Harden multi-user activity fetching

tests/test_main.py

@@ -1,9 +1,13 @@
+import tempfile
 from datetime import date
+from pathlib import Path
 
 import pytest
 
-from app.main import QueryOptions, collect_merged_activity
+from app.main import QueryOptions, collect_merged_activity, _fetch_source_usernames
+from app.cache import FileCache
 from app.settings import Settings
+from app.sources import github as github_source
 
 
 @pytest.mark.asyncio
@@ -38,3 +42,65 @@ async def test_collect_merged_activity_combines_multiple_usernames(monkeypatch)
     assert sorted(github_calls) == ["hubot", "octocat"]
     assert sorted(gitea_calls) == ["alice", "bob"]
     assert result.merged["2026-01-01"] == {"github": 3, "gitea": 7, "total": 10}
+
+
+@pytest.mark.asyncio
+async def test_fetch_source_usernames_skips_failed_accounts() -> None:
+    async def ok_fetch():
+        return {"2026-01-01": 2}
+
+    async def bad_fetch():
+        raise github_source.GitHubSourceError("boom")
+
+    result, stale = await _fetch_source_usernames(
+        None,
+        "github",
+        ["octocat", "hubot"],
+        date(2026, 1, 1),
+        date(2026, 1, 1),
+        lambda username: ok_fetch if username == "octocat" else bad_fetch,
+    )
+
+    assert result == {"2026-01-01": 2}
+    assert stale is False
+
+
+@pytest.mark.asyncio
+async def test_fetch_source_usernames_keeps_cache_after_username_list_changes() -> None:
+    with tempfile.TemporaryDirectory(dir=Path.cwd()) as temp_dir:
+        cache = FileCache(cache_dir=temp_dir, default_ttl_seconds=0)
+
+        def prime_fetcher(username):
+            async def fetch():
+                return {"2026-01-01": 1}
+
+            return fetch
+
+        await _fetch_source_usernames(
+            cache,
+            "github",
+            ["octocat"],
+            date(2026, 1, 1),
+            date(2026, 1, 1),
+            prime_fetcher,
+        )
+
+        def fetch_after_change(username):
+            async def fetch():
+                if username == "octocat":
+                    raise github_source.GitHubSourceError("down")
+                return {"2026-01-01": 2}
+
+            return fetch
+
+        result, stale = await _fetch_source_usernames(
+            cache,
+            "github",
+            ["octocat", "hubot"],
+            date(2026, 1, 1),
+            date(2026, 1, 1),
+            fetch_after_change,
+        )
+
+        assert result == {"2026-01-01": 3}
+        assert stale is True