DRAFT: opt-in live PNG texture preview with bounded watcher (#252)

[JayceeB1]

Purpose

Experimental, opt-in second slice of upstream lightningpixel/modly#252, originally contributed by @OmarB97. Builds on our explicit Artist Context PR #6. Neither fork main nor upstream is changed.

User-visible behavior

The 3D viewer gets a Watch texture control. The OS file dialog selects a PNG. Saving the PNG in an external image editor updates a compatible single-texture model without re-importing its GLB. Invalid, partial and wrong-dimension saves show an error while preserving the previous appearance. Press Stop or close/switch the viewer to release watchers.

Differences from original draft

• Bounded input: maximum 32 MiB PNG snapshots, fixed-size reads with file-size/mtime consistency checks, dimension cap 8192².
• Scoped capability: renderer cannot specify arbitrary file paths; an OS-picked file is bound to the owning Electron webContents. Watchers clean up on owner destruction and app quit.
• Safety: reject symlinked watched files and unsupported formats, debounce rename/save bursts, retry partial saves, and ignore stale revisions / async texture loads.
• GPU lifecycle: restore original material maps on panel unmount, dispose replaced GPU textures only after updating references, and preserve original color space/filter/UV sampling rather than globally forcing pixelated textures.
• Add watcher, preload/API and Three.js helper regression tests. Extend the staging CI to Linux and Windows for this branch.
• Leave unrelated Carry artist intent through generated assets lightningpixel/modly#252 UI zoom and artist-intent automation changes out of this PR.

Validation

• Changes isolated to a child branch stacked on DRAFT: explicit v1 Artist Context workflow node (first part of #252) #6.
• Test cases added for corrupt/partial PNGs and recovery, watch stop, symlink/size/dimension limits, IPC scope, multiple materials and restoration.
• Linux and Windows GitHub Actions full gates (running at PR creation).
• Manual Windows Electron run with real Blender/Krita/GIMP external saves; check multiple model switches and GPU resource cleanup.
• Review atomic-save handling, large images, PNG decoding and source-author attribution.

Full technical ledger: docs/experimental-live-texture.md.

Draft; do not merge or describe as a validated installer yet.