fix(plex): re-probe on file replace, HU parity, public class const, playback-class test gaps

Deep-review round 1 on feature/plex-playback-class-filter:

- Sticky watermark (medium): _apply_item reset the bit-depth probe watermark
  only on a codec-string change, so a same-codec re-encode (8-bit->10-bit HEVC)
  kept a stale video_bit_depth/transcode_hw forever (the backfill only re-probes
  media_probed_at IS NULL rows). Also reset when the Plex Part key changes (the
  file was replaced), not just the codec.

- i18n parity (medium): the HU playback-class labels were mixed-language (only
  'direct' translated). Translated remux/transcode_hw/transcode_sw and the
  tooltips consistently to Hungarian (Kozvetlen streameles / Atkodolas).

- Layering (low): _PLAYBACK_CLASSES was module-private yet imported across into
  routes.plex.browse; renamed to public PLAYBACK_CLASSES (it is the shared
  source of truth for facet order + zero-fill).

- a11y (low): the browse-card playback-class dot conveyed meaning only via a
  mouse-hover title; added role=img + aria-label so SR/touch users get the class.

- tests: the NULL/unprobed transcode_hw -> SW fold (filter + facet), facet
  self-exclusion under an active playable filter, the migration codec-set ==
  HW_DECODABLE_CODECS drift guard, the probe-batch bound + oldest-first order,
  the transient probe-failure retry path, and the same-codec re-encode re-probe.

Backend gate green (ruff + full pytest); FE gate green (tsc/lint/knip/prettier/
vitest). NOTE: the facet-vs-runtime disagreement for 10-bit HEVC (C1) is the
known merge-order constraint — this branch's runtime is codec-only; the facet
becomes truthful once BUG1/tonemap's bit-depth-aware routing lands with it. Left
as a sequencing constraint, not code-changed here.

backend/tests/test_plex_playback_class.py

@@ -7,6 +7,9 @@ backfill). These tests pin that a 10-bit/HDR HEVC lands in SW even though its co
 the exact case the runtime VAAPI path (plex.stream) also special-cases.
 """
 
+import re
+from pathlib import Path
+
 import app.state as state
 from app.auth import current_user
 from app.db import get_db
@@ -70,8 +73,11 @@ class TestSyncDerivation:
     """`_apply_item` sets transcode_hw codec-only at sync (bit depth unknown from the listing), and a
     changed video codec resets the probe watermark so a stale bit-depth can't linger."""
 
-    def _meta(self, vcodec):
-        return {"title": "X", "Media": [{"videoCodec": vcodec, "Part": [{"file": "/m.mkv"}]}]}
+    def _meta(self, vcodec, *, key="/parts/1/file.mkv", file="/m.mkv"):
+        return {
+            "title": "X",
+            "Media": [{"videoCodec": vcodec, "Part": [{"file": file, "key": key}]}],
+        }
 
     def test_codec_only_derivation_at_sync(self):
         row = PlexItem(rating_key="x", kind="movie")
@@ -102,6 +108,37 @@ class TestSyncDerivation:
         sync._apply_item(row, lib_id=1, kind="movie", meta=self._meta("h264"))
         assert row.video_bit_depth is None and row.media_probed_at is None
 
