M16: isolate acceptance and harden readiness

backend/app/main.py

@@ -4,6 +4,7 @@ from contextlib import asynccontextmanager
 from fastapi import FastAPI, HTTPException, Request
 from fastapi.middleware.cors import CORSMiddleware
 from fastapi.responses import JSONResponse
+from sqlalchemy import text
 
 from app.api.routers import (
     audit,
@@ -77,6 +78,28 @@ def health() -> dict[str, str]:
     return {"status": "ok", "service": "mobilityops-api"}
 
 
+@app.get("/health/live")
+def liveness() -> dict[str, str]:
+    """Process liveness only; external dependencies deliberately do not affect it."""
+    return {"status": "ok", "service": "mobilityops-api"}
+
+
+@app.get("/health/ready")
+def readiness() -> JSONResponse:
+    """Traffic readiness: the API is useful only while its canonical database responds."""
+    try:
+        with SessionLocal() as db:
+            db.execute(text("SELECT 1"))
+    except Exception:  # noqa: BLE001 -- readiness must convert infrastructure errors to 503
+        return JSONResponse(
+            status_code=503,
+            content={"status": "not_ready", "service": "mobilityops-api", "database": "down"},
+        )
+    return JSONResponse(
+        content={"status": "ready", "service": "mobilityops-api", "database": "up"}
+    )
+
+
 @app.get("/api/v1/system/status")
 def system_status() -> dict[str, object]:
     return {