fix: avoid adaptive title refresh session lock deadlock

api/streaming.py

@@ -938,7 +938,12 @@ def _fallback_title_from_exchange(user_text: str, assistant_text: str) -> Option
         'need', 'needs', 'want', 'wants', 'user', 'assistant', 'could', 'would',
         'should', 'about', 'there', 'here', 'test', 'testing', 'title', 'summary',
     }
-    tokens = re.findall(r'[A-Za-z0-9][A-Za-z0-9_./+-]*', head)
+    # Unicode-aware Latin tokenization: keep the old "no leading underscore"
+    # and non-Latin placeholder behavior while allowing letters such as ä/ö/ü/ß.
+    # The previous ASCII-only pattern turned "führe" into "f" + "hre"; the short
+    # "f" was filtered and the broken "hre" became part of the title.
+    latin_word = r'A-Za-z0-9À-ÖØ-öø-ÿ'
+    tokens = re.findall(rf'[{latin_word}][{latin_word}_./+-]*', head)
     if not tokens:
         return 'Conversation topic'
 
@@ -1092,8 +1097,12 @@ def _run_background_title_refresh(session_id: str, user_text: str, assistant_tex
                     return
                 s.title = next_title
                 s.llm_title_generated = True
-                s.save(touch_updated_at=False)
                 effective_title = s.title
+            # Session.save() calls _write_session_index(), which acquires LOCK.
+            # Keep the per-session agent lock for mutation serialization, but
+            # release the global session LOCK before persisting to avoid a
+            # self-deadlock in the background title-refresh thread.
+            s.save(touch_updated_at=False)
         _put_title_status(put_event, session_id, 'refreshed', llm_status, effective_title, raw_preview)
         put_event('title', {'session_id': session_id, 'title': effective_title})
         logger.info("Adaptive title refresh: session=%s new_title=%r", session_id, effective_title)

tests/test_1058_adaptive_title_refresh.py

@@ -287,6 +287,40 @@ class TestRunBackgroundTitleRefresh:
         assert len(title_events) == 1
         assert title_events[0][1]['title'] == 'New Refreshed Title'
 
+    def test_saves_refreshed_title_outside_global_lock(self):
+        """Refreshing an existing title must not call Session.save() while holding LOCK."""
+        class TrackingLock:
+            def __init__(self):
+                self.held = False
+
+            def __enter__(self):
+                assert not self.held
+                self.held = True
+                return self
+
+            def __exit__(self, exc_type, exc, tb):
+                self.held = False
+
+        put, events = self._make_put_event()
+        lock = TrackingLock()
+        s = self._make_session_obj(title='Old Title')
+
+        def save(*args, **kwargs):
+            assert not lock.held, "Session.save() must run outside api.models.LOCK"
+
+        s.save = save
+        fake_sessions = {'sid': s}
+        with patch('api.streaming.get_session', return_value=s), \
+             patch('api.streaming._aux_title_configured', return_value=True), \
+             patch('api.streaming._generate_llm_session_title_via_aux',
+                   return_value=('New Refreshed Title', 'llm_ok', 'raw')), \
+             patch('api.streaming.SESSIONS', fake_sessions), \
+             patch('api.streaming.LOCK', lock):
+            _run_background_title_refresh('sid', 'u', 'a', 'Old Title', put)
+        title_events = [(n, d) for n, d in events if n == 'title']
+        assert len(title_events) == 1
+        assert title_events[0][1]['title'] == 'New Refreshed Title'
+
     def test_exceptions_are_silently_swallowed(self):
         """Any unexpected error inside must not propagate — it's a background daemon."""
         put, events = self._make_put_event()

tests/test_sprint41.py

@@ -327,6 +327,19 @@ class TestIssue495TitleStreaming(unittest.TestCase):
             "Substantive answer text on a tool_call row must be preserved",
         )
 
+    def test_fallback_title_preserves_unicode_letters(self):
+        """Local fallback title generation must not strip German umlauts."""
+        from api.streaming import _fallback_title_from_exchange
+
+        title = _fallback_title_from_exchange(
+            "Bitte führe ein Selbst-Audit durch. Wo ist überall noch Gemini-2.5-flash als Modell im Einsatz? Sei gründlich",
+            "Ich prüfe live statt aus Bauchgefühl.",
+        )
+
+        self.assertIsNotNone(title)
+        self.assertIn("führe", title)
+        self.assertNotIn("hre", title.split())
+
     def test_title_snippet_skips_tool_call_preamble_only_rows(self):
         """Tool-call rows whose content is empty or meta-reasoning preamble
         ('Let me check my memory first.') must still be skipped — those are