fix(agents): normalize possessive federated handles

tools/skills/validate-agent-guidance.mjs

@@ -228,7 +228,7 @@ export async function validateAgentGuidance({ rootDir }) {
                 if (isPackageMention(token)) continue;
                 if (
                     /^[\w.-]+@(?:[a-z\d](?:[a-z\d-]*[a-z\d])?\.)+[a-z]{2,}$/iu.test(
-                        token.replace(/\p{P}+$/gu, '')
+                        token.replace(/\p{P}+$/gu, '').replace(/['’]s$/iu, '')
                     )
                 )
                     continue;

tools/skills/validate-agent-guidance.test.mjs

@@ -1778,3 +1778,15 @@ for (const suffix of ['…', '。', '！', '—']) {
         );
     });
 }
+
+for (const suffix of ["'s", '’s']) {
+    test(`federated handle may be possessive: ${suffix}`, async (t) => {
+        assert.deepEqual(
+            await diagnostics(t, {
+                'AGENTS.md':
+                    'Contact @alice@example.social' + suffix + ' administrator',
+            }),
+            []
+        );
+    });
+}