feat(backfill): include artist_id in session migration

scripts/backfill/__tests__/migrateRoom.test.ts

@@ -77,6 +77,12 @@ describe("migrateRoom", () => {
     const stats = await migrateRoom(room, { dryRun: false });
 
     expect(insertSession).toHaveBeenCalledTimes(1);
+    expect(insertSession).toHaveBeenCalledWith(
+      expect.objectContaining({
+        account_id: "acc-1",
+        artist_id: null,
+      }),
+    );
     expect(insertChat).toHaveBeenCalledTimes(1);
     // one batch call containing only the well-formed message
     expect(upsertChatMessages).toHaveBeenCalledTimes(1);
@@ -102,6 +108,12 @@ describe("migrateRoom", () => {
     expect(insertChat).not.toHaveBeenCalled();
   });
 
+  it("passes room.artist_id into insertSession for straggler rooms", async () => {
+    await migrateRoom({ ...room, artist_id: "artist-1" }, { dryRun: false });
+
+    expect(insertSession).toHaveBeenCalledWith(expect.objectContaining({ artist_id: "artist-1" }));
+  });
+
   it("skips session/chat inserts when they already exist (idempotent re-run)", async () => {
     vi.mocked(selectSessions).mockResolvedValue([{ id: "s1" } as any]);
 

scripts/backfill/migrateRoom.ts

@@ -104,6 +104,7 @@ export async function migrateRoom(
     const session = await insertSession({
       id: sessionId,
       account_id: room.account_id,
+      artist_id: room.artist_id,
       title,
       created_at: room.updated_at,
       updated_at: room.updated_at,