Clear stale STEP model while new URL loads

[YunHeTracyLee]

/claim #93

Summary

• Clear StepModel's derived stepGltfUrl at the start of each new stepUrl load, so a previously converted STEP model is removed while the next STEP conversion is pending.
• Add focused React coverage for switching from a cached STEP model to a new pending STEP URL.

Non-overlap

This is scoped to the STEP React lifecycle state for URL changes. It does not add or change STEP cache-key normalization, completed/blob reuse, temporary conversion resource disposal, generic load3DModel caching, GLTF lifecycle cleanup, OBJ/WRL loader behavior, or STL handling covered by existing PRs.

Validation

• npx --yes bun test tests/step-model-url-change.test.tsx with bunfig.toml temporarily moved aside to bypass the repo-wide sharp/looks-same preload; focused test passed.
• npx biome check src/three-components/StepModel.tsx tests/step-model-url-change.test.tsx
• npx tsc --noEmit --pretty false
• npm run build
• npm run test:node-bundle
• git diff --check

Local environment note

The default bun test preload imports looks-same/sharp; local dependencies were installed with scripts disabled, so the focused React test was run without the unrelated snapshot preload and bunfig.toml was restored afterward.

AI-assisted with Codex; I reviewed the diff and validation results before submitting.

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Project	Deployment	Actions	Updated (UTC)
3d-viewer	Ready	Preview, Comment	May 24, 2026 2:39pm