fix(health): use injected session instead of global engine pool

The /state/health probe now depends on get_session so pytest's
dependency override routes through the test engine. Using engine.connect()
directly caused asyncpg pool teardown failures (Event loop is closed) late
in the full suite.

api/routers/state.py

@@ -7,7 +7,7 @@ from sqlalchemy import func, select, text
 from sqlalchemy.ext.asyncio import AsyncSession
 from sqlalchemy.orm import noload, selectinload
 
-from api.database import get_session, engine
+from api.database import get_session
 from api.flow_defs import assertion_result_to_dict, load_flow
 from api.models.capability_request import CapabilityRequest
 from api.models.contribution import Contribution, ContributionStatus, ContributionType
@@ -1024,10 +1024,9 @@ async def get_next_steps(session: AsyncSession = Depends(get_session)) -> list[N
 
 
 @router.get("/health")
-async def health_check() -> dict:
+async def health_check(session: AsyncSession = Depends(get_session)) -> dict:
     try:
-        async with engine.connect() as conn:
-            await conn.execute(text("SELECT 1"))
+        await session.execute(text("SELECT 1"))
         return {"status": "ok", "db": "connected"}
     except Exception as exc:
         return JSONResponse(