+    def test_same_codec_reencode_with_a_new_part_resets_the_probe(self):
+        # A same-codec bit-depth re-encode (e.g. 8-bit→10-bit HEVC) keeps codec 'hevc' but replaces the
+        # physical file, so its Plex Part key changes. Codec-only reset would miss this and keep the stale
+        # 8-bit/HW verdict forever (the backfill only re-probes media_probed_at IS NULL rows) — the
+        # part-key move must reset the watermark so the new bit depth is re-probed.
+        row = PlexItem(rating_key="x", kind="movie")
+        sync._apply_item(row, lib_id=1, kind="movie", meta=self._meta("hevc", key="/parts/1/f.mkv"))
+        row.transcode_hw = True
+        row.video_bit_depth = 8
+        row.media_probed_at = sync.datetime.now(sync.timezone.utc)
+        # Re-encoded in place: same codec 'hevc', but a new Part key (new file).
+        sync._apply_item(row, lib_id=1, kind="movie", meta=self._meta("hevc", key="/parts/2/f.mkv"))
+        assert row.video_bit_depth is None and row.media_probed_at is None  # re-probe scheduled
+
+
+def test_migration_codec_set_matches_hw_decodable_codecs():
+    # Migration 0077 hardcodes the HW-decodable codec set in raw SQL and its comment mandates it stay
+    # identical to plex.sync.HW_DECODABLE_CODECS. A comment isn't enforcement (house rule) — pin the
+    # equality so adding/removing a codec from the frozenset without editing the migration fails here
+    # (else already-migrated prod rows keep a wrong transcode_hw the runtime derivation wouldn't catch).
+    mig = (
+        Path(__file__).resolve().parent.parent
+        / "alembic"
+        / "versions"
+        / "0077_plex_playback_class.py"
+    )
+    m = re.search(r"lower\(codec_video\)\s+IN\s+\(([^)]*)\)", mig.read_text())
+    assert m, "could not find the codec IN(...) list in migration 0077"
+    codecs = {c.strip().strip("'\"").lower() for c in m.group(1).split(",")}
+    assert codecs == {c.lower() for c in sync.HW_DECODABLE_CODECS}
+
 
 class _FakePlex:
     """Stands in for PlexClient.metadata — returns a canned full-metadata dict per rating_key."""
@@ -188,6 +225,93 @@ def test_probe_stamps_even_when_plex_has_no_stream(db):
     assert item.transcode_hw is True
 
