Improve L1 fetch error handling with better diagnostics

- Handle 404 explicitly with clear "not found" message
- Log actual response body when JSON parsing fails
- Include status code and body preview in error messages

This helps diagnose issues like empty responses or HTML error pages from L1.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

server.py

@@ -1787,20 +1787,33 @@ async def record_run(req: RecordRunRequest, user: User = Depends(get_required_us
 
     # Helper to fetch from L1 without blocking event loop
     def fetch_l1_run():
-        logger.info(f"record_run: Fetching run from L1: {l1_url}/runs/{req.run_id}")
-        resp = requests.get(f"{l1_url}/runs/{req.run_id}", timeout=30)
+        url = f"{l1_url}/runs/{req.run_id}"
+        logger.info(f"record_run: Fetching run from L1: {url}")
+        resp = requests.get(url, timeout=30)
+        if resp.status_code == 404:
+            raise ValueError(f"Run not found on L1: {req.run_id}")
         resp.raise_for_status()
-        return resp.json()
+        try:
+            return resp.json()
+        except Exception:
+            body_preview = resp.text[:200] if resp.text else "(empty)"
+            logger.error(f"L1 returned non-JSON for {url}: status={resp.status_code}, body={body_preview}")
+            raise ValueError(f"L1 returned invalid response: {body_preview[:100]}")
 
     def fetch_l1_cache(content_hash):
         logger.debug(f"record_run: Fetching cache {content_hash[:16]}... from L1")
-        resp = requests.get(
-            f"{l1_url}/cache/{content_hash}",
-            headers={"Accept": "application/json"},
-            timeout=10
-        )
+        url = f"{l1_url}/cache/{content_hash}"
+        resp = requests.get(url, headers={"Accept": "application/json"}, timeout=10)
+        if resp.status_code == 404:
+            raise ValueError(f"Cache item not found on L1: {content_hash[:16]}...")
         resp.raise_for_status()
-        return resp.json()
+        try:
+            return resp.json()
+        except Exception as e:
+            # Log what we actually got back
+            body_preview = resp.text[:200] if resp.text else "(empty)"
+            logger.error(f"L1 returned non-JSON for {url}: status={resp.status_code}, body={body_preview}")
+            raise ValueError(f"L1 returned invalid response (status={resp.status_code}): {body_preview[:100]}")
 
     # Fetch run from L1
     try: