author", "anthropic-noreply", "claude-session")])
+    print("sabotage (the co-author, email and session patterns removed):", "RED as expected" if sab else "still GREEN: blind")
+    return 0 if not first and sab else 1
+
+
+def main(a):
+    if a == ["--selftest"]:
+        return selftest()
+    markers = load()
+    if len(a) == 2 and a[0] == "--msg-file":
+        try:
+            text = open(a[1], encoding="utf-8", errors="replace").read()
+        except OSError as e:
+            print(f"ai-trace-commit-check: {e}", file=sys.stderr)
+            return 2
+        # lines git adds as comments are not part of the message
+        text = "\n".join(l for l in text.splitlines() if not l.startswith("#"))
+        return 1 if report("commit message", text, markers) else 0
+    if len(a) == 2 and a[0] == "--text-file":
+        try:
+            text = open(a[1], encoding="utf-8", errors="replace").read()
+        except OSError as e:
+            print(f"ai-trace-commit-check: {e}", file=sys.stderr)
+            return 2
+        return 1 if report("text", text, markers) else 0
+    if len(a) == 1 and not a[0].startswith("-"):
+        shas = git("rev-list", a[0]).split()
+        bad = 0
+        for sha in shas:
+            bad += report(sha[:12], git("log", "-1", "--format=%B", sha), markers)
+        print(f"ai-trace-commit-check: {len(shas)} commits, {bad} offending lines")
+        return 1 if bad else 0
+    print(__doc__ if False else "usage: ai-trace-commit-check.sh <range> | --msg-file FILE | --text-file FILE | --selftest", file=sys.stderr)
+    return 2
+
+
+try:
+    rc = main(sys.argv[1:])
+except Exception as e:  # a bad or missing pattern file, a decode error: unreadable, never "a hit"
+    print(f"ai-trace-commit-check: {type(e).__name__}: {e}", file=sys.stderr)
+    rc = 2
+sys.exit(rc)
+PY

tools/ai-trace-patterns.json

@@ -0,0 +1,33 @@
+{
+ "$comment": "SPDX-License-Identifier: GPL-3.0-or-later. The AI-attribution patterns (Python re, flags IGNORECASE|MULTILINE) read by ai-trace-commit-check.sh. Edit here only.",
+ "markers": [
+  {
+   "name": "robot-footer",
+   "pattern": "^[^\\S\\r\\n]*[_*>]*[^\\S\\r\\n]*🤖[^\\r\\n]*?(?:Claude|claude\\.(?:ai|com))[^\\r\\n]*"
+  },
+  {
+   "name": "generated-footer",
+   "pattern": "(?:🤖[^\\S\\r\\n]*)?Generated[^\\S\\r\\n]+(?:with|by)[^\\S\\r\\n]+\\[?Claude[^\\S\\r\\n]+Code\\]?(?:\\([^)\\s]*\\))?"
+  },
+  {
+   "name": "co-authored-by",
+   "pattern": "Co-Authored-By:[^\\S\\r\\n]*Claude\\b[^\\r\\n<`]*(?:<[^>\\r\\n]*>)?"
+  },
+  {
+   "name": "ai-co-author",
+   "pattern": "Co-Authored-By:[^\\S\\r\\n]*(?:Anthropic|OpenAI|ChatGPT|Copilot|Gemini|Codex|Cursor|Aider|Devin)\\b[^\\r\\n<`]*(?:<[^>\\r\\n]*>)?"
+  },
+  {
+   "name": "anthropic-noreply",
+   "pattern": "noreply@anthropic\\.com"
+  },
+  {
+   "name": "claude-session",
+   "pattern": "Claude-Session:[^\\S\\r\\n]*[^\\s`]*"
+  },
+  {
+   "name": "claude.ai/code",
+   "pattern": "\\[[^\\]\\r\\n]*\\]\\([^\\S\\r\\n]*<?https?://claude\\.ai/code[^)\\s]*>?[^\\S\\r\\n]*\\)|<?https?://claude\\.ai/code\\b[^\\s)>`]*>?"
+  }
+ ]
+}