feat(provenance): per-image artist on gallery scroll payload

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

tests/test_gallery_artist_payload.py

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+from datetime import UTC, datetime, timedelta
+
+import pytest
+
+from backend.app import create_app
+from backend.app.models import (
+    Artist,
+    ImageProvenance,
+    ImageRecord,
+    Post,
+    Source,
+)
+
+pytestmark = pytest.mark.integration
+
+
+@pytest.fixture
+async def app():
+    return create_app()
+
+
+@pytest.fixture
+async def client(app):
+    async with app.test_client() as c:
+        yield c
+
+
+async def _img(db, n):
+    rec = ImageRecord(
+        path=f"/images/ap/{n}.jpg", sha256=f"ap{n:062d}",
+        size_bytes=1, mime="image/jpeg", width=1, height=1,
+        origin="imported_filesystem", integrity_status="unknown",
+    )
+    rec.created_at = datetime.now(UTC) - timedelta(minutes=n)
+    db.add(rec)
+    await db.flush()
+    return rec
+
+
+async def _artist_source(db, name, slug):
+    a = Artist(name=name, slug=slug)
+    db.add(a)
+    await db.flush()
+    s = Source(artist_id=a.id, platform="patreon",
+               url=f"https://patreon.test/{slug}")
+    db.add(s)
+    await db.flush()
+    return a, s
+
+
+@pytest.mark.asyncio
+async def test_scroll_artist_via_primary_post(client, db):
+    rec = await _img(db, 1)
+    _, s = await _artist_source(db, "Alice", "alice")
+    post = Post(source_id=s.id, external_post_id="1")
+    db.add(post)
+    await db.flush()
+    rec.primary_post_id = post.id
+    await db.flush()
+    await db.commit()
+
+    resp = await client.get("/api/gallery/scroll?limit=10")
+    assert resp.status_code == 200
+    body = await resp.get_json()
+    item = next(i for i in body["images"] if i["id"] == rec.id)
+    assert item["artist"] == {"name": "Alice", "slug": "alice"}
+
+
+@pytest.mark.asyncio
+async def test_scroll_artist_via_provenance_fallback(client, db):
+    rec = await _img(db, 1)
+    _, s = await _artist_source(db, "Bob", "bob")
+    post = Post(source_id=s.id, external_post_id="2")
+    db.add(post)
+    await db.flush()
+    db.add(ImageProvenance(image_record_id=rec.id, post_id=post.id,
+                           source_id=s.id))
+    await db.flush()
+    await db.commit()  # rec.primary_post_id stays NULL
+
+    resp = await client.get("/api/gallery/scroll?limit=10")
+    body = await resp.get_json()
+    item = next(i for i in body["images"] if i["id"] == rec.id)
+    assert item["artist"] == {"name": "Bob", "slug": "bob"}
+
+
+@pytest.mark.asyncio
+async def test_scroll_artist_null_when_none(client, db):
+    rec = await _img(db, 1)
+    await db.commit()
+    resp = await client.get("/api/gallery/scroll?limit=10")
+    body = await resp.get_json()
+    item = next(i for i in body["images"] if i["id"] == rec.id)
+    assert item["artist"] is None