fix: harden bucket file serving

Dockerfile

@@ -1,5 +1,7 @@
 FROM python:3.12-slim
 
+ARG LEADERBOARD_BUILD_ID=20260620_leaderboard_slug
+
 WORKDIR /app
 
 COPY requirements.txt .

app.py

@@ -12,7 +12,7 @@ from pathlib import Path
 from typing import Any
 
 from fastapi import FastAPI, Header, HTTPException
-from fastapi.responses import FileResponse, HTMLResponse, JSONResponse
+from fastapi.responses import HTMLResponse, JSONResponse, Response
 
 from leaderboard_core import DEFAULT_MAX_AGE_DAYS, DEFAULT_MIN_DOWNLOADS, DEFAULT_TOP_N, refresh
 
@@ -65,7 +65,18 @@ def latest_json() -> Path:
 def read_json(path: Path) -> dict[str, Any]:
     if not path.exists():
         return {}
-    return json.loads(path.read_text(encoding="utf-8"))
+    try:
+        return json.loads(path.read_text(encoding="utf-8"))
+    except Exception as err:  # noqa: BLE001
+        print(f"failed to read json {path}: {err}", flush=True)
+        return {}
+
+
+def file_size(path: Path) -> int | None:
+    try:
+        return path.stat().st_size
+    except OSError:
+        return None
 
 
 def run_refresh() -> dict[str, Any]:
@@ -144,7 +155,7 @@ def loading_page() -> str:
 def index():
     path = latest_html()
     if path.exists():
-        return FileResponse(path, media_type="text/html")
+        return HTMLResponse(path.read_text(encoding="utf-8"))
     return HTMLResponse(loading_page(), status_code=202)
 
 
@@ -155,23 +166,26 @@ def healthz() -> dict[str, Any]:
         "data_dir": str(data_dir()),
         "has_html": latest_html().exists(),
         "has_json": latest_json().exists(),
+        "html_size": file_size(latest_html()),
+        "json_size": file_size(latest_json()),
+        "summary_size": file_size(latest_dir() / "summary.json"),
     }
 
 
 @app.get("/api/summary", response_model=None)
 def api_summary():
-    payload = read_json(latest_dir() / "summary.json")
-    if not payload:
+    path = latest_dir() / "summary.json"
+    if not path.exists():
         return JSONResponse({"status": "initializing"}, status_code=202)
-    return JSONResponse(payload)
+    return Response(path.read_bytes(), media_type="application/json")
 
 
 @app.get("/api/leaderboard", response_model=None)
 def api_leaderboard():
-    payload = read_json(latest_json())
-    if not payload:
+    path = latest_json()
+    if not path.exists():
         return JSONResponse({"status": "initializing"}, status_code=202)
-    return JSONResponse(payload)
+    return Response(path.read_bytes(), media_type="application/json")
 
 
 @app.get("/latest/{filename}", response_model=None)
@@ -185,7 +199,7 @@ def latest_file(filename: str):
     media_type = "application/json" if filename.endswith(".json") else "text/plain"
     if filename.endswith(".csv"):
         media_type = "text/csv"
-    return FileResponse(path, media_type=media_type)
+    return Response(path.read_bytes(), media_type=media_type)
 
 
 @app.post("/api/refresh", response_model=None)