~anthropic/claude-sonnet-latest → A (6:4)

Commit A fixes actual product logic (sibling nav grouping so each unranked sibling is its own group) with a targeted test verifying the behavior, directly affecting user-facing rendering correctness. Commit B is a dev-tooling improvement to the fixture script (persistent data dir, cargo-watch) plus an unrelated removal of room header markup in forum.rs that looks like accidental regression/noise, making it less clearly a net positive for lasting product value.