Harden multi-user activity fetching

app/main.py

@@ -125,22 +125,47 @@ async def _fetch_source_usernames(
     if not usernames:
         return {}, False
 
-    cache_usernames = hashlib.sha1(",".join(sorted(usernames)).encode("utf-8")).hexdigest()[:12]
-    fetch_tasks: list[asyncio.Task[tuple[dict[str, int], bool]]] = []
+    fetch_tasks: list[asyncio.Task[tuple[str, tuple[dict[str, int], bool] | Exception]]] = []
     for username in usernames:
-        key = f"{source_prefix}_{cache_usernames}_{username}_{from_date}_{to_date}"
-        fetch_tasks.append(asyncio.create_task(_fetch_with_cache(cache, key, fetcher_factory(username))))
+        key = f"{source_prefix}_{username}_{from_date}_{to_date}"
+        fetch_tasks.append(
+            asyncio.create_task(
+                _fetch_source_username(cache, key, username, fetcher_factory(username))
+            )
+        )
 
     combined: dict[str, int] = {}
     stale = False
-    for data, entry_stale in await asyncio.gather(*fetch_tasks):
+    failures: list[Exception] = []
+    for username, result in await asyncio.gather(*fetch_tasks):
+        if isinstance(result, Exception):
+            logger.warning("source fetch failed for %s/%s, skipping user: %s", source_prefix, username, result)
+            failures.append(result)
+            continue
+
+        data, entry_stale = result
         stale = stale or entry_stale
         for day, count in data.items():
             combined[day] = combined.get(day, 0) + int(count)
 
+    if not combined and failures:
+        raise failures[0]
+
     return combined, stale
 
 
+async def _fetch_source_username(
+    cache: FileCache | None,
+    key: str,
+    username: str,
+    fetcher,
+) -> tuple[str, tuple[dict[str, int], bool] | Exception]:
+    try:
+        return username, await _fetch_with_cache(cache, key, fetcher)
+    except Exception as exc:
+        return username, exc
+
+
 async def collect_merged_activity(
     settings: Settings,
     cache: FileCache | None,