[codex] Reuse cached 3D model loads

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Summary

• Reuse completed STEP conversions before hydrating the saved GLB cache, so repeated STEP mounts do not create duplicate blob URLs.
• Add a shared load3DModel cache so repeated STL/OBJ/WRL/GLTF/GLB URLs reuse one in-flight/completed load instead of fetching and parsing duplicates.
• Return independent clones from cached model loads and evict failed loads so retries are not poisoned by a transient failure.
• Add regression coverage for registry-first STEP reuse, one-time saved-cache hydration, shared model-load dedupe, clone isolation, and failed-load retry.

Verification

• npm run format:check
• npx biome check src/utils/load-model.ts tests/load-model-cache.test.ts
• npx --yes bun test tests/load-model-cache.test.ts tests/step-model-cache.test.ts
• npx tsc --noEmit
• npm run build
• npm run test:node-bundle

Closes #93

/claim #93

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Project	Deployment	Actions	Updated (UTC)
3d-viewer	Ready	Preview, Comment	May 23, 2026 9:31am

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Quick review note for maintainers: this PR is intentionally scoped to the STEP cache lifecycle gap I mentioned in the attempt comment.

It checks the in-memory conversion registry before hydrating from the saved GLB cache, so remounting the same STEP model can reuse the existing converted file instead of creating another blob URL. I kept the fetch/conversion path unchanged and added focused regression coverage for registry-first reuse plus one-time saved-cache hydration.

Current GitHub checks are green, and the PR body lists the local verification commands I ran.

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Update: I pushed a second commit that broadens this PR from STEP cache reuse to the shared load3DModel path as well.

The new cache reuses one in-flight/completed load per URL, returns independent clones so callers can set transforms without mutating the cached source object, and evicts failed loads so a transient failure can be retried.

Verification run locally:

• npm run format:check
• npx biome check src/utils/load-model.ts tests/load-model-cache.test.ts
• npx --yes bun test tests/load-model-cache.test.ts tests/step-model-cache.test.ts
• npx tsc --noEmit
• npm run build
• npm run test:node-bundle

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One maintainer-facing verification note for the bounty claim: this PR is non-visual loader/cache work rather than a UI rendering change, so I verified it with focused regression tests plus the package checks/build instead of a demo video. The current checks are green, and the patch covers the duplicate in-flight/completed model load path while preserving independent clones and retry behavior after failed loads. Happy to add a short capture or narrow the scope further if that would make review easier.