feat(git): pre-push checks Co-authored-by trailers for agents

Same substring blacklist (copilot, claude, codex, ...) is now also
applied to every Co-authored-by trailer in the commit message, not
just the author header. Agents commonly slip in via that route.

Trailers extracted with %(trailers:key=Co-authored-by,valueonly,
unfold,separator=%x1f) and split in awk on \037, which can't appear
in identity strings, so the tab-delimited record format stays
unambiguous.

To fix a flagged trailer use git commit --amend / interactive rebase
to drop the Co-authored-by line; --reset-author won't help here.

1 files changed, 14 insertions, 5 deletions

diff --git a/dot_config/git/hooks/executable_pre-push b/dot_config/git/hooks/executable_pre-push
index a57e2d5..ba7dc60 100755
--- a/dot_config/git/hooks/executable_pre-push
+++ b/dot_config/git/hooks/executable_pre-push
@@ -58,11 +58,12 @@ while read -r _local_ref local_sha remote_ref remote_sha; do
   fi
 
   # One pass: per-commit emit
-  #   SHA \t %G? \t cn \t ce \t an \t ae \t subject
-  # Tabs aren't valid in identity fields, so awk -F'\t' parses
-  # unambiguously.
+  #   SHA \t %G? \t cn \t ce \t an \t ae \t co-authored-by-list \t subject
+  # Co-authored-by trailers are joined with 0x1f (unit separator) which
+  # cannot appear in identity strings. Tabs aren't valid in identity
+  # fields either, so awk -F'\t' parses unambiguously.
   bad=$(git rev-list \
-    --format='%H%x09%G?%x09%cn%x09%ce%x09%an%x09%ae%x09%s' \
+    --format='%H%x09%G?%x09%cn%x09%ce%x09%an%x09%ae%x09%(trailers:key=Co-authored-by,valueonly,unfold,separator=%x1f)%x09%s' \
     --no-commit-header "$@" |
     awk -F'\t' \
       -v ok="$ok" \
@@ -86,7 +87,15 @@ while read -r _local_ref local_sha remote_ref remote_sha; do
         if (is_agent(tolower($5 " " $6))) {
           reasons = reasons " [agent-author=" $5 " <" $6 ">]"
         }
-        if (reasons != "") print $1 reasons "  " $7
+        if ($7 != "") {
+          n_co = split($7, coauthors, "\037")
+          for (i = 1; i <= n_co; i++) {
+            if (coauthors[i] != "" && is_agent(tolower(coauthors[i]))) {
+              reasons = reasons " [agent-coauthor=" coauthors[i] "]"
+            }
+          }
+        }
+        if (reasons != "") print $1 reasons "  " $8
       }
     ')