Bite-sized TDD plan for design Stages 0-1 + W2b revert + visual gate: add the
[cell-swept] diagnostic, return the swept sp.CurCellId from ResolveWithTransition
(retail SetPositionInternal), revert the superseded W2b hysteresis, visual-gate the
doorway/cellar strobe, then lock it with a doorway replay regression. Render chunk
(Stages 3-5) gets its own spec+plan after this gate.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>