diff --git a/lefthook.yml b/lefthook.yml
index 77a797709..119054b6e 100644
--- a/lefthook.yml
+++ b/lefthook.yml
@@ -16,14 +16,22 @@
 # Per project policy (`--no-verify` is banned), prefer fixing the
 # finding over bypassing the hook.
 
-# Reject tool attribution trailers.
+# Commit messages. Commits are authored by the maintainer's git identity;
+# a co-author trailer is only for a contributor whose work is in the
+# commit, under their GitHub noreply address. A message is refused when it
+# carries a "Generated with" / "Generated by" line, a "<Word>-Session:"
+# trailer, or a co-author trailer with any other address.
 commit-msg:
   commands:
-    no-tooling-trailer:
+    message-trailers:
       run: |
-        if grep -qiE '^(Co-Authored-By:.*(claude|anthropic|copilot|gpt|gemini)|Claude-Session:|Generated with)' "{1}"; then
-          echo "ERROR: the commit message carries a tooling co-author trailer or session link." >&2
-          echo "Project policy: commits are authored by the maintainer's git identity alone." >&2
+        msg="{1}"
+        if grep -qiE '^[^[:alnum:]]*Generated (with|by)[[:space:]]' "$msg" ||
+          grep -qiE '^[[:alpha:]]+-Session:' "$msg" ||
+          grep -iE '^Co-authored-by:' "$msg" |
+            grep -qviE '<[^<>[:space:]]+@users\.noreply\.github\.com>[[:space:]]*$'; then
+          echo "ERROR: the commit message carries a generator line, a session trailer," >&2
+          echo "or a co-author trailer without a GitHub noreply address." >&2
           echo "Remove the offending line(s) from the message and commit again." >&2
           exit 1
         fi