editor: add lean-to roof extensions and automatic drainage

[sudhir9297]

What does this PR do?

• Adds configurable wall-hosted lean-to roof extensions with registry-driven 2D/3D placement, movement, snapping, collision validation, selection proxying, parametric controls, framing, supports, flashing, paint slots, and managed roof children.
• Supports straight and short curved host walls on either side, including inner and outer L/V corner joins. Adjacent extensions coordinate their roof footprints, straight terminal cuts, side infill, rafters, posts, and mitres without duplicate or protruding assembly pieces.
• Adds automatic roof gutters, outlets, and terrain-aware downspouts. Straight and curved gutter runs are clipped and joined around lean-to corners, generated outlets cut the gutter floor, and manual drainage adjustments remain stable across later roof edits.
• Keeps derived extension and drainage assemblies synchronized through the shared Scene API, preserves old scenes through schema defaults/migrations, and follows the editor interaction, overlay, snapping, and 2D/3D parity contracts.

How to test

1. Run bun dev, open the editor, create a building, and place lean-to extensions from the Build panel on both faces of a straight wall; verify previews snap correctly and the extension is selected after placement.
2. Create internal and external L- and V-shaped wall corners, then place an extension on each adjoining wall. Verify the roof surfaces, flashing, rafters, posts, and gutters meet cleanly with no duplicate pillars, gray infill wedges, circular terminal caps, gaps, or protruding pieces.
3. Create a 2–3 m curved wall in both inward and outward configurations, connect it to a non-collinear straight wall, and place extensions on both. Verify the curved roof follows a concentric band, ends with a straight joint edge, and mitres into the neighboring straight extension without a triangular hole.
4. Move and resize extensions in both 3D and floorplan views. Switch snapping modes and dependency locks, and verify the high/low edges, pitch, overhangs, framing, supports, corner joins, and drainage remain synchronized.
5. Enable automatic gutters and downspouts on straight, segmented, and curved roofs. Verify gutters form connected corner joints, each generated outlet opens the gutter floor, and downspouts reach the resolved slab or terrain ground. Move a generated outlet/downspout manually and verify the adjustment survives another roof edit.
6. Run bun run lint, bun run check, bun run check-types, bun run test, and bun run build.

Screenshots / screen recording

Recording to be added — this is a visual and interactive change.

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

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Note

High Risk
Large cross-cutting change to scene mutations, roof drainage generation, and new lean-to assembly sync; bugs could corrupt child trees, duplicate/delete gutters incorrectly, or desync 2D/3D edits.

Overview
Introduces a lean-to-extension node (wall child, clone remap for host roof refs, canvas selection proxy to the extension) and surfaces it under Build → Roof Features & extensions via presentation.paletteGroup: 'roof-features'.

Automatic drainage on roof segments: autoGutter metadata drives generated gutter runs (roof-type sides, trim/sibling clipping, lean-to edge exclusions), planAutomaticDownspouts placement, and default downspouts with lengthMode: 'to-ground' and terrain-aware length resolution. Store create/update/delete paths refresh gutters and downspouts while preserving manual gutters and nearest-run ID stability.

Gutter/downspout modeling gains concentric arc runs (geometry bend, outlet lookup, corner mitres), lean-to-prescribed eave height/mitres metadata, grid/magnetic length handles, and a downspout system that keeps automatic lengths in sync via SceneApi.subscribeNodes / applyChanges.

SceneApi expands with createMany, applyChanges, and subscribeNodes; floorplan affordances/move targets and registry move tools receive sceneApi. Parametric derive can take previous; lean-to managed columns hide layout edits and trim handles.

Roof segments add optional arc and shed infill fields; accessory kinds get dedicated palette icons. Editor polish: resize snap non-finite fallback, contextual helpers during arrow resize, disabled segmented controls.

^{Reviewed by Cursor Bugbot for commit 0c7eb6a. Bugbot is set up for automated code reviews on this repo. Configure here.}

[cursor]

Multi-edit skips derive previous

Medium Severity

derive now takes a previous node so resize locks can compare pre-edit values, and the single-node inspector passes it, but buildMultiNodePatches still calls derive(next, patch) only. Lean-to derive defaults previous to next, so multi-select projection/pitch/height edits apply locks against already-patched values and can preserve the wrong edge.

Additional Locations (1)

• packages/nodes/src/lean-to-extension/parametrics.ts#L61-L79

 

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[cursor]

Downspouts ignore slab ground

High Severity

Automatic downspout length samples only persisted terrain (or 0) and never the slab under the drop. Posts already resolve slab support and level-base elevation, so pipes keep falling through decks and patios, and later slab moves are not treated as length dependencies.

Additional Locations (1)

• packages/nodes/src/downspout/system.tsx#L14-L22

 

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[cursor]

Cursor Bugbot has reviewed your changes using high effort and found 1 potential issue.

There are 3 total unresolved issues (including 2 from previous reviews).

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[cursor]

Prescribed gutter mitres exit too early

High Severity

computeGutterMitres now seeds both ends from prescribed lean-to mitres and still breaks once both values are nonzero. Adjacent lean-to runs therefore stop scanning after the first sibling, overwrite a prescribed corner with a geometric hit inside the 10 cm epsilon, or skip the true mate. Joined eaves can get the wrong cut or keep a cap.

 

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