diff --git a/scripts/check-attribution-trailers.sh b/scripts/check-attribution-trailers.sh
index 1eb96dbc..300e7e88 100755
--- a/scripts/check-attribution-trailers.sh
+++ b/scripts/check-attribution-trailers.sh
@@ -2,14 +2,51 @@
 # Flags Co-Authored-By trailers with Claude/Anthropic attribution in PR commits.
 # The hive convention in /knowledge/hive-rules.md forbids these trailers.
 #
-# Pattern is loose (case-insensitive, matches `claude`, `anthropic`, or
-# `noreply@anthropic.com` anywhere after `co-authored-by`) to cover variants
-# like `Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>`.
+# Pattern is anchored to an actual git trailer line — `^[[:space:]]*co-authored-by:`
+# — not any mention of the phrase, then requires the value name `claude`,
+# `anthropic`, or `noreply@anthropic.com`. Matching is case-insensitive and
+# per-line (git trailers are one `Key: value` per line) to cover variants like
+# `Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>` while letting a
+# commit subject/body that merely *discusses* the trailer (e.g. this script's
+# own "add CI lint for Co-Authored-By/Claude/Anthropic trailers") pass.
 #
 # Scope is the PR's commits (BASE..HEAD), not entire history — old commits
 # must not fail the build.
+#
+# Run with --self-test to check the pattern against fixtures instead of
+# scanning git history.
 set -eu
 
+trailer_re='^[[:space:]]*co-authored-by:.*(claude|anthropic|noreply@anthropic\.com)'
+
+if [ "${1:-}" = "--self-test" ]; then
+  fail=0
+
+  assert_match() {
+    if ! printf '%s\n' "$2" | grep -qiE "$trailer_re"; then
+      echo "self-test FAILED (expected match): $1" >&2
+      fail=1
+    fi
+  }
+  assert_no_match() {
+    if printf '%s\n' "$2" | grep -qiE "$trailer_re"; then
+      echo "self-test FAILED (expected no match): $1" >&2
+      fail=1
+    fi
+  }
+
+  assert_match "bare trailer" 'Co-Authored-By: Claude'
+  assert_match "full trailer with email" 'Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>'
+  assert_match "lowercase trailer" 'co-authored-by: claude'
+  assert_no_match "ordinary message" 'fix: correct off-by-one in parser'
+  assert_no_match "prose mention of the trailer" 'ops: add CI lint for Co-Authored-By/Claude/Anthropic trailers'
+
+  if [ "$fail" -eq 0 ]; then
+    echo "self-test OK"
+  fi
+  exit "$fail"
+fi
+
 if [ -n "${GITHUB_BASE_REF:-}" ]; then
   base="origin/${GITHUB_BASE_REF}"
 else
@@ -35,7 +72,7 @@ fi
 hits=""
 for sha in $commits; do
   msg="$(git log -1 --format='%B' "$sha")"
-  if printf '%s\n' "$msg" | grep -qiE 'co-authored-by.*claude|co-authored-by.*anthropic|co-authored-by.*noreply@anthropic\.com'; then
+  if printf '%s\n' "$msg" | grep -qiE "$trailer_re"; then
     subject="$(git log -1 --format='%s' "$sha")"
     hits="${hits}${sha}|${subject}
 "