[tiensonqin]

Summary

Expose Backend.NaturalImageSize(id) (width, height float32, ready bool) so desktop adapters can answer natural-size queries for standard image, file-image and avatar nodes without a second decoder or guessed layout dimensions.

The read-only UI-thread query uses current registered images or the current retained state's decoded pixels. URL sources take precedence over registrations; source/decode-limit mismatches, pending work, retired nodes and closed resources return unavailable. Dimensions reflect actual decoded pixels, including max-pixel-size downsampling, not cropping or placeholder sizes. Documents lifecycle and retry semantics in docs/api-migrations.md.

Validated against the pinned MyGo dependency without workspace overrides: gofmt, git diff --check, go test ./..., go test -race ./..., go vet ./..., go build ./... in platform/mygo. No test changes: existing resource lifecycle, source replacement and decode-size contracts cover the underlying state; test-value-gate denied redundant getter tests. No UI-driven testing.

Link to Devin session: https://app.devin.ai/sessions/79843e4449f241f7bef6c8b6b71c5354
Open in Devin Desktop: https://app.devin.ai/desktop/session/79843e4449f241f7bef6c8b6b71c5354?variant=devin
Requested by: @tiensonqin

[devin-ai-integration]

I'll fix CI failures and address comments from users with write access. I'll skip comments containing "(aside)".

• Disable automatic comment, CI, and merge conflict monitoring