feat(fc3a): migration 0010 — unique(source.artist_id, platform, url)

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

tests/test_migration_0010.py

@@ -0,0 +1,35 @@
+import pytest
+from sqlalchemy.exc import IntegrityError
+
+from backend.app.models import Artist, Source
+
+pytestmark = pytest.mark.integration
+
+
+@pytest.mark.asyncio
+async def test_duplicate_artist_platform_url_rejected(db):
+    artist = Artist(name="Alice", slug="alice")
+    db.add(artist)
+    await db.flush()
+    db.add(Source(
+        artist_id=artist.id, platform="patreon",
+        url="https://patreon.com/alice", enabled=True,
+    ))
+    await db.flush()
+    db.add(Source(
+        artist_id=artist.id, platform="patreon",
+        url="https://patreon.com/alice", enabled=True,
+    ))
+    with pytest.raises(IntegrityError):
+        await db.flush()
+
+
+@pytest.mark.asyncio
+async def test_same_url_under_different_artist_ok(db):
+    a = Artist(name="A", slug="a")
+    b = Artist(name="B", slug="b")
+    db.add_all([a, b])
+    await db.flush()
+    db.add(Source(artist_id=a.id, platform="patreon", url="https://x/y", enabled=True))
+    db.add(Source(artist_id=b.id, platform="patreon", url="https://x/y", enabled=True))
+    await db.flush()  # must NOT raise