fix: strip @provider: prefix from auxiliary title_generation model id (#3430, @pamnard)

Manual title regeneration (POST /api/session/title/regenerate) and background
aux title generation failed with 422 / llm_error_aux when
auxiliary.title_generation.model in config.yaml used the WebUI-internal
@provider:model picker format (e.g. @gemini:gemini-3.1-flash-lite) — the raw
@-qualified id was forwarded to the provider API verbatim. Normalize it through
the canonical _split_webui_provider_model_value() helper before the aux call.

Co-authored-by: pamnard <pamnard@users.noreply.github.com>

api/streaming.py

@@ -1801,6 +1801,17 @@ def generate_title_raw_via_aux(
         provider = ''
     model = model or configured.get('model', '') or ''
     base_url = base_url or configured.get('base_url', '') or ''
+    try:
+        from api.profiles import _split_webui_provider_model_value
+
+        normalized_model, normalized_provider = _split_webui_provider_model_value(
+            model or None,
+            provider or None,
+        )
+        model = normalized_model or ''
+        provider = normalized_provider or ''
+    except ValueError:
+        pass
     api_key = ''
     if not caller_supplied_route:
         api_key = str(configured.get('api_key', '') or '').strip()

tests/test_title_aux_routing.py

@@ -109,6 +109,41 @@ class TestGenerateTitleRawViaAuxTimeout(unittest.TestCase):
             30.0,
         )
 
+    def test_webui_prefixed_model_id_is_stripped_before_aux_call(self):
+        """Regression: @provider:model picker ids must not reach provider APIs verbatim."""
+        from api.streaming import generate_title_raw_via_aux
+
+        mock_resp = types.SimpleNamespace(
+            choices=[
+                types.SimpleNamespace(
+                    message=types.SimpleNamespace(content='Gemini Title'),
+                    finish_reason='stop',
+                )
+            ]
+        )
+        captured = {}
+
+        def fake_call_llm(**kwargs):
+            captured.update(kwargs)
+            return mock_resp
+
+        tg_config = {
+            'provider': 'gemini',
+            'model': '@gemini:gemini-3.1-flash-lite',
+            'base_url': '',
+        }
+        with _patch_tg_config(tg_config):
+            with patch('agent.auxiliary_client.call_llm', side_effect=fake_call_llm, create=True):
+                result, status = generate_title_raw_via_aux(
+                    user_text='Как настроить title generation?',
+                    assistant_text='Нужно указать auxiliary.title_generation в config.yaml.',
+                )
+
+        self.assertEqual(result, 'Gemini Title')
+        self.assertEqual(status, 'llm_aux')
+        self.assertEqual(captured.get('provider'), 'gemini')
+        self.assertEqual(captured.get('model'), 'gemini-3.1-flash-lite')
+
     def test_configured_provider_model_and_base_url_are_passed_to_aux_client(self):
         """Regression for #2235: task config must select the first title model.