Split shorts from regular videos with a vertical shorts feed

- Detect shorts by duration (SHORTS_MAX_DURATION_SECONDS, default 180)
  and expose is_short in feed, video and channel-activity DTOs.
- Feed gains type=all|long|short and anchor; lists show a two-mode
  'Обычные | Shorts' filter (no 'Все') persisted in the URL.
- Clicking a short opens /shorts/🆔 a vertical scroll-snap feed with
  autoplay for the active slide, context-aware endpoints and infinite
  loading.
- Keep the sound choice across swipes, syncing with the player's own
  mute control and guarding against the widget's stale isMuted() reads.

tests/test_shorts_feed.py

@@ -0,0 +1,171 @@
+"""Tests for the Shorts/long split on /api/feed: the `type` filter, the
+`is_short` flag and the one-off `anchor` starting point (see
+analytics/2026-09-27-shorts-split-and-feed.md)."""
+
+from datetime import datetime, timedelta, timezone
+
+import pytest
+from fastapi.testclient import TestClient
+
+from app.core.auth_dependency import require_session
+from app.db import get_db
+from app.main import app
+from app.models.channel import Channel
+from app.models.video import Video
+
+
+@pytest.fixture
+def client(db_session):
+    def _get_db_override():
+        yield db_session
+
+    app.dependency_overrides[get_db] = _get_db_override
+    app.dependency_overrides[require_session] = lambda: None
+    # Deliberately not using `with TestClient(app)`: that runs the app's
+    # lifespan, which would try to reach the real MeTube instance and DB.
+    yield TestClient(app)
+    del app.dependency_overrides[get_db]
+    del app.dependency_overrides[require_session]
+
+
+BASE = datetime(2026, 9, 10, tzinfo=timezone.utc)
+
+# Insertion order gives increasing ids. published_at also increases with i,
+# so the descending feed order is v4, v3, v2, v1, v0.
+DURATIONS = {
+    "v0": None,  # unknown -> long
+    "v1": 179,  # short
+    "v2": 180,  # short (boundary, inclusive)
+    "v3": 181,  # long (just above the threshold)
+    "v4": 100,  # short
+}
+
+
+def _seed(db_session):
+    channel = Channel(youtube_channel_id="chanShorts", title="Channel Shorts", subscribed=True)
+    db_session.add(channel)
+    db_session.commit()
+
+    videos = []
+    for i, (youtube_video_id, duration) in enumerate(DURATIONS.items()):
+        video = Video(
+            youtube_video_id=youtube_video_id,
+            channel_id=channel.id,
+            title=f"Video {youtube_video_id}",
+            published_at=BASE + timedelta(hours=i),
+            duration_seconds=duration,
+            youtube_url=f"https://www.youtube.com/watch?v={youtube_video_id}",
+        )
+        videos.append(video)
+    db_session.add_all(videos)
+    db_session.commit()
+    return channel, videos
+
+
+def _ids(resp):
+    return [item["youtube_video_id"] for item in resp["items"]]
+
+
+def test_feed_type_short_only_includes_at_or_below_threshold(client, db_session):
+    _seed(db_session)
+
+    assert _ids(client.get("/api/feed?type=short").json()) == ["v4", "v2", "v1"]
+
+
+def test_feed_type_long_includes_null_and_above_threshold(client, db_session):
+    _seed(db_session)
+
+    assert _ids(client.get("/api/feed?type=long").json()) == ["v3", "v0"]
+
+
+def test_feed_type_all_matches_default(client, db_session):
+    _seed(db_session)
+
+    explicit = client.get("/api/feed?type=all").json()
+    default = client.get("/api/feed").json()
+    assert _ids(explicit) == ["v4", "v3", "v2", "v1", "v0"]
+    assert explicit["items"] == default["items"]
+
+
+def test_feed_type_invalid_returns_422(client, db_session):
+    _seed(db_session)
+
+    assert client.get("/api/feed?type=weird").status_code == 422
+
+
+def test_feed_type_threshold_is_configurable(client, db_session, monkeypatch):
+    _seed(db_session)
+
+    monkeypatch.setattr("app.config.settings.shorts_max_duration_seconds", 181)
+
+    assert set(_ids(client.get("/api/feed?type=short").json())) == {"v4", "v3", "v2", "v1"}
+    assert _ids(client.get("/api/feed?type=long").json()) == ["v0"]
+
+
+def test_feed_item_is_short_flag(client, db_session):
+    _seed(db_session)
+
+    items = {item["youtube_video_id"]: item for item in client.get("/api/feed").json()["items"]}
+
+    assert items["v1"]["is_short"] is True
+    assert items["v2"]["is_short"] is True
+    assert items["v4"]["is_short"] is True
+    assert items["v3"]["is_short"] is False
+    assert items["v0"]["is_short"] is False
+
+
+def test_feed_type_short_pagination_in_filtered_set(client, db_session):
+    _seed(db_session)
+
+    page1 = client.get("/api/feed?type=short&limit=2").json()
+    assert _ids(page1) == ["v4", "v2"]
+    assert page1["next_cursor"] is not None
+
+    page2 = client.get(f"/api/feed?type=short&limit=2&cursor={page1['next_cursor']}").json()
+    assert _ids(page2) == ["v1"]
+    assert page2["next_cursor"] is None
+
+
+def test_feed_type_long_pagination_in_filtered_set(client, db_session):
+    _seed(db_session)
+
+    page1 = client.get("/api/feed?type=long&limit=1").json()
+    assert _ids(page1) == ["v3"]
+    assert page1["next_cursor"] is not None
+
+    page2 = client.get(f"/api/feed?type=long&limit=1&cursor={page1['next_cursor']}").json()
+    assert _ids(page2) == ["v0"]
+    assert page2["next_cursor"] is None
+
+
+def test_feed_anchor_starts_at_video_and_goes_older(client, db_session):
+    _seed(db_session)
+
+    assert _ids(client.get("/api/feed?anchor=v2").json()) == ["v2", "v1", "v0"]
+
+
+def test_feed_anchor_unknown_falls_back_to_first_page(client, db_session):
+    _seed(db_session)
+
+    resp = client.get("/api/feed?anchor=does-not-exist").json()
+    assert _ids(resp) == ["v4", "v3", "v2", "v1", "v0"]
+
+
+def test_feed_anchor_ignored_when_cursor_present(client, db_session):
+    _seed(db_session)
+
+    page1 = client.get("/api/feed?anchor=v2&limit=2").json()
+    assert _ids(page1) == ["v2", "v1"]
+    assert page1["next_cursor"] is not None
+
+    # A (different) anchor on a cursor page must not shift the selection:
+    # only the first page uses the anchor.
+    page2 = client.get(f"/api/feed?anchor=v4&cursor={page1['next_cursor']}").json()
+    assert _ids(page2) == ["v0"]
+
+
+def test_feed_anchor_combines_with_type_filter(client, db_session):
+    _seed(db_session)
+
+    assert client.get("/api/feed?type=short&anchor=v0").json()["items"] == []
+    assert _ids(client.get("/api/feed?type=short&anchor=v3").json()) == ["v2", "v1"]