 
+def test_probe_media_batch_is_bounded_and_oldest_first(db):
+    # The per-run bound (limit) caps Plex load; oldest-id-first means successive runs cover the whole
+    # backlog without starving any item. Seed 3 eligible items, probe with limit=2.
+    lib = PlexLibrary(plex_key="1", title="Movies", kind="movie", enabled=True)
+    db.add(lib)
+    db.flush()
+    items = [
+        PlexItem(
+            rating_key=f"h{i}",
+            library_id=lib.id,
+            kind="movie",
+            title=f"m{i}",
+            playable="transcode",
+            codec_video="hevc",
+            transcode_hw=True,
+        )
+        for i in range(3)
+    ]
+    db.add_all(items)  # inserted in order → ascending ids
+    db.commit()
+    plex = _FakePlex(
+        {
+            f"h{i}": {"Media": [{"Part": [{"Stream": [{"streamType": 1, "bitDepth": 8}]}]}]}
+            for i in range(3)
+        }
+    )
+    assert sync._probe_media_batch(db, plex, limit=2) == 2  # exactly the bound
+    for it in items:
+        db.refresh(it)
+    # The two LOWEST-id rows were probed; the third waits for the next run.
+    assert items[0].media_probed_at is not None and items[1].media_probed_at is not None
+    assert items[2].media_probed_at is None
+    # The next run continues with the remaining item.
+    assert sync._probe_media_batch(db, plex, limit=2) == 1
+    db.refresh(items[2])
+    assert items[2].media_probed_at is not None
+
+
+class _RaisingPlex:
+    """metadata() raises for `bad_key`, returns a canned dict otherwise — to exercise the transient
+    fetch-failure branch (leave the watermark NULL so the item retries next run)."""
+
+    def __init__(self, by_key, bad_key):
+        self.by_key = by_key
+        self.bad_key = bad_key
+
+    def metadata(self, rating_key, markers=False):
+        if rating_key == self.bad_key:
+            raise RuntimeError("plex timeout")
+        return self.by_key.get(rating_key)
+
+
+def test_probe_media_batch_leaves_a_transient_failure_unstamped_to_retry(db):
+    lib = PlexLibrary(plex_key="1", title="Movies", kind="movie", enabled=True)
+    db.add(lib)
+    db.flush()
+    good = PlexItem(
+        rating_key="g",
+        library_id=lib.id,
+        kind="movie",
+        title="good",
+        playable="transcode",
+        codec_video="hevc",
+        transcode_hw=True,
+    )
+    bad = PlexItem(
+        rating_key="b",
+        library_id=lib.id,
+        kind="movie",
+        title="bad",
+        playable="transcode",
+        codec_video="hevc",
+        transcode_hw=True,
+    )
+    db.add_all([good, bad])
+    db.commit()
+    plex = _RaisingPlex(
+        {"g": {"Media": [{"Part": [{"Stream": [{"streamType": 1, "bitDepth": 10}]}]}]}}, bad_key="b"
+    )
+    # The raise on 'b' must not abort the batch: 'g' is still probed and counted; 'b' stays NULL.
+    assert sync._probe_media_batch(db, plex) == 1
+    db.refresh(good)
+    db.refresh(bad)
+    assert good.media_probed_at is not None and good.transcode_hw is False  # 10-bit → SW
+    assert bad.media_probed_at is None  # transient failure → retried next run, not stamped
+
+
 def _seed_classes(db):
     lib = PlexLibrary(plex_key="1", title="Movies", kind="movie", enabled=True)
     db.add(lib)
@@ -274,3 +398,56 @@ def test_facets_count_playback_classes_in_severity_order(db, monkeypatch):
         "transcode_hw": 1,
         "transcode_sw": 1,
     }
+
+
+def test_unprobed_transcode_folds_into_sw(db, monkeypatch):
+    # transcode_hw NULL is the COMMON initial state (before the bit-depth backfill runs). The query's
+    # CASE has no explicit NULL arm — it relies on the `playable=='transcode'` else folding NULL in with
+    # software. Pin that fold for BOTH the filter and the facet, so a reorder can't silently drop the
+    # item from the feed (an honest-state violation).
+    lib = PlexLibrary(plex_key="1", title="Movies", kind="movie", enabled=True)
+    db.add(lib)
+    db.flush()
+    db.add(
+        PlexItem(
+            rating_key="tnull",
+            library_id=lib.id,
+            kind="movie",
+            title="Unprobed",
+            playable="transcode",
+            codec_video="hevc",
+            transcode_hw=None,
+        )
+    )
+    user = User(email="pnull@example.com")
+    db.add(user)
+    db.commit()
+    client = _client(db, user, monkeypatch)
+    try:
+        sw = client.get("/api/plex/library?scope=movie&playable=transcode_sw")
+        assert {i["id"] for i in sw.json()["items"]} == {"tnull"}  # NULL → SW bucket
+        hw = client.get("/api/plex/library?scope=movie&playable=transcode_hw")
+        assert hw.json()["items"] == []  # never HW
+        facets = client.get("/api/plex/facets?scope=movie")
+        counts = {p["value"]: p["count"] for p in facets.json()["playable"]}
+        assert counts.get("transcode_sw") == 1 and counts.get("transcode_hw", 0) == 0
+    finally:
+        app.dependency_overrides.clear()
+
+
+def test_facet_playable_self_excludes_the_active_selection(db, monkeypatch):
+    # A selected playable class must NOT narrow the playable facet's OWN counts (facet self-exclusion),
+    # otherwise picking one class would collapse the list and you couldn't OR-add a second. Selecting
+    # 'direct' must still return all four classes at their full, unnarrowed counts.
+    _seed_classes(db)
+    user = User(email="pself@example.com")
+    db.add(user)
+    db.commit()
+    client = _client(db, user, monkeypatch)
+    try:
+        resp = client.get("/api/plex/facets?scope=movie&playable=direct")
+    finally:
+        app.dependency_overrides.clear()
+    assert resp.status_code == 200, resp.text
+    counts = {p["value"]: p["count"] for p in resp.json()["playable"]}
+    assert counts == {"direct": 1, "remux": 1, "transcode_hw": 1, "transcode_sw": 1}