diff --git a/tools/ci/src/commit-attribution.ts b/tools/ci/src/commit-attribution.ts
index c137847bd..340553fa6 100644
--- a/tools/ci/src/commit-attribution.ts
+++ b/tools/ci/src/commit-attribution.ts
@@ -22,8 +22,10 @@ export function hasAICoauthor(message: string): boolean {
     encoding: 'utf8'
   })
   return trailers.split('\n').some((line) => {
-    const email = /^co-authored-by:\s*.*<([^<>]+)>\s*$/i.exec(line)?.[1]?.trim().toLowerCase()
-    return email !== undefined && (AI_COAUTHOR_EMAILS.has(email) || AI_GITHUB_EMAIL.test(email))
+    const value = /^co-authored-by:\s*(.*)$/i.exec(line)?.[1]?.trim()
+    if (!value) return false
+    const email = (/<([^<>]+)>$/.exec(value)?.[1] ?? value).trim().toLowerCase()
+    return AI_COAUTHOR_EMAILS.has(email) || AI_GITHUB_EMAIL.test(email)
   })
 }
 
diff --git a/tools/ci/tests/commit-messages.test.ts b/tools/ci/tests/commit-messages.test.ts
index b33df173c..75f910c21 100644
--- a/tools/ci/tests/commit-messages.test.ts
+++ b/tools/ci/tests/commit-messages.test.ts
@@ -39,6 +39,7 @@ test.each([
 test.each([
   'fix: document Claude Code and OpenAI integration',
   'fix: preserve credits\n\nCo-authored-by: Claude Martin <claude@example.org>',
+  'fix: preserve credits\n\nCo-authored-by: person@example.org',
   'fix: preserve credits\n\nCo-authored-by: Claude <123+claude@users.noreply.github.com>',
   'fix: preserve credits\n\nCo-authored-by: Codex <456+codex@users.noreply.github.com>',
   'fix: preserve credits\n\nCo-authored-by: Human Contributor <person@anthropic.com>',
@@ -49,6 +50,8 @@ test.each([
 
 test.each([
   'Claude Sonnet 5 <noreply@anthropic.com>',
+  'noreply@anthropic.com',
+  'NOREPLY@OPENAI.COM',
   'Codex <codex@openai.com>',
   'Cursor <noreply@cursor.com>',
   'Gemini CLI <gemini-cli@google.com>',
@@ -84,6 +87,15 @@ test.each([
   expect(result.output).toContain('Preserve human co-author credits')
 })
 
+test.each(['fix: update', 'Release v0.14.0'])(
+  'rejects bare assistant email trailers: %s',
+  async (subject) => {
+    const result = await lint(`${subject}\n\nCo-authored-by: noreply@anthropic.com`)
+    expect(result.code).not.toBe(0)
+    expect(result.output).toContain('no-ai-coauthors')
+  }
+)
+
 test.each([
   ['Fixed stuff', 'type-empty'],
   ['feature: add tools', 'type-enum'],