feat: support new OpenAI file library APIs (selectFiles, uploadFile library option)

[qchuchu]

Context

OpenAI has added new file-related APIs to the Apps SDK:

New API

• window.openai.selectFiles() — opens ChatGPT's file library picker (feature-detect before using) and returns app-authorized files as [{ fileId, fileName, mimeType }].

Modified APIs

• window.openai.uploadFile(file, { library?: boolean }) — now accepts an options object; pass { library: true } to also save the upload into the user's ChatGPT file library when that library is available.
• window.openai.getFileDownloadUrl({ fileId }) — now works for files uploaded by the widget, files selected via selectFiles(), or files provided via tool/file params (previously only uploads or file params).

State management update

• imageIds may include file IDs selected via selectFiles() in addition to uploaded file IDs or file params.

What needs to change in Skybridge

1. Types — Update AppsSdkOpenAI interface to add selectFiles() and the new uploadFile options parameter
2. Adaptor — Update AppsSdkAdaptor to support selectFiles() and forward the library option on uploadFile
3. Hook — Extend useFiles() to expose selectFiles alongside upload and getDownloadUrl
4. Adaptor interface — Update the shared Adaptor interface with the new method + updated signature
5. MCP adaptor — Add selectFiles stub that throws (not supported in MCP Apps)
6. Docs — Update docs/api-reference/use-files.mdx
7. Skills — Update chatgpt-app-builder skill if it references file APIs

Source

Diff from alpic-ai/openai-apps-sdk-docs