[Draft] Discuss options for exposing original image metadata in upscaled images (Issue #6291)

[Filippo-Venturini]

Summary

This draft PR is meant to continue the discussion from [Issue #6291](https://github.com/InvokeAI/InvokeAI/issues/XXXX) and the related Discord conversation regarding original image metadata for upscaled images.

Currently, upscaled images store a reference to the source image via upscale_initial_image, but the full metadata (prompt, seed, scheduler, etc.) is not stored.

Two alternatives are under discussion:

1. Expose a UI way to jump to the source image in the gallery, leveraging the existing reference.
2. Store the full original metadata under a separate field (e.g., source_image_metadata) for external/export use.

This PR does not include any implementation; it is intended to facilitate review and discussion among maintainers.

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Related Issues / Discussions

• GitHub Issue: [Issue #6291]([bug]: Meta Data Lost With Built-In Upscaler #6291)
• Discord discussion: “I am sure someone will correct me if I am wrong… the biggest question here is what original metadata you keep…”

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QA Instructions

Not applicable — no code changes in this PR.

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Merge Plan

• Marked as draft to indicate discussion PR.
• No merging expected until a consensus on the approach is reached.

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Checklist

• PR title is short but descriptive
• Implementation to be added after discussion
• Documentation updated once implementation is decided