feat(07-03): classifier wired to load_provider_config + ai_config stub removed — D-04/D-06

- Remove _ProviderConfigStub from services/ai_config.py (replaced by real ProviderConfig)
- Add module-level import: from ai.provider_config import ProviderConfig, PROVIDER_DEFAULTS
- load_provider_config() now returns ProviderConfig (no lazy import inside function body)
- classifier.py: replace inline _settings dict with load_provider_config(session) call (D-06)
- Per-user override path builds ProviderConfig from PROVIDER_DEFAULTS (no api_key — T-07-06)
- Fallback to app_settings defaults when load_provider_config returns None (D-15)
- Truncation delegated to provider._truncate() — no more text slices in classifier (D-12/D-13)
- Promote test_api_key_encrypt_decrypt to passing (round-trip + domain salt isolation)
- Update test_classifier.py: test_per_user_provider + test_default_provider_fallback use ProviderConfig assertions

backend/tests/test_classifier.py

@@ -119,13 +119,17 @@ async def test_classifier_with_mock_provider(isolated_data_dir):
 @pytest.mark.asyncio
 async def test_per_user_provider(db_session):
     """When ai_provider='openai' and ai_model='gpt-4o' are passed to the classifier,
-    it resolves _settings['active_provider'] == 'openai'.
+    it builds a ProviderConfig with provider_id='openai' and model='gpt-4o'.
 
     DOC-03: AI provider/model comes from the user's DB record (passed through from
     _run) not from global config or the retired load_settings() flat file (D-14).
+
+    Plan 07-03: get_provider now receives a ProviderConfig object (D-06), not a
+    raw dict. Assertions updated accordingly.
     """
     from unittest.mock import AsyncMock, patch, MagicMock
     from ai.base import ClassificationResult
+    from ai.provider_config import ProviderConfig
     from services.classifier import classify_document
     import uuid
 
@@ -136,10 +140,10 @@ async def test_per_user_provider(db_session):
     mock_doc = MagicMock()
     mock_doc.user_id = user_id
 
-    captured_settings = {}
+    captured_configs = []
 
-    def capture_get_provider(settings):
-        captured_settings.update(settings)
+    def capture_get_provider(config):
+        captured_configs.append(config)
         mock_provider = MagicMock()
         mock_provider.classify = AsyncMock(return_value=ClassificationResult(
             topics=[], suggested_new_topics=[], reasoning=""
@@ -156,9 +160,11 @@ async def test_per_user_provider(db_session):
          patch("services.classifier.get_provider", side_effect=capture_get_provider):
         await classify_document(mock_session, doc_id, ai_provider="openai", ai_model="gpt-4o")
 
-    assert captured_settings.get("active_provider") == "openai"
-    assert "openai" in captured_settings.get("providers", {})
-    assert captured_settings["providers"]["openai"]["model"] == "gpt-4o"
+    assert len(captured_configs) == 1
+    config = captured_configs[0]
+    assert isinstance(config, ProviderConfig), "get_provider must receive a ProviderConfig (D-06)"
+    assert config.provider_id == "openai"
+    assert config.model == "gpt-4o"
 
 
 @pytest.mark.asyncio
@@ -224,13 +230,18 @@ async def test_celery_task_uses_user_provider(db_session):
 
 @pytest.mark.asyncio
 async def test_default_provider_fallback(db_session):
-    """When user.ai_provider is None, the classifier receives config.settings.default_ai_provider.
+    """When user.ai_provider is None, the classifier uses the system_settings DB row or env fallback.
 
-    D-15: fallback chain is user.ai_provider → DEFAULT_AI_PROVIDER env var →
+    D-15: fallback chain is user.ai_provider → system_settings DB → DEFAULT_AI_PROVIDER env var →
     code default 'ollama' (CONTEXT.md D-15).
+
+    Plan 07-03: get_provider now receives a ProviderConfig (D-06). When ai_provider=None
+    and load_provider_config returns None, the classifier falls back to
+    app_settings.default_ai_provider. Assertions updated from dict to ProviderConfig.
     """
     from unittest.mock import AsyncMock, patch, MagicMock
     from ai.base import ClassificationResult
+    from ai.provider_config import ProviderConfig
     from services.classifier import classify_document
     import uuid
 
@@ -241,10 +252,10 @@ async def test_default_provider_fallback(db_session):
     mock_doc = MagicMock()
     mock_doc.user_id = user_id
 
-    captured_settings = {}
+    captured_configs = []
 
-    def capture_get_provider(settings):
-        captured_settings.update(settings)
+    def capture_get_provider(config):
+        captured_configs.append(config)
         mock_provider = MagicMock()
         mock_provider.classify = AsyncMock(return_value=ClassificationResult(
             topics=[], suggested_new_topics=[], reasoning=""
@@ -255,6 +266,7 @@ async def test_default_provider_fallback(db_session):
          patch("services.classifier.storage.load_topics_for_user", AsyncMock(return_value=[])), \
          patch("services.classifier.storage.load_topics", AsyncMock(return_value=[])), \
          patch("services.classifier.storage.update_document_topics", AsyncMock(return_value=None)), \
+         patch("services.classifier.load_provider_config", AsyncMock(return_value=None)), \
          patch("services.classifier.get_provider", side_effect=capture_get_provider):
 
         mock_session = AsyncMock()
@@ -262,5 +274,8 @@ async def test_default_provider_fallback(db_session):
         # Pass ai_provider=None to trigger the default fallback (D-15)
         await classify_document(mock_session, doc_id, ai_provider=None, ai_model=None)
 
+    assert len(captured_configs) == 1
+    config = captured_configs[0]
+    assert isinstance(config, ProviderConfig), "get_provider must receive a ProviderConfig (D-06)"
     # Should fall back to app_settings.default_ai_provider = "ollama"
-    assert captured_settings.get("active_provider") == "ollama"
+    assert config.provider_id == "ollama"