feat(backends,storage,core,markdown,infra): claude agent sdk backend, session store, transcript seeding, runner isolation

src/beaver_gateway/storage/db.py

@@ -22,7 +22,7 @@ from sqlalchemy.ext.asyncio import create_async_engine
 from sqlmodel import SQLModel, select
 from sqlmodel.ext.asyncio.session import AsyncSession
 
-from beaver_gateway.storage.models import AuditLog, Token
+from beaver_gateway.storage.models import AuditLog, Token, Usage
 
 if TYPE_CHECKING:
     from collections.abc import Sequence
@@ -183,9 +183,18 @@ async def list_audit_records(
     return result.all()
 
 
+# ---- Usage --------------------------------------------------------------
+
+
+async def append_usage(session: AsyncSession, row: Usage) -> None:
+    session.add(row)
+    await session.commit()
+
+
 __all__ = [
     "Database",
     "append_audit",
+    "append_usage",
     "create_token",
     "list_active_tokens",
     "list_audit_records",