ELO scraper: discover the embed link and retry transient failures

Read the current OneDrive link from the stat-check.com/elo iframe on
each run, falling back to EMBED_URL if the page can't be read or its
link 404s. Retry 429/5xx and network errors up to three times with
backoff, after a one-off 503 from the Badger token endpoint failed a run.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

sites/40k-rankings/statcheck-elo-scraper/download_and_parse.py

@@ -4,8 +4,10 @@ import html
 import json
 import re
 import sys
+import time
 import zipfile
 from pathlib import Path
+from urllib.error import HTTPError, URLError
 from urllib.request import Request, urlopen
 from xml.etree.ElementTree import iterparse
 
@@ -16,6 +18,27 @@ NS = {
     "pkgrel": "http://schemas.openxmlformats.org/package/2006/relationships",
 }
 
+# Seconds to wait before each retry of a transient failure.
+RETRY_DELAYS = (5, 15, 45)
+
+
+def fetch(req: Request) -> bytes:
+    """Read a URL, retrying 429/5xx responses and network errors."""
+    for attempt, delay in enumerate((*RETRY_DELAYS, None), start=1):
+        try:
+            with urlopen(req, timeout=60) as resp:
+                return resp.read()
+        except HTTPError as e:
+            if delay is None or not (e.code == 429 or e.code >= 500):
+                raise
+            reason = f"HTTP {e.code}"
+        except (URLError, TimeoutError, ConnectionError) as e:
+            if delay is None:
+                raise
+            reason = str(e)
+        print(f"  {req.full_url.split('?')[0]}: {reason}; retry {attempt} in {delay}s", file=sys.stderr)
+        time.sleep(delay)
+
 
 def metadata_download_url(capture_path: Path) -> str:
     capture = json.loads(capture_path.read_text())
@@ -29,8 +52,7 @@ def metadata_download_url(capture_path: Path) -> str:
 
 def download(url: str, output: Path) -> None:
     req = Request(url, headers={"User-Agent": "Mozilla/5.0"})
-    with urlopen(req, timeout=60) as resp:
-        output.write_bytes(resp.read())
+    output.write_bytes(fetch(req))
 
 
 def shared_strings(zf: zipfile.ZipFile) -> list[str]: