feat(fc3a): ArtistService.find_or_create + autocomplete

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

tests/test_artist_service_find_or_create.py

@@ -0,0 +1,56 @@
+import pytest
+
+from backend.app.models import Artist
+from backend.app.services.artist_service import ArtistService
+
+pytestmark = pytest.mark.integration
+
+
+@pytest.mark.asyncio
+async def test_find_or_create_creates_new(db):
+    svc = ArtistService(db)
+    artist, created = await svc.find_or_create("Brand New")
+    assert created is True
+    assert artist.id is not None
+    assert artist.slug == "brand-new"
+
+
+@pytest.mark.asyncio
+async def test_find_or_create_idempotent_on_same_name(db):
+    svc = ArtistService(db)
+    a1, c1 = await svc.find_or_create("Alice")
+    a2, c2 = await svc.find_or_create("Alice")
+    assert c1 is True
+    assert c2 is False
+    assert a1.id == a2.id
+
+
+@pytest.mark.asyncio
+async def test_find_or_create_rejects_empty_name(db):
+    svc = ArtistService(db)
+    with pytest.raises(ValueError):
+        await svc.find_or_create("   ")
+
+
+@pytest.mark.asyncio
+async def test_autocomplete_ranks_exact_prefix_substring(db):
+    db.add_all([
+        Artist(name="Alice", slug="alice"),
+        Artist(name="Alice Cooper", slug="alice-cooper"),
+        Artist(name="Malice", slug="malice"),
+        Artist(name="Bob", slug="bob"),
+    ])
+    await db.flush()
+    svc = ArtistService(db)
+    rows = await svc.autocomplete("alice")
+    names = [r.name for r in rows]
+    assert names[0] == "Alice"                       # exact first
+    assert names[1] == "Alice Cooper"                # then prefix
+    assert "Malice" in names                         # then substring
+    assert "Bob" not in names
+
+
+@pytest.mark.asyncio
+async def test_autocomplete_empty_query_returns_empty(db):
+    svc = ArtistService(db)
+    assert await svc.autocomplete("") == []