Auto-download new podcast episodes from an RSS feed

A show folder under Kinderpodcasts/ opts in by containing a feed.txt marker
naming its RSS feed. A new PodcastFeedService polls every such feed every 6
hours (and once at startup), downloads any episode not already on disk using
the existing YYYYMMDD - Title.ext convention, and triggers the same
rescan-and-broadcast sequence "Bibliothek neu einlesen" already uses - now
shared via App.rescan_library() instead of duplicated. A show with no
feed.txt is untouched, so there is no new config section for this.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

python-backend/tests/test_podcast_service.py

@@ -0,0 +1,87 @@
+"""The podcast poll loop itself: cadence, error resilience, and client lifecycle."""
+
+from __future__ import annotations
+
+import asyncio
+from pathlib import Path
+
+import httpx2
+import pytest
+
+import musicmouse.services.podcasts as podcasts_module
+from musicmouse.services.podcasts import PodcastFeedService
+
+
+class _FakeLibrary:
+    def __init__(self, root: Path) -> None:
+        self.root = root
+
+
+async def _run_briefly(service: PodcastFeedService) -> None:
+    """Let `run()` complete a few fast-interval passes, then cancel it like shutdown does."""
+    task = asyncio.create_task(service.run())
+    await asyncio.sleep(0.05)
+    task.cancel()
+    with pytest.raises(asyncio.CancelledError):
+        await task
+
+
+@pytest.mark.asyncio
+async def test_run_checks_immediately_and_calls_on_change_only_when_something_changed(
+    tmp_path: Path, monkeypatch: pytest.MonkeyPatch
+) -> None:
+    calls = 0
+
+    async def fake_sync_all_shows(client: httpx2.AsyncClient, root: Path) -> bool:
+        nonlocal calls
+        calls += 1
+        return calls == 1  # only the very first pass finds something new
+
+    monkeypatch.setattr(podcasts_module, "sync_all_shows", fake_sync_all_shows)
+
+    changes = 0
+
+    async def on_change() -> None:
+        nonlocal changes
+        changes += 1
+
+    client = httpx2.AsyncClient(transport=httpx2.MockTransport(lambda _r: httpx2.Response(200)))
+    service = PodcastFeedService(
+        _FakeLibrary(tmp_path), client=client, on_change=on_change, interval=0.01
+    )
+
+    await _run_briefly(service)
+
+    assert changes == 1
+    assert calls >= 2
+    assert client.is_closed
+
+
+@pytest.mark.asyncio
+async def test_run_survives_a_failing_pass(
+    tmp_path: Path, monkeypatch: pytest.MonkeyPatch
+) -> None:
+    calls = 0
+
+    async def fake_sync_all_shows(client: httpx2.AsyncClient, root: Path) -> bool:
+        nonlocal calls
+        calls += 1
+        if calls == 1:
+            raise RuntimeError("boom")
+        return False
+
+    monkeypatch.setattr(podcasts_module, "sync_all_shows", fake_sync_all_shows)
+
+    async def on_change() -> None:
+        pytest.fail("on_change must not run when nothing changed")
+
+    client = httpx2.AsyncClient(transport=httpx2.MockTransport(lambda _r: httpx2.Response(200)))
+    service = PodcastFeedService(
+        _FakeLibrary(tmp_path), client=client, on_change=on_change, interval=0.01
+    )
+
+    await _run_briefly(service)
+
+    # The RuntimeError from the first pass must not have ended the loop.
+    assert calls >= 2
+    assert client.is_closed