Add Phase 19 Starter Scene Composition UI/UX Specification and Tests

- Introduced a new UI/UX specification document for the Phase 19 Starter Scene Composition, detailing user paths, composition rules for Town Street and Living Room, camera framing, and observable acceptance outcomes.
- Implemented a visual capture test for different sky states in the sandbox stage, ensuring proper rendering and visual consistency.
- Created a comprehensive test suite for the Phase 19 starter scene composition, validating scene loading, geometry, navigation, and interaction behaviors for both Town Street and Living Room.
- Added checks for visual alignment, object placements, and scene transitions to ensure adherence to the new UI/UX specifications.

docs/architecture/tech_debt_and_optimizations.md

@@ -85,6 +85,8 @@ This document tracks known technical debt, optimization opportunities, and minor
 | 73  | **Whole-set transform requires cross-system invariants** — Phase 19's temporary group transform covers only inert Scenery pieces: wall panels, artwork, and the planned Background ground. | Medium | Future feature | Moving/scaling walkable Ground, characters, interactive Props, Sky, camera composition, waypoints, and rules together needs separate physics, navigation, event-target, and save contracts. Do not expand the Scenery group tool into a whole-set transform without that design. See `docs/specs/phase_19_scenery_backgrounds_surface_finishes.md` and `docs/specs/phase_19_background_ground_and_wall_color.md`. (2026-10-17) |
 | 74  | **Background surface motifs need a shared zoom-consistent draw budget** — a pattern detail scale derived from each panel's size can shift seams or texture density where adjacent pieces meet, while uncapped large rectangles can issue excessive draw calls. | Medium | Planned | Phase 19 follow-up uses world-cell coordinates, visible-region culling, and any level-of-detail choice derived from camera zoom for all pieces in the same view. Keep Grass/Concrete/Carpet detail deterministic and bounded; consider a texture cache only if measured scenes remain expensive. See `docs/specs/phase_19_background_ground_and_wall_color.md`. (2026-10-17) |
 | 75  | **Old Brick/Wood wall colors were saved but not rendered** — v1.5 walls can carry the old default green while their brick and wood palettes were hard-coded. | Low | Planned migration | Scene v1.6 migration replaces only the old green placeholder on pre-v1.6 Brick/Wood entries with natural finish defaults; Paint and non-placeholder colors remain. The exact placeholder could have been intentionally authored in an older file, which cannot be distinguished retrospectively. New v1.6 colors are authoritative, including green Brick/Wood. See `docs/specs/phase_19_background_ground_and_wall_color.md`. (2026-10-17) |
+| 76  | **Camera-aware Sky redraws vector motifs while framing changes** — the former static Sky drew motifs only when the preset or viewport changed. | Low | Planned | The Phase 19 Sky addition keeps one screen-space `StageSkyView`, redraws only when a bound camera's effective framing changes, and caches reusable cloud/moon curve samples where practical. Measure sustained pan/zoom cost in a rendered Stage before adding a raster or shader path. The fixed reference frame and bounded response can saturate at distant camera positions; that is an accepted composition trade-off, not scene state to persist. See `docs/specs/phase_19_scenery_backgrounds_surface_finishes.md#phase-19-addition-camera-aware-sky-details`. (2026-10-21) |
+| 77  | **Starter surfaces guarantee a finite pan envelope, not arbitrary camera framing** — the two bundled sets use a fixed authored width to keep their scene data simple. | Low | Implemented; visual review pending | The authored envelope is a 1,280-logical-pixel viewport at zoom 0.5, ±1,000 world units of travel, and 100 units of margin per side. User review prompted an opaque Town Grass Background ground and separate scale-1 tile rows. Twenty-five 192-unit tiles cover the 4,760-unit minimum; Asphalt has 27 tiles (5,184 units) so the road extends one tile beyond the sidewalk at both ends. Navigation merges contiguous tile tops and routes the 32-unit curb step at the exposed ends without merging Ground objects or colliders. The focused suite passes 515 assertions, including the curb step and PLAY landing. The camera remains unrestricted, so wider viewports, farther pans, and zoomed-out shots can reveal finite ends. Rendered seam review remains pending. See docs/specs/phase_19_starter_scene_composition.md. (2026-10-21)
 
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@@ -181,5 +183,9 @@ This document tracks known technical debt, optimization opportunities, and minor
 | 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. |
 
 | 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. |
+| 2026-10-21 | Drafted the camera-aware Sky architecture addendum in `docs/specs/phase_19_scenery_backgrounds_surface_finishes.md` for user sign-off. Accepted a fixed built-in camera reference, one bounded response profile per preset, and normalized motif anchors with uniform scaling. The gradient remains a full-screen `CanvasLayer` draw; motifs derive deterministic bounded pan/zoom response from absolute `Camera2D` framing. Chooser and starter previews stay unbound and still; existing Sky/camera scene fields suffice. The trade-offs are response saturation far from the reference and more frequent vector redraws during camera movement; logged #76 for measured performance follow-up. No runtime code or tests changed. |
+| 2026-10-21 | Wrote the Phase 19 starter-scene composition UI/UX and architecture specifications (`docs/specs/phase_19_starter_scene_composition_ui_ux.md`, `docs/specs/phase_19_starter_scene_composition.md`) after approval of the Everyday Storybook brief and the 1,280-pixel / ±1,000-world-unit pan defaults. The edited starter snapshots use current scene v1.6 and existing Ground, wall, Background ground, Scenery, and Prop types, and keep the camera unrestricted; the starter card derives a central opening preview without new scene metadata. No code or art changed. Added #77 for the finite authored-envelope and broad-selection trade-off; the architecture spec is approved and implementation/agent verification are underway.
+| 2026-10-21 | Implemented the approved starter-scene composition spec. Town Street and Living Room now use continuous 4,760-unit support surfaces, aligned bases, and camera-derived starter-card framing; both edited scene files use current v1.6. The focused production-load/save-reopen/PLAY composition test passed 177 assertions, with measured visible-contact geometry within 0.225 logical pixels. The broader scenery suite exits 1 on nine other background-card and wall-erasure/capture-bar assertions, while the new surface assertions pass. GUI capture exited 134 and headless capture produced no image, so rendered-pixel checks, pan-endpoint seam inspection, narrow viewport/zoom-in framing, and user/editor verification remain pending. Updated #77 from planned to implemented with the finite-camera limitation accepted. See `docs/specs/phase_19_starter_scene_composition.md`.
+| 2026-10-21 | Revised the starters after the user's Town Street screenshot exposed Sky clouds below the skyline and the user rejected oversized scaled Ground blocks. Added an opaque Grass Background ground, replaced the sidewalk and both starter floors with scale-1 tile rows, and extended Asphalt by one tile at each end so the road is accessible. The focused production-path test passed 515 assertions, including navigation across tile seams, sidewalk-to-road routing, and a PLAY actor landing grounded on Asphalt. The broader scenery suite still exits 1 on the same nine Sky-preview/gallery and Scenery-edit UI assertions observed before this revision; its new surface assertions pass. A bounded GUI capture exited 134 without an image, so rendered pixels, pan endpoints, card previews, narrow viewport/zoom-in states, and user/editor review remain pending. See `docs/specs/phase_19_starter_scene_composition.md`.
 
 _End of Log_