Add tests for scenery surface caching and preview behavior

- Introduced `test_scenery_brick_preview.gd` to validate focused placement and CPU draw-cost for large brick walls.
- Added `test_scenery_surface_cache.gd` to assess texture budget, visual equivalence, and cache invalidation.
- Created `test_scenery_surface_preview.gd` to evaluate adaptive preview selection and placement behavior.
- Implemented various helper functions to measure drawing performance and validate expected behaviors during tests.
- Added unique identifiers for new test files to ensure proper tracking and management.

docs/architecture/tech_debt_and_optimizations.md

@@ -178,4 +178,8 @@ This document tracks known technical debt, optimization opportunities, and minor
 | 2026-10-17 | Wrote the Phase 19 selected-artwork depth inspector specification (`docs/specs/phase_19_selected_artwork_depth_inspector.md`) for final sign-off. It reuses the existing `StageInspectorPanel` and `StagePanelChoiceGroup`, applies Far/Near/On the floor immediately to one live or missing Scenery placement through `StageSceneryArtwork.set_depth()`, and follows the Stage's existing dirty/save path. The current `.scene` depth field, `StageDrawOrder`, and `stage_panels` tokens need no changes. Updated #72 to include immediate depth edits in a future Stage-wide Undo phase. No runtime code changed by this specification entry. |
 | 2026-10-17 | Wrote the Phase 19 Background ground and wall color architecture specification (`docs/specs/phase_19_background_ground_and_wall_color.md`) for final sign-off. It defines distinct inert wall/backdrop scene types over a small shared rectangle contract, world-aligned bounded vector materials, selected-piece color preview without mutating saved tint, one eight-color Stage settings list, scene v1.6 migration of old Brick/Wood placeholder green, shared Stage inspector controls, and confirmed single-piece backdrop erasure. Logged #74 for zoom-consistent motif budgets and #75 for the old unused wall-color ambiguity. No runtime code changed. |
 
+| 2026-10-20 | Approved the scenery bitmap tile cache architecture (`docs/specs/scenery_bitmap_tile_cache.md`). Lightweight `StageSurfaceCache` handles share immutable bitmap tiles through one `StageSurfaceBakePool` under the current scene, with a 64 MiB resident bitmap budget and one reusable offscreen baker. Camera-visible tiles use four fixed zoom levels (0.125, 0.5, 1, 2); the coarsest tile bakes first and refined detail overlays it. At maximum 6× zoom, the 2× bitmap may look softer because it is magnified threefold. Erased fragments clip shared tiles only when their complete pattern sampling phase matches. The previous per-surface viewport cache retained vector commands and had no scene-wide resource limit, a likely contributor to `Element limit reached`; the exact RID pool remains unconfirmed. GPU readback during bitmap capture and regeneration after budget eviction are accepted costs to measure during implementation. |
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+| 2026-10-20 | Replaced the positional scenery tile design after the user observed continuous buffering when panning after zoom. The accepted revision in `docs/specs/scenery_bitmap_tile_cache.md` bakes one seamless, 2× bitmap per finish/tint period and uses GPU repeat plus generated mipmaps for all camera positions and zooms. Erased fragments share the style texture and crop it using their existing sample coordinate. The scene-wide 64 MiB limit includes mipmaps; inactive style variants may be evicted, while recently used styles stay warm when space allows. This trades unique random detail across an unlimited wall for finite repeated variation and keeps the existing possible 3× bitmap enlargement at maximum zoom. A style change can bake once; repeated camera movement must not increment build or readback counts after styles are ready. |
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 _End of Log_