feat(node,hub): add Videos group app (poster grid, flat list, TMDB metadata)

Implements docs/mediacenter.md: a "Videos" group application built on the
existing files index rather than a separate catalogue. On the node side,
new indexer enrichment (technical probe, filename/season parsing, thumbnail
generation) runs per-file once an operator has chosen a video_root for the
group, plus a TMDB client for on-demand poster/metadata lookups (never
client-side, thumbnails delivered over the existing chunk path). On the hub
side, a new video-app.js renders a lazily-mounted poster grid or a
thumbnail-only flat list, with TMDB entirely optional per group.

Along the way: the global apps registry now drives Settings' default-tab
picker instead of a hardcoded list, and the video_root is configured from
group Settings (like uploads) rather than from Files, with the node
refusing to run any TMDB/thumbnail work until one is set.

Fixes several bugs found via live testing against a real library, notably
a race between two effects writing the same "image ready" state that could
leave a poster grid spinning forever on a same-tab revisit — see
mediacenter.md §5.4 for the full account of each one.

1 files changed, 88 insertions, 0 deletions

diff --git a/packages/meshbay-node/tests/test_poster_cache.py b/packages/meshbay-node/tests/test_poster_cache.py
new file mode 100644
index 0000000..bbd824d
--- /dev/null
+++ b/packages/meshbay-node/tests/test_poster_cache.py
@@ -0,0 +1,88 @@
+"""
+Bug found live, 2026-08-24: `_fetch_and_cache_poster` downloaded a TMDB
+poster/backdrop from `image.tmdb.org` on *every* `media_meta_req`, even for
+a file whose TMDB match was already cached — the content-addressed
+`thumb_hash` isn't known until the bytes are downloaded, so nothing had
+ever checked "have I already fetched this poster_path" first. On a group
+with a show split across release folders (§V6), one Videos-tab visit
+triggered four to six redundant image downloads; compounded with TMDB
+latency (or a stall), this is what an operator saw as posters that "never
+finish loading" on a second visit.
+
+Fixed by keying the `thumbs` cache by a synthetic `tmdb:{poster_path}` id
+*before* the network call, mirroring the `file_id` convention `_do_file_request`
+already uses to resolve a thumbnail by id.
+"""
+
+import pytest
+
+from meshbay_node.media_cache import MediaCache
+from meshbay_node.transport.webrtc_server import WebRTCPeerSession
+
+pytestmark = pytest.mark.asyncio
+
+
+@pytest.fixture
+async def media_cache(tmp_path):
+    c = MediaCache(db_path=tmp_path / "media_cache.db")
+    await c.open()
+    yield c
+    await c.close()
+
+
+class FakeTmdbClient:
+    def __init__(self):
+        self.fetch_calls = 0
+
+    @staticmethod
+    def poster_url(path):
+        return f"https://image.tmdb.org/t/p/w500{path}"
+
+    async def fetch_image(self, url):
+        self.fetch_calls += 1
+        return b"jpeg-bytes-for-" + url.encode()
+
+
+async def test_second_fetch_for_the_same_poster_path_skips_the_network(media_cache):
+    client = FakeTmdbClient()
+
+    first = await WebRTCPeerSession._fetch_and_cache_poster(
+        media_cache, client, "/poster.jpg")
+    second = await WebRTCPeerSession._fetch_and_cache_poster(
+        media_cache, client, "/poster.jpg")
+
+    assert first == second, "the same poster_path must yield the same thumb_hash"
+    assert client.fetch_calls == 1, (
+        "a poster already cached must never be re-downloaded from TMDB")
+
+
+async def test_different_poster_paths_are_each_fetched_once(media_cache):
+    client = FakeTmdbClient()
+
+    poster_hash = await WebRTCPeerSession._fetch_and_cache_poster(
+        media_cache, client, "/poster.jpg")
+    backdrop_hash = await WebRTCPeerSession._fetch_and_cache_poster(
+        media_cache, client, "/backdrop.jpg")
+    poster_hash_again = await WebRTCPeerSession._fetch_and_cache_poster(
+        media_cache, client, "/poster.jpg")
+
+    assert poster_hash != backdrop_hash
+    assert poster_hash == poster_hash_again
+    assert client.fetch_calls == 2, "one network fetch per distinct poster_path"
+
+
+async def test_none_path_is_a_no_op(media_cache):
+    client = FakeTmdbClient()
+    result = await WebRTCPeerSession._fetch_and_cache_poster(media_cache, client, None)
+    assert result is None
+    assert client.fetch_calls == 0
+
+
+async def test_cached_hash_actually_serves_the_downloaded_bytes(media_cache):
+    client = FakeTmdbClient()
+    thumb_hash = await WebRTCPeerSession._fetch_and_cache_poster(
+        media_cache, client, "/poster.jpg")
+    await WebRTCPeerSession._fetch_and_cache_poster(media_cache, client, "/poster.jpg")
+
+    stored = await media_cache.get_thumb(thumb_hash)
+    assert stored == b"jpeg-bytes-for-https://image.tmdb.org/t/p/w500/poster.jpg"