From 208a079f4230edd520f5aa92288ae48247340910 Mon Sep 17 00:00:00 2001
From: Craig Jennings <c@cjennings.net>
Date: Sun, 19 Apr 2026 17:14:54 -0500
Subject: feat(hooks): shared _common.py helpers + systemMessage AI-attribution
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Consolidates stdin-parse and response-emit across the two confirm hooks
into `hooks/_common.py` (stdlib-only, sibling symlinked alongside the
hooks it serves). Net ~28 lines less duplication.

Adds a `systemMessage` banner alongside the confirmation modal when the
commit message or PR title/body contains AI-attribution patterns:

  - Co-Authored-By: Claude|Anthropic|GPT|AI trailers
  - 🤖 robot emoji
  - "Generated with Claude Code" / similar footers
  - "Created with …" / "Assisted by …" variants

Scanning targets structural leak patterns only — bare mentions of
"Claude" or "Anthropic" in diff context don't fire, so discussing the
tools themselves in a commit message doesn't false-positive.

Clean-room synthesis from GowayLee/cchooks (MIT) — specifically, the
systemMessage-alongside-reason pattern and event-aware stdin helpers.
---
 hooks/_common.py | 75 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 75 insertions(+)
 create mode 100644 hooks/_common.py

(limited to 'hooks/_common.py')

diff --git a/hooks/_common.py b/hooks/_common.py
new file mode 100644
index 0000000..d4bf520
--- /dev/null
+++ b/hooks/_common.py
@@ -0,0 +1,75 @@
+"""Shared helpers for Claude Code PreToolUse confirmation hooks.
+
+Not a hook itself — imported by sibling scripts in ~/.claude/hooks/
+(installed as symlinks by `make install-hooks`). Python resolves imports
+relative to the invoked script's directory, so sibling symlinks just work.
+
+Provides:
+  read_payload()      → dict parsed from stdin (empty dict on failure)
+  respond_ask(...)    → emit a PreToolUse permissionDecision=ask response
+  scan_attribution()  → detect AI-attribution patterns in commit/PR text
+
+AI-attribution scanning targets structural leak patterns (trailers,
+footers, robot emoji) — NOT bare mentions of 'Claude' or 'Anthropic',
+which are legitimate words and would false-positive on diffs discussing
+the tools themselves.
+"""
+
+import json
+import re
+import sys
+from typing import Optional
+
+
+ATTRIBUTION_PATTERNS: list[tuple[str, str]] = [
+    (r"Co-Authored-By:\s*(?:Claude|Anthropic|GPT|AI\b|an? LLM)",
+     "Co-Authored-By trailer crediting an AI"),
+    (r"🤖",
+     "robot emoji (🤖)"),
+    (r"Generated (?:with|by) (?:Claude|Anthropic|AI|an? LLM)",
+     "'Generated with AI' footer"),
+    (r"Created (?:with|by) (?:Claude|Anthropic|AI|an? LLM)",
+     "'Created with AI' footer"),
+    (r"Assisted by (?:Claude|Anthropic|AI|an? LLM)",
+     "'Assisted by AI' credit"),
+    (r"\[\s*(?:Claude|AI|LLM)\s*(?:Code)?\s*\]",
+     "[Claude] / [AI] bracketed tag"),
+]
+
+
+def read_payload() -> dict:
+    """Parse tool-call JSON from stdin. Return {} on any parse failure."""
+    try:
+        return json.loads(sys.stdin.read())
+    except (json.JSONDecodeError, ValueError):
+        return {}
+
+
+def respond_ask(reason: str, system_message: Optional[str] = None) -> None:
+    """Emit a PreToolUse response asking the user to confirm.
+
+    `reason` fills the modal body (permissionDecisionReason).
+    `system_message`, if set, surfaces a secondary banner/warning to the
+    user in a slot distinct from the modal.
+    """
+    output: dict = {
+        "hookSpecificOutput": {
+            "hookEventName": "PreToolUse",
+            "permissionDecision": "ask",
+            "permissionDecisionReason": reason,
+        }
+    }
+    if system_message:
+        output["systemMessage"] = system_message
+    print(json.dumps(output))
+
+
+def scan_attribution(text: str) -> list[str]:
+    """Return human-readable descriptions of any AI-attribution hits."""
+    if not text:
+        return []
+    hits: list[str] = []
+    for pattern, description in ATTRIBUTION_PATTERNS:
+        if re.search(pattern, text, re.IGNORECASE):
+            hits.append(description)
+    return hits
-- 
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