Four independent decomp studies (Opus 4.8 x2, Sonnet 4.6, external Codex)
converge: retail carries the cell through the collision sweep (validate_transition
advances curr_cell only on an accepted move, reverts on a block) and commits it in
SetPositionInternal — it never re-derives membership from a static resting position.
acdream already ports the sweep machinery (sp.CurCellId/CheckCellId, ValidateTransition,
CheckOtherCells) but ResolveWithTransition discards the swept cell and re-derives
statically via ResolveCellId (PhysicsEngine.cs:909/928) — the root of the
0170<->0031 doorway/cellar ping-pong. The do_not_load_cells prune is secondary
(static/cross-cell lists), not the anti-flicker; W2b was doubly misplaced and is reverted.
Render: one PView::ConstructView portal traversal over the same cell graph, rooted at
the physics current cell; seen_outside (not a dungeon flag) gates landscape; the outside
draws through exit portals clipped to the doorway (no blue-hole, no stencil split).
Dungeons/interiors share the machinery; "underground" is emergent.
Design doc lays out the staged, evidence-first rewrite (Stage 0 diagnostic ->
Stage 1 transition-owned membership [visual gate] -> Stage 2 CELLARRAY/prune parity ->
Stages 3-5 render root + PView seal + entity clip). Adds the shared research prompt and
all four study reports as the grounding record.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
