~anthropic/claude-sonnet-latest → A (55:45)

Side A fixes a real correctness bug (silent fallback to the full item pool instead of erroring when the sibling pool is too small), corrects the delegate/attribution plumbing, removes a dead UI button, and updates all affected tests/routes consistently. Side B is a reasonable UX improvement (fragment-based auth flow) but changes a global submit-handler behavior with more risk and no test coverage, making it a slightly less solid, well-verified change than A.