test(be): every dependency override goes through override_dep

22 test files set `app.dependency_overrides[...]` by hand and tore down with a blanket `.clear()`
in a `finally`, which wipes every override rather than the test's own and stops fixtures composing.
They now take the `override_dep` fixture (helpers get it passed in), whose teardown restores each
key's prior value; no clear() carried meaning between two phases of a test. A convention test fails
any test file that writes `dependency_overrides` directly.

backend/tests/test_plex_discover.py

@@ -120,24 +120,21 @@ def _seed(db):
     return user
 
 
-def _get(db, user, monkeypatch, path):
+def _get(db, user, monkeypatch, override_dep, path):
     monkeypatch.setattr(state, "_configured_cache", True)
-    app.dependency_overrides[get_db] = lambda: db
-    app.dependency_overrides[current_user] = lambda: user
-    try:
-        client = TestClient(app)  # no context manager: skip lifespan
-        return client.get(path)
-    finally:
-        app.dependency_overrides.clear()
+    override_dep(get_db, lambda: db)
+    override_dep(current_user, lambda: user)
+    client = TestClient(app)  # no context manager: skip lifespan
+    return client.get(path)
 
 
 def _ids(cards):
     return [c["id"] for c in cards]
 
 
-def test_discover_shape_and_recently_added_order(db, monkeypatch):
+def test_discover_shape_and_recently_added_order(db, monkeypatch, override_dep):
     user = _seed(db)
-    resp = _get(db, user, monkeypatch, "/api/plex/discover?scope=both")
+    resp = _get(db, user, monkeypatch, override_dep, "/api/plex/discover?scope=both")
     assert resp.status_code == 200, resp.text
     d = resp.json()
     assert set(d) >= {"continue_watching", "recently_added", "genres", "because_you_watched"}
@@ -148,19 +145,19 @@ def test_discover_shape_and_recently_added_order(db, monkeypatch):
     assert genres.get("Drama") == 2 and genres.get("Comedy") == 1
 
 
-def test_genre_tiles_carry_poster_art(db, monkeypatch):
+def test_genre_tiles_carry_poster_art(db, monkeypatch, override_dep):
     # Each genre tile carries up to 4 poster rating_keys for the 2×2 collage (top_art_keys): the top
     # movies in that genre, best-rated then newest. No ratings here → newest-first; shows are excluded.
     user = _seed(db)
-    d = _get(db, user, monkeypatch, "/api/plex/discover?scope=both").json()
+    d = _get(db, user, monkeypatch, override_dep, "/api/plex/discover?scope=both").json()
     art = {g["value"]: g["art"] for g in d["genres"]}
     assert art["Drama"] == ["m1", "m3"]  # both Drama movies, m1 (newer) first
     assert art["Comedy"] == ["m2"]
 
 
-def test_continue_watching_movies_and_shows(db, monkeypatch):
+def test_continue_watching_movies_and_shows(db, monkeypatch, override_dep):
     user = _seed(db)
-    d = _get(db, user, monkeypatch, "/api/plex/discover?scope=both").json()
+    d = _get(db, user, monkeypatch, override_dep, "/api/plex/discover?scope=both").json()
     ids = _ids(d["continue_watching"])
     # The in-progress movie and the show with an in-progress episode are both present; the watched
     # anchor movie (m1) is not. Order is most-recently-progressed first (the show's ep beats m3).
@@ -168,7 +165,7 @@ def test_continue_watching_movies_and_shows(db, monkeypatch):
     assert "m1" not in ids
 
 
-def test_continue_watching_null_status_in_hidden_out(db, monkeypatch):
+def test_continue_watching_null_status_in_hidden_out(db, monkeypatch, override_dep):
     # A started movie whose PlexState.status is NULL is still "in progress": `NULL NOT IN (...)` is NULL
     # (not TRUE), so a bare notin_ would wrongly drop it — the or_(is_(None), notin_) branch keeps it.
     # A hidden started movie must be excluded.
@@ -207,13 +204,15 @@ def test_continue_watching_null_status_in_hidden_out(db, monkeypatch):
     db.commit()
 
     ids = _ids(
-        _get(db, user, monkeypatch, "/api/plex/discover?scope=movie").json()["continue_watching"]
+        _get(db, user, monkeypatch, override_dep, "/api/plex/discover?scope=movie").json()[
+            "continue_watching"
+        ]
     )
     assert "mn" in ids  # NULL-status started movie IS in progress
     assert "mh" not in ids  # hidden is excluded
 
 
-def test_continue_watching_excludes_fully_watched_show(db, monkeypatch):
+def test_continue_watching_excludes_fully_watched_show(db, monkeypatch, override_dep):
     # A show whose every episode is watched is DONE, not in-progress: the `watched < total` guard must
     # keep it off the Continue-watching rail (a bare `watched > 0` would wrongly resurface it).
     lib_s = PlexLibrary(plex_key="2", title="Shows", kind="show", enabled=True)
@@ -248,14 +247,16 @@ def test_continue_watching_excludes_fully_watched_show(db, monkeypatch):
     db.commit()
 
     ids = _ids(
-        _get(db, user, monkeypatch, "/api/plex/discover?scope=show").json()["continue_watching"]
+        _get(db, user, monkeypatch, override_dep, "/api/plex/discover?scope=show").json()[
+            "continue_watching"
+        ]
     )
     assert "shw" not in ids  # fully watched → excluded from continue-watching
 
 
-def test_because_you_watched_resolves_in_library_recs(db, monkeypatch):
+def test_because_you_watched_resolves_in_library_recs(db, monkeypatch, override_dep):
     user = _seed(db)
-    d = _get(db, user, monkeypatch, "/api/plex/discover?scope=both").json()
+    d = _get(db, user, monkeypatch, override_dep, "/api/plex/discover?scope=both").json()
     bw = d["because_you_watched"]
     assert bw is not None
     assert bw["anchor"]["id"] == "m1" and bw["anchor"]["title"] == "Anchor Movie"
@@ -263,34 +264,36 @@ def test_because_you_watched_resolves_in_library_recs(db, monkeypatch):
     assert _ids(bw["items"]) == ["m2"]
 
 
-def test_because_you_watched_null_without_history(db, monkeypatch):
+def test_because_you_watched_null_without_history(db, monkeypatch, override_dep):
     _seed(db)
     fresh = User(email="fresh-discover@example.com")
     db.add(fresh)
     db.commit()
-    d = _get(db, fresh, monkeypatch, "/api/plex/discover?scope=both").json()
+    d = _get(db, fresh, monkeypatch, override_dep, "/api/plex/discover?scope=both").json()
     # A user with no watched-and-enriched movie gets no recommendation rail.
     assert d["because_you_watched"] is None
     assert d["continue_watching"] == []
 
 
-def test_surprise_scope_and_bound(db, monkeypatch):
+def test_surprise_scope_and_bound(db, monkeypatch, override_dep):
     user = _seed(db)
-    resp = _get(db, user, monkeypatch, "/api/plex/surprise?scope=movie&limit=2")
+    resp = _get(db, user, monkeypatch, override_dep, "/api/plex/surprise?scope=movie&limit=2")
     assert resp.status_code == 200, resp.text
     items = resp.json()["items"]
     assert len(items) <= 2
     assert all(c["type"] == "movie" for c in items)  # scope=movie excludes shows
 
