feat(assistant): implement spec 021 chat assistant flow with semantic contracts

backend/src/core/database.py

@@ -1,11 +1,12 @@
 # [DEF:backend.src.core.database:Module]
 #
+# @TIER:      STANDARD
 # @SEMANTICS: database, postgresql, sqlalchemy, session, persistence
 # @PURPOSE:   Configures database connection and session management (PostgreSQL-first).
 # @LAYER:     Core
 # @RELATION:  DEPENDS_ON -> sqlalchemy
-# @RELATION:  USES -> backend.src.models.mapping
-# @RELATION:  USES -> backend.src.core.auth.config
+# @RELATION:  DEPENDS_ON -> backend.src.models.mapping
+# @RELATION:  DEPENDS_ON -> backend.src.core.auth.config
 #
 # @INVARIANT: A single engine instance is used for the entire application.
 
@@ -18,6 +19,7 @@ from ..models import task as _task_models  # noqa: F401
 from ..models import auth as _auth_models  # noqa: F401
 from ..models import config as _config_models  # noqa: F401
 from ..models import llm as _llm_models  # noqa: F401
+from ..models import assistant as _assistant_models  # noqa: F401
 from .logger import belief_scope
 from .auth.config import auth_config
 import os
@@ -72,18 +74,21 @@ auth_engine = _build_engine(AUTH_DATABASE_URL)
 # [/DEF:auth_engine:Variable]
 
 # [DEF:SessionLocal:Class]
+# @TIER: TRIVIAL
 # @PURPOSE: A session factory for the main mappings database.
 # @PRE: engine is initialized.
 SessionLocal = sessionmaker(autocommit=False, autoflush=False, bind=engine)
 # [/DEF:SessionLocal:Class]
 
 # [DEF:TasksSessionLocal:Class]
+# @TIER: TRIVIAL
 # @PURPOSE: A session factory for the tasks execution database.
 # @PRE: tasks_engine is initialized.
 TasksSessionLocal = sessionmaker(autocommit=False, autoflush=False, bind=tasks_engine)
 # [/DEF:TasksSessionLocal:Class]
 
 # [DEF:AuthSessionLocal:Class]
+# @TIER: TRIVIAL
 # @PURPOSE: A session factory for the authentication database.
 # @PRE: auth_engine is initialized.
 AuthSessionLocal = sessionmaker(autocommit=False, autoflush=False, bind=auth_engine)