feat(artist): editable display name + rename surface; drop name-uniqueness (#130 step 1)

First step of decoupling artist identity/storage/display. migration 0077 drops
uq_artist_name so the display name is free text (two genuinely different creators
can share a name); the slug stays the immutable, unique storage/identity key (the
on-disk path component — untouched, so nothing moves). ArtistService.rename +
PATCH /api/artists/<id> change the name ONLY. Frontend: inline pencil-edit on the
artist header (mirrors TagCard), slug/route unaffected so no navigation. Fixes the
operator's 'no surface to rename an artist' + the name-collision fragility.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01CDgx8bQS5YrGRK76v8HUnM

backend/app/api/artists.py

@@ -31,6 +31,24 @@ async def create_or_get():
     }), 201
 
 
+@artists_bp.route("/<int:artist_id>", methods=["PATCH"])
+async def rename(artist_id: int):
+    """Rename an artist's DISPLAY NAME (#130). Name only — the slug and every
+    on-disk path stay put, so this is instant and safe. Name is non-unique."""
+    body = await request.get_json()
+    if not isinstance(body, dict) or not isinstance(body.get("name"), str):
+        return jsonify({"error": "invalid_body"}), 400
+    async with get_session() as session:
+        svc = ArtistService(session)
+        try:
+            artist = await svc.rename(artist_id, body["name"])
+        except ValueError as exc:
+            return jsonify({"error": "empty_name", "detail": str(exc)}), 400
+        if artist is None:
+            return jsonify({"error": "not_found"}), 404
+        return jsonify({"id": artist.id, "name": artist.name, "slug": artist.slug})
+
+
 @artists_bp.route("/autocomplete", methods=["GET"])
 async def autocomplete():
     q = request.args.get("q") or ""

backend/app/models/artist.py

@@ -15,7 +15,14 @@ class Artist(Base):
     __tablename__ = "artist"
 
     id: Mapped[int] = mapped_column(Integer, primary_key=True)
-    name: Mapped[str] = mapped_column(String(255), nullable=False, unique=True)
+    # Display name: freely editable, NON-unique (two real creators can share a
+    # name). Decoupled from identity/storage in migration 0077 (#130) — renaming
+    # touches ONLY this. Was unique until then.
+    name: Mapped[str] = mapped_column(String(255), nullable=False)
+    # Storage/identity key: IMMUTABLE + unique. This is the on-disk path
+    # component (download_service artist_slug = artist.slug → images_root/<slug>/
+    # <platform>/…), so it is set once at creation (collision-suffixed) and NEVER
+    # changes — a rename must not move files. Existing artists keep their slug.
     slug: Mapped[str] = mapped_column(String(255), nullable=False, unique=True)
     notes: Mapped[str | None] = mapped_column(Text, nullable=True)
 

backend/app/services/artist_service.py

@@ -283,6 +283,23 @@ class ArtistService:
             await self.session.commit()
         return artist, created
 
+    async def rename(self, artist_id: int, name: str) -> Artist | None:
+        """Change the display NAME only (#130). The slug — and every on-disk path
+        keyed off it — is IMMUTABLE, so a rename never moves files or risks a path
+        collision. Name is free text and NON-unique (migration 0077). Returns the
+        updated Artist, None if not found; raises ValueError on empty name."""
+        cleaned = (name or "").strip()
+        if not cleaned:
+            raise ValueError("artist name must not be empty")
+        artist = (await self.session.execute(
+            select(Artist).where(Artist.id == artist_id)
+        )).scalar_one_or_none()
+        if artist is None:
+            return None
+        artist.name = cleaned
+        await self.session.commit()
+        return artist
+
     async def autocomplete(self, prefix: str, limit: int = 20) -> list[Artist]:
         cleaned = (prefix or "").strip()
         if not cleaned: