fix(matching): preserve remix intent in collect preview + strengthen tie test (#551)

CodeRabbit review on #553:
- collect enrich-preview called find_best_match with the default prefer_original=
  True, so a named-remix query (e.g. "Surrender (Hardstyle Remix)") would favour
  the original version's BPM/key. Derive prefer_original from the title via
  is_remix_title, matching the enrichment pipeline and recommendation paths — the
  consistency #551 is about. Pinned with a regression test that asserts the
  computed prefer_original for a remix vs a plain query.
- Strengthen the disabled-preference tie test to assert the deterministic winner
  (track_id "1") instead of just non-None.

Closes #551

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Author: thewrz

server/app/api/collect.py

@@ -57,7 +57,7 @@
 from app.services.system_settings import get_system_settings
 from app.services.tidal import sync_collection_requests_batch
 from app.services.track_match import find_best_match
-from app.services.track_normalizer import normalize_isrc
+from app.services.track_normalizer import is_remix_title, normalize_isrc
 from app.services.vote import add_vote
 
 logger = logging.getLogger(__name__)
@@ -563,7 +563,14 @@ def enrich_preview(
             try:
                 matches = search_beatport_tracks(db, user, f"{item.artist} {item.title}", limit=5)
                 if matches:
-                    best = find_best_match(matches, item.title, item.artist)
+                    # Preserve remix intent like the enrichment/recommendation paths:
+                    # only prefer the original version when the query isn't a named remix.
+                    best = find_best_match(
+                        matches,
+                        item.title,
+                        item.artist,
+                        prefer_original=not is_remix_title(item.title),
+                    )
                     if best:
                         bpm = int(best.bpm) if best.bpm is not None else None
                         key = best.key or None

server/tests/test_collect_public.py

@@ -1014,6 +1014,40 @@ def test_enrich_preview_returns_bpm_from_beatport(client, db, test_event: Event)
     assert results[0]["genre"] == "Progressive House"
 
 
+def test_enrich_preview_preserves_remix_intent(client, db, test_event: Event):
+    """The preview must derive prefer_original from the title (#551/#553): a named-remix
+    query must NOT be matched with prefer_original=True (which would favour the original
+    version's BPM/key), matching the enrichment + recommendation paths."""
+    from unittest.mock import MagicMock, patch
+
+    _enable_collection(db, test_event)
+    dj = test_event.created_by
+    dj.beatport_access_token = "fake_token"  # nosec B106
+    db.commit()
+
+    match = MagicMock(
+        title="Surrender (Hardstyle Remix)", artist="Darude", bpm=165, key=None, genre=None
+    )
+    with (
+        patch("app.api.collect.search_beatport_tracks", return_value=[match]),
+        patch("app.api.collect.find_best_match", return_value=match) as spy,
+    ):
+        # Remix query → prefer_original must be False.
+        client.post(
+            f"/api/public/collect/{test_event.code}/enrich-preview",
+            json={"items": [{"title": "Surrender (Hardstyle Remix)", "artist": "Darude"}]},
+        )
+        assert spy.call_args.kwargs["prefer_original"] is False
+
+        # Plain query → prefer_original stays True.
+        spy.reset_mock()
+        client.post(
+            f"/api/public/collect/{test_event.code}/enrich-preview",
+            json={"items": [{"title": "Surrender", "artist": "Darude"}]},
+        )
+        assert spy.call_args.kwargs["prefer_original"] is True
+
+
 def test_enrich_preview_caps_at_10_items(client, db, test_event: Event):
     """Requests with >10 items are silently capped — only first 10 processed."""
     _enable_collection(db, test_event)

server/tests/test_track_match.py

@@ -92,9 +92,10 @@ def test_remix_preferred_when_disabled(self):
                 track_id="2", title="Surrender", artist="Darude", mix_name="Original Mix", bpm=132
             ),
         ]
-        # No version bonus/penalty → first encountered wins on an otherwise-exact tie.
+        # With the original-mix bonus disabled the remix (first result) is no longer
+        # demoted, so it wins the otherwise-exact tie instead of the Original Mix.
         best = find_best_match(results, "Surrender", "Darude", prefer_original=False)
-        assert best is not None
+        assert best.track_id == "1"
 
     def test_tidal_remix_title_penalized(self):
         results = [