fix(matrix): strip only explicit @mentions in _strip_mention

tests/gateway/test_matrix_mention.py

@@ -159,7 +159,7 @@ class TestStripMention:
         assert result == "help me"
 
     def test_localpart_preserved(self):
-        """Localpart-only text is no longer stripped — avoids false positives in paths."""
+        """Bare localpart (no @) is preserved — avoids false positives in paths."""
         result = self.adapter._strip_mention("hermes help me")
         assert result == "hermes help me"
 
@@ -168,6 +168,15 @@ class TestStripMention:
         result = self.adapter._strip_mention("read /home/hermes/config.yaml")
         assert result == "read /home/hermes/config.yaml"
 
+    def test_strip_localpart_when_explicit_at_mention(self):
+        result = self.adapter._strip_mention("@hermes help me")
+        assert result == "help me"
+
+    def test_does_not_strip_bare_localpart_word(self):
+        # Regression: plain words like "Hermes Agent" should not be mutated.
+        result = self.adapter._strip_mention("Hermes Agent")
+        assert result == "Hermes Agent"
+
     def test_strip_returns_empty_for_mention_only(self):
         result = self.adapter._strip_mention("@hermes:example.org")
         assert result == ""