feat(provenance): _artists_for resolves via artist_id (closes vii-b gap)

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

backend/app/services/gallery_service.py

@@ -13,7 +13,7 @@ from datetime import datetime
 from sqlalchemy import and_, exists, func, or_, select
 from sqlalchemy.ext.asyncio import AsyncSession
 
-from ..models import Artist, ImageProvenance, ImageRecord, Post, Source, Tag
+from ..models import Artist, ImageProvenance, ImageRecord, Source, Tag
 from ..models.tag import image_tag
 
 CURSOR_SEPARATOR = "|"
@@ -94,44 +94,19 @@ def _provenance_clause(post_id, artist_id):
 
 
 async def _artists_for(session, image_ids: list[int]) -> dict[int, dict]:
-    """Map image_id -> {"name","slug"} using the primary-post path first,
-    then the lowest-id ImageProvenance row as fallback. Bounded by page
-    size (<= 200) → two indexed selects, no N+1."""
+    """Map image_id -> {"name","slug"} via the canonical
+    image_record.artist_id (FC-2d-vii-c). Bounded by page size."""
     if not image_ids:
         return {}
-    out: dict[int, dict] = {}
-
-    primary = (
+    stmt = (
         select(ImageRecord.id, Artist.name, Artist.slug)
-        .join(Post, Post.id == ImageRecord.primary_post_id)
-        .join(Source, Source.id == Post.source_id)
-        .join(Artist, Artist.id == Source.artist_id)
+        .join(Artist, Artist.id == ImageRecord.artist_id)
         .where(ImageRecord.id.in_(image_ids))
     )
-    for img_id, name, slug in (await session.execute(primary)).all():
-        out[img_id] = {"name": name, "slug": slug}
-
-    remaining = [i for i in image_ids if i not in out]
-    if remaining:
-        fb = (
-            select(
-                ImageProvenance.image_record_id,
-                ImageProvenance.id,
-                Artist.name,
-                Artist.slug,
-            )
-            .join(Source, Source.id == ImageProvenance.source_id)
-            .join(Artist, Artist.id == Source.artist_id)
-            .where(ImageProvenance.image_record_id.in_(remaining))
-            .order_by(
-                ImageProvenance.image_record_id.asc(),
-                ImageProvenance.id.asc(),
-            )
-        )
-        for img_id, _pid, name, slug in (await session.execute(fb)).all():
-            if img_id not in out:  # first (lowest id) wins
-                out[img_id] = {"name": name, "slug": slug}
-    return out
+    return {
+        img_id: {"name": name, "slug": slug}
+        for img_id, name, slug in (await session.execute(stmt)).all()
+    }
 
 
 class GalleryService: