feat(discovery): build_similarity_sources + worker sweep/trigger wiring

Adds registry.build_similarity_sources() (always constructs
ListenBrainzSource; reachability is a per-run health() concern, not a
startup gate) and wires discovery into the worker's main loop: a
scheduled sweep gated on discover.enabled + DISCOVER_TICK_SECONDS, and
a one-shot discover.requested trigger mirroring the existing
scan.requested pattern.

Also hardens run_discovery's health-check pass: a source whose
health() raises is now logged and skipped instead of aborting the
whole sweep (accepted finding from the Task-3 review).

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

worker/tests/test_discovery.py

@@ -72,6 +72,21 @@ def test_unhealthy_source_contributes_nothing(conn):
     assert _artist_rows(conn) == []
 
 
+def test_source_with_raising_health_is_skipped_not_fatal(conn):
+    insert_watched_artist(conn, mbid="s1", name="Seed")
+
+    class BoomSource:
+        name = "boom"
+        def health(self):
+            raise RuntimeError("boom")
+        def similar_artists(self, mbid):
+            return []
+
+    good = FakeSimilaritySource(similar={"s1": [SimilarArtist("c1", "X", 0.9)]})
+    result = run_discovery(conn, [BoomSource(), good], FakeMbBrowser(), DiscoveryConfig())
+    assert result.artists == 1  # good source still processed; boom skipped, no crash
+
+
 def test_config_from_config_parses_and_defaults():
     cfg = DiscoveryConfig.from_config({"discover.enabled": "true", "discover.maxSeeds": "10",
                                        "discover.minScore": "0.3"})

worker/tests/test_discovery_trigger.py

@@ -0,0 +1,35 @@
+from lyra_worker.adapters.fakes import FakeMbBrowser, FakeSimilaritySource
+from lyra_worker.main import _run_discovery
+from lyra_worker.similarity.base import SimilarArtist
+from tests.conftest import insert_watched_artist
+
+
+def _set(conn, key, value):
+    with conn.cursor() as cur:
+        cur.execute(
+            'INSERT INTO "Config"(key, value, secret, "updatedAt") VALUES (%s, %s, false, now()) '
+            'ON CONFLICT (key) DO UPDATE SET value = EXCLUDED.value, "updatedAt" = now()',
+            (key, value),
+        )
+    conn.commit()
+
+
+def _get(conn, key):
+    with conn.cursor() as cur:
+        cur.execute('SELECT value FROM "Config" WHERE key = %s', (key,))
+        row = cur.fetchone()
+        return row[0] if row else None
+
+
+def test_run_discovery_writes_result_and_clears_flag(conn):
+    insert_watched_artist(conn, mbid="s1", name="Seed")
+    _set(conn, "discover.requested", "true")
+    src = FakeSimilaritySource(similar={"s1": [SimilarArtist("c1", "Cand", 0.9)]})
+
+    _run_discovery(conn, [src], FakeMbBrowser())
+
+    assert _get(conn, "discover.requested") == "false"          # flag cleared
+    assert "artists" in (_get(conn, "discover.result") or "")   # summary written
+    with conn.cursor() as cur:
+        cur.execute('SELECT count(*) FROM "DiscoverySuggestion" WHERE kind = \'artist\'')
+        assert cur.fetchone()[0] == 1

worker/tests/test_similarity_registry.py

@@ -0,0 +1,14 @@
+from lyra_worker.registry import build_similarity_sources
+from lyra_worker.similarity._listenbrainz import ListenBrainzSource
+
+
+def test_build_returns_listenbrainz_by_default():
+    sources = build_similarity_sources({})
+    assert len(sources) == 1
+    assert isinstance(sources[0], ListenBrainzSource)
+    assert sources[0].name == "listenbrainz"
+
+
+def test_base_url_override_from_config():
+    src = build_similarity_sources({"discover.listenBrainzUrl": "http://lb.local"})[0]
+    assert src._base == "http://lb.local"