fix(gemini): strip data URI prefix from PDF base64 data

[404-Page-Found]

What this PR does

Before this PR:
Uploading a PDF file and sending it to Gemini-3.1-pro-preview (or other Gemini models via certain proxies) failed with a "Base64 decoding failed" error because the payload incorrectly included the data:application/pdf;base64, prefix.

After this PR:
The application correctly strips the Data URI prefix from the base64 data for PDF files, ensuring only the raw base64 string is sent to the API.

Fixes #14097

Why we need it and why it was done in this way

Certain API proxies or specific model versions are stricter about the inline_data.data format and do not handle the Data URI prefix. Stripping it ensures compatibility across different providers while remaining compliant with the expected standard of raw base64 for these fields.

The following tradeoffs were made:

• Added a simple regex check to strip the prefix if present. This adds a negligible overhead but significantly improves compatibility.

The following alternatives were considered:

• Modifying the backend to handle the prefix, but since this is a frontend-to-SDK interaction, fixing it at the source of parameter preparation is more direct and robust.

Breaking changes

None.

Special notes for your reviewer

I've verified that base64File returns raw base64 in FileStorage.ts, but added this defensive check in fileProcessor.ts to ensure that any data passed to the AI SDK is clean.

Checklist

• PR: The PR description is expressive enough and will help future contributors
• Code: Write code that humans can understand and Keep it simple
• Refactor: You have left the code cleaner than you found it (Boy Scout Rule)
• Upgrade: Impact of this change on upgrade flows was considered and addressed if required
• Documentation: A user-guide update was considered and is present (link) or not required. Check this only when the PR introduces or changes a user-facing feature or behavior.
• Self-review: I have reviewed my own code (e.g., via /gh-pr-review, gh pr diff, or GitHub UI) before requesting review from others

Release note

Fixed an issue where PDF file uploads to Gemini models failed due to incorrect Base64 encoding format.

[DeJeune]

Note

This issue/comment/review was translated by Claude.

It can be merged to v1, please revise the PR according to the guidelines.

---

Original Content

可以合并到v1，根据规范重新改一下pr

[404-Page-Found]

Note

This issue/comment/review was translated by Claude.

New PR URL
PR #14134

---

Original Content

新PR网址
PR #14134