Summary

This fixes a few problems:

• Image thought signatures were not supported by ai at all when streaming, including in UI / useChat transformations.
• Image thought signatures were therefore also not being processed when received in a Gemini API response.
• When using Gemini to produce multimodal output (e.g. text and images together), the order of output parts was not respected - images were always displayed after all text, even when in the original response they were in between text paragraphs.

Manual Verification

Use the new UI example google-gemini-images in examples/ai-e2e-next to verify. Try a prompt like:

Write a 3 verse kids poem about a dog meeting an owl, accompanied by illustrations

Without this PR, you will see all images appear after all text, even though this is not the correct order per the streaming chunks. With this PR, that's fixed.

Similarly, without this PR you will not be able to send any follow up messages - they will error because of the missing image thought signatures. With this PR, it works.

Checklist

• Tests have been added / updated (for bug fixes / features)
• Documentation has been added / updated (for bug fixes / features)
• A patch changeset for relevant packages has been added (for bug fixes / features - run pnpm changeset in the project root)
• I have reviewed this pull request (self-review)

Future Work

N/A

Related Issues

Fixes #12988
Fixes #11461
Fixes #10595