Implement Phase 19 updates and user/editor verification

- Updated architectural specifications for Phase 19 scenery, backgrounds, and surface finishes to reflect implementation status and user verification results.
- Revised UI/UX specifications for background ground and wall color, plain background, and starter scene composition to indicate successful implementation and verification.
- Enhanced scenery controller and sandbox stage scripts to improve eraser functionality and user interactions.
- Adjusted test cases to align with the latest changes in scenery and background implementations, ensuring all checks pass successfully.
- Added new buttons for wall area erasure in the scenery capture bar and updated layout handling for better user experience.

docs/plans/phase_19_starter_scene_composition.md

@@ -1,6 +1,6 @@
 # Phase 19 — Starter Scene Composition
 
-> **Status:** Accepted product design for a focused Phase 19 starter-scene polish. This is a design handoff to the spec-pipeline, not a final technical specification.
+> **Status (2026-10-22):** Implemented and user/editor verified as part of Phase 19. The user verified both starter compositions in the editor; the Phase 19 scenery suite passes **706 checks with 0 failures**. The detailed composition decisions below remain the historical product and implementation brief.
 
 ## Goal and audience
 
@@ -46,18 +46,18 @@ The pre-implementation design review found the outdoor artwork bases roughly **1
 
 ## Current project behavior and references
 
-The Phase 19 [scenery product plan](phase_19_scenery_backgrounds_surface_finishes.md) defines the starter choices, editable scenery layers, and the distinction between visual Scenery and walkable Ground. The [Background Ground and Wall Color brief](phase_19_background_ground_and_wall_color.md) defines decorative Background ground and editable wall finishes. The [Phase 19 handoff](phase_19_handoff.md) says overall user/editor verification is still pending.
+The Phase 19 [scenery product plan](phase_19_scenery_backgrounds_surface_finishes.md) defines the starter choices, editable scenery layers, and the distinction between visual Scenery and walkable Ground. The [Background Ground and Wall Color brief](phase_19_background_ground_and_wall_color.md) defines decorative Background ground and editable wall finishes. The user/editor verification recorded in the [Phase 19 handoff](phase_19_handoff.md) is complete. The later [Plain Background brief](phase_19_plain_background.md) adds Plain Background and renames the former neutral-Sky Blank Scene choice **Open Sky**.
 
 The accepted visual direction is detailed in the [starter-scene UI/UX specification](../specs/phase_19_starter_scene_composition_ui_ux.md). The implementation contract is in the [approved starter-scene architecture specification](../specs/phase_19_starter_scene_composition.md).
 
 Before this composition pass, the [Town Street scene](../../content/stages/starters/town_street.scene) used one Far skyline, separate Near trees/buildings, and short Sidewalk/Asphalt Ground runs. The [Living Room scene](../../content/stages/starters/living_room.scene) used three wall panels, seven Wood Ground pieces, separate decorations, and three Props. Both saved zoom 0.5. The implementation now promotes these starters to current scene format v1.6, extends required surfaces to the approved envelope, and frames starter previews from the saved camera. See the focused [architecture specification](../specs/phase_19_starter_scene_composition.md) for exact placements and verification results. The existing artwork and furniture remain in [content/props](../../content/props/), with each placement independently editable.
 
-## Verification status and remaining checks
+## Verification status
 
-- The focused composition suite passes 515 assertions, including tile bounds, seam navigation, a physical PLAY step from sidewalk to road, and Living Room floor support.
-- A render-capable capture route is not available in this run: the bounded GUI capture exited 134 without producing an image. Visual checks remain for the opening frames, pan endpoints, tile/background joins, starter cards, narrower viewport, and zoom-in framing.
-- The broader scenery suite still exits 1 on nine Sky-preview/gallery and Scenery-edit interaction assertions; Town/Living Room surface assertions pass and those nine failures were also present before the latest tile and curb changes.
+- The focused composition suite passed 515 assertions, including tile bounds, seam navigation, a physical PLAY step from sidewalk to road, and Living Room floor support.
+- The earlier broad-suite run recorded nine failures; that result was superseded by the 2026-10-22 retest, which passed the Phase 19 scenery suite with 706 checks and 0 failures.
+- The user completed editor visual verification of Town Street and Living Room, including the composition behaviors and surfaces covered here.
 
 ## Implementation status
 
-The initial focused composition test passed 177 assertions, but user visual review found clouds visible through the Town Street below the skyline and rejected the oversized scaled walkable blocks. The revision adds opaque Grass Background ground, ordinary-size tile rows, and a one-tile Asphalt extension at each end so characters can reach the road. The focused composition suite now passes 515 assertions, including routing across tile seams and a grounded PLAY drop onto Asphalt. Rendered review and user/editor checks remain pending. The [architecture specification](../specs/phase_19_starter_scene_composition.md) records the measurements and test limitations.
+The initial focused composition test passed 177 assertions, but user visual review found clouds visible through the Town Street below the skyline and rejected the oversized scaled walkable blocks. The revision adds opaque Grass Background ground, ordinary-size tile rows, and an Asphalt extension so characters can reach the road. The focused composition suite passed 515 assertions, including routing across tile seams and a grounded PLAY drop onto Asphalt. The user has since completed the editor visual review; current Phase 19 test and verification results are summarized above and in the [handoff](phase_19_handoff.md).