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/services/ai_config.py

@@ -22,38 +22,21 @@ from __future__ import annotations
 
 import base64
 import logging
-from typing import Optional, TYPE_CHECKING
+from typing import Optional
 
 import structlog
 from cryptography.fernet import Fernet
 from cryptography.hazmat.primitives import hashes
 from cryptography.hazmat.primitives.kdf.hkdf import HKDF
-from pydantic import BaseModel
 from sqlalchemy import select
 from sqlalchemy.ext.asyncio import AsyncSession
 
+from ai.provider_config import ProviderConfig, PROVIDER_DEFAULTS
 from config import settings
 
-# ProviderConfig redefined in ai/provider_config.py during Plan 02 —
-# load_provider_config will re-import and return that class once Plan 02 lands.
-# The stub below is removed in Plan 03 once the classifier consumes the real class.
-
-
 logger = structlog.get_logger(__name__)
 
 
-# ── Stub ProviderConfig for Plan 01 (replaced by ai/provider_config.py in Plan 02) ──
-
-class _ProviderConfigStub(BaseModel):
-    """Minimal provider config placeholder until Plan 02 creates ai/provider_config.py."""
-
-    provider_id: str
-    api_key: str = ""
-    base_url: Optional[str] = None
-    model: str = ""
-    context_chars: int = 8000
-
-
 # ── HKDF key derivation ───────────────────────────────────────────────────────
 
 def _derive_ai_settings_key(master_key: bytes, provider_id: str) -> Fernet:
@@ -125,31 +108,19 @@ def decrypt_api_key(master_key: bytes, provider_id: str, api_key_enc: str) -> st
 
 # ── Provider config loader ────────────────────────────────────────────────────
 
-async def load_provider_config(session: AsyncSession) -> Optional[_ProviderConfigStub]:
+async def load_provider_config(session: AsyncSession) -> Optional[ProviderConfig]:
     """Load the active AI provider config from the system_settings table.
 
-    Returns a _ProviderConfigStub built from the row where is_active=True,
+    Returns a ProviderConfig built from the row where is_active=True,
     decrypting api_key_enc when present.  Returns None when no active row exists.
 
-    Note: In Plan 02, this function will try to import and return ProviderConfig
-    from ai/provider_config.py instead of the stub. The import is done lazily
-    inside the function body so that Plan 01 does not depend on files that don't
-    exist yet.
-
     Args:
         session: An open AsyncSession.
 
     Returns:
-        A _ProviderConfigStub (or the real ProviderConfig from Plan 02+) if an
-        active row exists; None if the table is empty or no row is marked active.
+        A ProviderConfig if an active row exists; None if the table is empty or
+        no row is marked active.
     """
-    # Lazy import: try to use the real ProviderConfig once Plan 02 lands
-    try:
-        from ai.provider_config import ProviderConfig as _RealProviderConfig  # type: ignore[import]
-        config_cls = _RealProviderConfig
-    except ImportError:
-        config_cls = _ProviderConfigStub  # type: ignore[assignment]
-
     from db.models import SystemSettings  # local import to avoid circular deps
 
     stmt = select(SystemSettings).where(SystemSettings.is_active.is_(True))
@@ -171,7 +142,7 @@ async def load_provider_config(session: AsyncSession) -> Optional[_ProviderConfi
                 provider_id=row.provider_id,
             )
 
-    return config_cls(
+    return ProviderConfig(
         provider_id=row.provider_id,
         api_key=api_key,
         base_url=row.base_url,
@@ -208,11 +179,14 @@ async def seed_system_settings_from_env(session: AsyncSession) -> None:
         # Row already exists — never overwrite (idempotent)
         return
 
+    # Use PROVIDER_DEFAULTS context_chars for the provider, fallback to 8000
+    context_chars = PROVIDER_DEFAULTS.get(provider_id, {}).get("context_chars", 8000)
+
     # Insert default row with no API key (local providers like Ollama don't need one)
     row = SystemSettings(
         provider_id=provider_id,
         model_name=model_name,
-        context_chars=8000,
+        context_chars=context_chars,
         is_active=True,
         api_key_enc=None,
         base_url=None,