fix: persist all found candidates and guard duplicate adapter names

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

worker/tests/test_pipeline.py

@@ -99,3 +99,32 @@ def test_dedupe_skips_already_in_library(conn):
         cur.execute('SELECT count(*) FROM "LibraryItem" WHERE artist = %s AND album = %s',
                     ("Radiohead", "In Rainbows"))
         assert cur.fetchone()[0] == 1  # not duplicated
+
+
+def test_below_threshold_candidates_are_persisted_for_diagnosis(conn):
+    from lyra_worker.adapters.fakes import FakeQobuz
+    from lyra_worker.types import MBTarget
+
+    class WrongAlbumQobuz(FakeQobuz):
+        def search(self, target):
+            # returns a candidate for a different album -> scores below the gate
+            return super().search(MBTarget(artist=target.artist, album="Some Completely Unrelated Title"))
+
+    job_id = insert_request(conn, artist="Radiohead", album="In Rainbows")
+    claim_next(conn)
+    run_pipeline(conn, job_id, [WrongAlbumQobuz()], dest_root="/tmp/lib")
+
+    assert _job_state(conn, job_id)[0] == "needs_attention"
+    with conn.cursor() as cur:
+        cur.execute('SELECT count(*) FROM "Candidate" WHERE "jobId" = %s', (job_id,))
+        assert cur.fetchone()[0] >= 1  # found-but-rejected candidate retained for diagnosis
+
+
+def test_duplicate_adapter_names_raise(conn):
+    import pytest
+    from lyra_worker.adapters.fakes import FakeQobuz
+
+    job_id = insert_request(conn, artist="Radiohead", album="In Rainbows")
+    claim_next(conn)
+    with pytest.raises(ValueError):
+        run_pipeline(conn, job_id, [FakeQobuz(), FakeQobuz()], dest_root="/tmp/lib")