db: prefer bucket-mounted /data/lineage.db with baked-in fallback

app.py

@@ -18,7 +18,13 @@ from fastapi import FastAPI, Query, Request
 from fastapi.middleware.gzip import GZipMiddleware
 from fastapi.responses import HTMLResponse, JSONResponse
 
-DB = Path(__file__).parent / "lineage.db"
+# Prefer the bucket-mounted DB (/data/lineage.db, persistent + can grow);
+# fall back to the baked-in copy if the mount isn't present (cold-mount fail,
+# local dev, etc.) so the Space stays up either way.
+BUCKET_DB = Path("/data/lineage.db")
+LOCAL_DB = Path(__file__).parent / "lineage.db"
+DB = BUCKET_DB if BUCKET_DB.exists() else LOCAL_DB
+print(f"using DB: {DB} (bucket-mount={BUCKET_DB.exists()})", flush=True)
 # High safety ceiling only — stops a depth-2 hub exploding to tens of thousands
 # of nodes. Normal hubs (incl. FLAN's ~1.4k children) render fully.
 MAX_NODES = 2500