# Slice H-a4 — retained frame scratch and diagnostic traversal

## Scope

This is a behavior-preserving ownership/allocation correction. It does not
change retail visibility, PView construction, spatial ordering, collision
debug drawing, title facts, or lifecycle checkpoint facts.

## Findings

Three independent steady-frame allocation sources remained:

1. `WorldSceneRenderer` constructed one `RetailPViewFrameInput` reference
   object for every PView frame even though `DrawInside` consumes it
   synchronously.
2. `GpuWorldState.LandblockEntries` and `LandblockBounds` were C# iterator
   methods, so merely obtaining each sequence constructed fresh iterator
   state. The underlying spatial membership changed only at update-thread
   publication boundaries.
3. `WorldSceneDiagnosticsController` passed
   `ShadowObjectRegistry.AllEntriesForDebug()` to the DebugVM publisher even
   when no developer UI consumer existed. The publisher correctly avoided
   enumeration, but the yield sequence itself had already been constructed.

The execution plan initially described landblock visibility counting as an
unconsumed diagnostic. That was incorrect in the current application:
`WorldRenderFrameOutcome` feeds the always-visible FPS/title `lb V/T` values
and connected lifecycle snapshots. Returning a neutral count would therefore
change observable behavior and invalidate lifecycle evidence. The count is
retained; only its iterator allocation is removed.

## Implementation

- `WorldSceneRenderer` owns one `RetailPViewFrameInput` and resets every field
  before the synchronous `DrawInside` call. The input is publicly read-only
  and internally mutable so downstream render owners cannot change borrowed
  frame facts.
- `GpuWorldState` exposes retained entry, no-animated-index entry, and bounds
  lists. They rebuild only after landblock membership, resident entity-list,
  animated-index, or AABB changes. Existing render-traversal slot order is
  preserved exactly.
- Landblock diagnostic counting uses indexed access over the retained bounds
  view.
- Shadow enumeration is constructed only when the DebugVM is mounted. The
  independent collision-wireframe switch keeps its existing enumeration.
- `InteriorEntityPartition` remains untouched while the G4 referee is still
  retained. Its removal and issue #241 close remain G5 work after the user
  accepts the G4 visual gate.

## Conformance

- Stable retained render-view getters allocate zero bytes over 1,000 polls.
- A spatial mutation refreshes the same borrowed list identity and publishes
  the new count.
- Two successive PView frames receive the same input object, reset with the
  current frame values.
- Existing quiescence, render traversal, animated-index, PView executor,
  abort/recovery, and DebugVM tests remain unchanged in behavior.

## Rollback boundary

This work is independent of the G4 production-source cutover. If tomorrow's
visual gate rejects G4, use:

```text
git revert ef1d263337997bb030eadb7b8e71d73dc659907a
```

Do not revert this Slice H-a4 commit, G3, or the portal-warmup corrections.