 
-def test_recently_watched_movies_and_episodes(db, monkeypatch):
+def test_recently_watched_movies_and_episodes(db, monkeypatch, override_dep):
     # The rail lists last-fully-watched titles newest-first: a watched MOVIE as its own card, a show as
     # the specific watched EPISODE (with its show title). _seed watches m1 (movie); add a watched episode.
     user = _seed(db)
     ep2 = db.execute(select(PlexItem).where(PlexItem.rating_key == "sh1e2")).scalars().one()
     db.add(PlexState(user_id=user.id, item_id=ep2.id, status="watched", watched_at=NOW))
     db.commit()
-    rw = _get(db, user, monkeypatch, "/api/plex/discover?scope=both").json()["recently_watched"]
+    rw = _get(db, user, monkeypatch, override_dep, "/api/plex/discover?scope=both").json()[
+        "recently_watched"
+    ]
     by_id = {c["id"]: c for c in rw}
     assert "m1" in by_id and by_id["m1"]["type"] == "movie"
     assert "sh1e2" in by_id and by_id["sh1e2"]["type"] == "episode"
@@ -299,11 +302,13 @@ def test_recently_watched_movies_and_episodes(db, monkeypatch):
     assert set(_ids(rw)) == {"m1", "sh1e2"}
 
 
-def test_surprise_excludes_watched_and_caps_per_kind(db, monkeypatch):
+def test_surprise_excludes_watched_and_caps_per_kind(db, monkeypatch, override_dep):
     # Surprise surfaces only UNSEEN titles: the watched movie (m1) is out; the unwatched (m2), the
     # in-progress movie (m3) and the partially-watched show (sh1) are eligible. Capped at 3 per kind.
     user = _seed(db)
-    items = _get(db, user, monkeypatch, "/api/plex/surprise?scope=both").json()["items"]
+    items = _get(db, user, monkeypatch, override_dep, "/api/plex/surprise?scope=both").json()[
+        "items"
+    ]
     ids = _ids(items)
     assert "m1" not in ids  # watched → excluded
     assert set(ids) <= {"m2", "m3", "sh1"}  # only unseen titles
@@ -311,19 +316,21 @@ def test_surprise_excludes_watched_and_caps_per_kind(db, monkeypatch):
     assert len([c for c in items if c["type"] == "show"]) <= 3
 
 
-def test_discover_scope_movie_excludes_shows(db, monkeypatch):
+def test_discover_scope_movie_excludes_shows(db, monkeypatch, override_dep):
     user = _seed(db)
-    d = _get(db, user, monkeypatch, "/api/plex/discover?scope=movie").json()
+    d = _get(db, user, monkeypatch, override_dep, "/api/plex/discover?scope=movie").json()
     assert all(c["type"] == "movie" for c in d["recently_added"])
     # The show drops out of continue watching under the movie scope.
     assert _ids(d["continue_watching"]) == ["m3"]
 
 
-def test_filters_narrow_every_discover_rail(db, monkeypatch):
+def test_filters_narrow_every_discover_rail(db, monkeypatch, override_dep):
     # The sidebar filters constrain the Discover rails just like the Browse grid (ask 3). A genre=Drama
     # filter keeps only the Drama titles across every rail; the genre-less show and the Comedy rec drop.
     user = _seed(db)
-    d = _get(db, user, monkeypatch, "/api/plex/discover?scope=both&genres=Drama").json()
+    d = _get(
+        db, user, monkeypatch, override_dep, "/api/plex/discover?scope=both&genres=Drama"
+    ).json()
     # Recently-added: m1 + m3 (Drama) survive; Comedy m2 and the genre-less show sh1 are filtered out.
     assert set(_ids(d["recently_added"])) == {"m1", "m3"}
     # Continue-watching: only the in-progress Drama movie remains (the show has no genres → excluded).
@@ -334,10 +341,10 @@ def test_filters_narrow_every_discover_rail(db, monkeypatch):
     assert d["because_you_watched"] is None
 
 
-def test_filters_narrow_surprise(db, monkeypatch):
+def test_filters_narrow_surprise(db, monkeypatch, override_dep):
     user = _seed(db)
-    items = _get(db, user, monkeypatch, "/api/plex/surprise?scope=movie&genres=Comedy").json()[
-        "items"
-    ]
+    items = _get(
+        db, user, monkeypatch, override_dep, "/api/plex/surprise?scope=movie&genres=Comedy"
+    ).json()["items"]
     # Only the one Comedy movie qualifies under the filter.
     assert _ids(items) == ["m2"]