viewer/nodes: fix WebGPU pipeline poisoning from missing uv2 on slabs and empty roofs

[connorsoohoo]

What does this PR do?

Fixes the WebGPU error cascade (Color target has no corresponding fragment stage output → Invalid RenderPipeline → Invalid CommandBuffer on every queue submit) that fires when a scene contains slabs or segment-less roofs whose default catalog finish carries an aoMap — most visibly when loading IFC files in apps/ifc-converter.

Root cause: two geometry producers ship meshes without a uv2 attribute while their slot material samples uv2 (aoMap):

• buildSlabGeometry's top/side face split rebuilt geometries with only position + uv; the default surface finish library:wood-woodplank48 has an AO map.
• The children-less merged-roof fallback assigned BoxGeometry(0, 0, 0), which has uv but no uv2; roofs imported from IFC have no segments, so they all hit this branch.

three r184's WebGPU renderer throws mid scene pass on the referenced-but-missing attribute (Cannot read properties of undefined (reading 'id') in RenderObject.getAttributes), which leaves the post-processing MRT render target bound on the renderer — every pipeline compiled afterwards validates against the wrong 3-attachment framebuffer, and post FX permanently falls back once the retry budget is exhausted.

Changes:

• packages/nodes/src/slab/geometry.ts — emit uv2 (copy of uv) on the split top/side geometries, matching the existing ensureUv2Attribute convention.
• packages/viewer/src/systems/roof/roof-system.tsx — replace the BoxGeometry(0,0,0) fallback with ensureRenderableGeometryAttributes(new BufferGeometry()), which carries all four attributes and keeps a valid position for Drei's BVH.
• packages/viewer/src/components/viewer/post-processing.tsx — defense-in-depth: reset the render target when a render pass throws, so any future mid-pass exception costs one frame instead of poisoning every pipeline for the session.

How to test

1. bun install && bun dev, then open the IFC converter app (port 3003) and load the "Revit Architectural" example (?file=07-revit-architectural.ifc) — any example with slabs reproduces.
2. Before this PR: the console fills with THREE.AttributeNode: Vertex attribute "uv2" not found, [viewer/post-processing] Render pass failed., and repeating WebGPU uncaptured error: Invalid RenderPipeline / Invalid CommandBuffer entries; post FX (SSGI/ink) drops out after 3 retries.
3. After this PR: console is clean and the model renders with post-processing active.
4. Editor regression check: place a slab and a roof in the editor app, paint the slab top, delete all segments from a roof — no console errors, slab finish still tiles correctly (uv2 mirrors uv).

Screenshots / screen recording

N/A — the change is "errors gone": before, the converter console streams GPUValidationError spam and the viewer loses SSGI/ink; after, the same model loads with a clean console and full post FX.

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

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Note

Medium Risk
Touches WebGPU rendering and geometry attributes on common paths (IFC slabs/roofs); changes are narrow and align with existing ensureRenderableGeometryAttributes patterns, with low regression risk outside WebGPU/post-FX.

Overview
Fixes a WebGPU error cascade when slab or segment-less roof meshes use default finishes whose aoMap samples uv2, but the geometry only had position + uv.

Slab split geometry now mirrors uv into uv2 on top/side buffers (same convention as ensureRenderableGeometryAttributes). Empty merged roofs no longer use BoxGeometry(0,0,0); they use ensureRenderableGeometryAttributes(new BufferGeometry()) so BVH-safe position and uv2 are present.

Post-processing resets the render target to null when a render pass throws, so a mid-pass failure does not leave the MRT bound and poison subsequent pipeline compiles.

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