OAS 3.1 array items with contentMediaType render as text inputs instead of file pickers

Q&A

• OS: macOS
• Browser: Chrome
• Method of installation: npm
• Swagger-UI version: 5.x (latest)
• Swagger/OpenAPI version: OpenAPI 3.1

Content & configuration

Example Swagger/OpenAPI definition:

openapi: 3.1.0
info:
  title: Example
  version: 1.0.0
paths:
  /upload:
    post:
      requestBody:
        content:
          multipart/form-data:
            schema:
              type: object
              properties:
                files:
                  type: array
                  items:
                    type: string
                    contentMediaType: application/octet-stream

Describe the bug you're encountering

When a multipart/form-data body has an array property whose items use
contentMediaType (the OAS 3.1 / JSON Schema 2020-12 way to declare binary
content), Swagger UI renders plain text inputs instead of "Choose File" buttons.

This is reproducible with FastAPI 0.129.1+, which stopped emitting
format: binary for UploadFile fields in favour of contentMediaType: application/octet-stream to comply with the OAS 3.1 spec.

To reproduce...

1. Serve the YAML above in Swagger UI
2. Open POST /upload and click "Try it out"
3. Click "Add string item"
4. See a plain text input instead of a file picker

Expected behavior

Clicking "Add item" should produce a type="file" input (a "Choose File"
button), consistent with how format: binary array items are handled and
how single-file contentMediaType fields are already handled in
oas31/oas3-extensions/fn.js.

Screenshots

Current (broken):

Expected:

Start in oas31/oas3-extensions/fn.js, where single-file contentMediaType handling is already implemented, and compare it with the array-item path. Reproduce the provided OpenAPI 3.1 multipart example in Swagger UI and verify that adding an item produces a file input rather than a text input.