Wall lifecycle: rectangle walls, loop-cut split and merge, with 2D navigation and selection fixes

[AxiomeCG]

What does this PR do?

Completes the wall lifecycle — draw, split, merge — and fixes four main bugs found while testing it in the floor plan. Balconies and the plan workspace (calibrate / trace SVG plans) follow in separate PRs stacked on this one.

Walls

• Rectangle walls: R toggles line / rectangle inside the wall tool (HUD "Shape" chip cycles the same store). In 2D the rectangle drafts through the plan's own cursor, snapping, mitered footprints and measurement plates; in 3D it keeps the wall cursor and the line draft's look.
• Split as a loop cut, driven by the HUD: scrolling sets 1–32 cuts, one cut follows the pointer with the snapping modes (Shift cycles, Ctrl tap steps the grid, Alt frees), several divide the wall evenly, and a click commits them as one undo step (planWallDivisions). Openings re-host on their segment. The old floating panel is gone.
• Merge adjoining walls: select walls that continue each other → "Merge" next to Split (same component in 2D and 3D). planWallMerge keeps the wall with the most attachments and never turns it around; an absorbed wall read backwards mirrors its children's local frame (side, depth, yaw — hinges and swing hang off the yaw and stay as stored); every child is re-hosted at its world position, stale child ids are dropped, rooms follow; it refuses T/cross joints, walls out of line, different thickness / visible height / finish, or curved walls — the reason shows on hover.
• Rectangle sides reuse existing walls: a side drawn along an existing wall inserts only the uncovered remainder (uncoveredWallSegments); a side that T-joins or crosses a room wall keeps the room on the replacement walls.
• Openings keep their metadata when moved; transient previews never host walls; windows place through grid events on hidden walls.

Behaviour changes on main that come with the shared planners (worth knowing when reviewing):

• planWallInsertion — the line tool's planner too — now rewrites a room's boundaryWallIds when it splits one of that room's walls; before, the zone kept the removed wall's id.
• The delete heal's joining rule and attachment re-hosting (resolveMergedWallEndpoints, buildMergedWallAttachmentUpdates) moved from node-actions.ts into systems/wall/wall-merge.ts; at a start-to-start joint the heal no longer reverses the kept wall (which flipped its frontSide / backSide and hosted faces).

Where it lives. Split and merge are wall code, so they live in packages/nodes/src/wall/ (split-session.ts, split-store.ts, split-preview.ts, split-pointer.ts, split-tool.tsx, split-floorplan-layer.tsx, actions.tsx). The editor only gains kind-agnostic seams, so the next kind-owned reshape needs no editor change:

• ToolManager mounts def.affordanceTools[reshape] for any reshaping scope without a dedicated arm (the split runs as reshape: 'split', which also gives it the polygon snapping chip).
• FloorplanRegisteredToolLayer mounts the floorplan extension's reshapeLayers[reshape] while that scope runs.
• HelperManager renders def.affordanceHints[reshape] (the cut-count chip) like toolHints.
• NodeActionMenu renders the floorplan extension's actionMenu.actions for the selected kinds (Split / Merge come from the wall).
• Slab and ceiling declare selectionCounterparts on the same extension for the paired deselect below.

Known gap, left for a follow-up: the 3D rectangle draft has no alignment guides yet (the 2D one shares the line draft's).

Fixes on main (each its own commit)

• WASD and orbit did nothing in 2D-only view (the 3D canvas is paused there since perf: tighten viewer runtime ownership #675, and a session opened straight into 2D never mounted the camera). The plan owns them in 2D-only view with the camera's key state, guards and speed (lib/keyboard-pan.ts) and publishes the pose to 3D when the move ends.
• Drawing onto an existing wall in 2D selected it instead of placing the point: registry entries now yield to the active tool in build mode, as 3D does; T-junctions draw in 2D.
• Group selection box: it measured world-space meshes (wrong under a rotated building, unbuilt in 2D-only view) and grew the selection to every connected wall. Group transforms now act on the selection (connected walls stretch at their shared ends), and the box is measured from plan data (groupPlanBounds); the 2D box, 3D rotate gizmo and keyboard R/T share its centre. This is a behaviour change: two walls of a room no longer move the whole room.
• A room's slab and ceiling deselect together in the plan (the ceiling is drawn as an unfilled outline a click can't reach; a marquee still picks it).

How to test

1. bun dev, open a scene with a few rooms, switch to the 2D view.
2. Wall tool: press R — the HUD shows Shape: Rectangle; click two opposite corners → four joined walls, mitered, with plates during the draft. Press R again → line mode; end a wall on the side of an existing wall → a T-junction, not a selection.
3. Select a wall → scissors (Split): scroll to change the cut count, Shift to cycle snapping, click to commit; undo once removes all cuts. Select the two halves → Merge (two arrows) → one wall again; hover a greyed Merge to read why.
   • Draw two walls toward each other (start-to-start), put a door on one, merge: the kept wall keeps its facing and the door keeps its hinge in the world. Draw a rectangle whose side runs along an existing wall and past its end: the overhang is added, not a doubled wall. Draw a rectangle whose side T-joins a room's wall: the room stays one zone.
4. In 2D-only view, hold WASD and use the orbit buttons: the plan moves / turns; switch to 3D — the camera is where the plan left it.
5. Marquee a room (walls + slab + ceiling): the dashed box hugs the room; Shift-click the slab → the ceiling leaves with it and the box hugs the walls. Rotate the building first to check the box stays on the walls.
6. bun test in packages/{core,editor,nodes} (all green), bun check.

Screenshots / screen recording

Screen recording to be added by the author (2D rectangle draft, loop-cut split, merge).

Checklist

• I've tested this locally with bun dev
• My code follows the existing code style (run bun check to verify)
• I've updated relevant documentation (if applicable)
• This PR targets the main branch

🤖 Generated with Claude Code

https://claude.ai/code/session_017sG15rKXusC8rbBg6gjSRm

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Note

Medium Risk
Changes wall topology, opening re-hosting, and zone boundary references; group-move behavior no longer drags entire connected wall components, which can surprise users but is localized to editor geometry.

Overview
Adds core wall planners for rectangle drawing (planWallRectangle + uncoveredWallSegments to reuse collinear walls), explicit split/division (planWallDivision / planWallDivisions), and merge (planWallMerge in wall-merge.ts, shared with delete-heal). Merge/split paths re-host openings (including frame mirroring when a wall is read backwards), update zone boundaryWallIds, and validate collinearity, joints, and style.

Editor integration: registry seams for kind-owned reshapes (reshapeLayers, affordanceHints, actionMenu.actions), floorplan rectangle wall draft preview, and build-mode clicks that yield to tools instead of selecting walls underneath. Group transforms no longer auto-expand to every connected wall; the dashed box / gizmo pivot uses level-frame plan bounds (groupPlanBounds / computeGroupPlanBox). 2D-only view drives WASD/orbit via shared keyboard-pan while the 3D camera is paused; slab/ceiling deselect together in the plan via selectionCounterparts.

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