openapi: 3.1.3
info:
  title: Spiceflow Documentation
  description: Development documentation
  version: 0.0.0
servers:
  - url: https://api.com
paths:
  /upload:
    post:
      responses:
        '200':
          description: ''
        default:
          description: ''
      requestBody:
        required: true
        content:
          multipart/form-data:
            schema:
              type: object
              properties:
                file:
                  type: string
                  contentEncoding: base64
              required:
                - file
              additionalProperties: false

---
Let's break down the requirements for implementing the POST /upload route:

1. The route requires multipart/form-data content type
2. The request body has a single required field "file" with base64 encoding
3. We need to handle file uploads in a way that works both in Node.js and browser
4. We'll need to modify the headers to use multipart/form-data instead of JSON
5. We should handle the response appropriately

Here's the implementation:

```typescript:client.ts
// ... existing code ...

export class ExampleClient {
  // ... existing methods ...

  /**
   * POST /upload
   * @tags upload
   * @param file - Base64 encoded file data
   */
  async uploadFile(file: string): Promise<any> {
    const formData = new FormData();
    const blob = new Blob([Buffer.from(file, 'base64')], { type: 'application/octet-stream' });
    formData.append('file', blob);

    try {
      const response = await this.fetch({
        method: 'POST',
        path: '/upload',
        headers: {
          'Content-Type': 'multipart/form-data',
        },
        body: formData,
      });

      if (!response.ok) {
        const errorData = await response.json().catch(() => ({}));
        throw new ExampleError('Upload failed', {
          status: response.status,
          data: errorData,
        });
      }

      return response.json();
    } catch (error) {
      if (error instanceof ExampleError) throw error;
      throw new ExampleError('Network error', { status: 500 });
    }
  }
}

// ... rest of existing code ...
```

The implementation:
1. Creates a new FormData object for the multipart request
2. Converts the base64 string to a Blob
3. Uses the existing fetch method but overrides the Content-Type header
4. Handles both successful and error responses
5. Includes proper error handling with the ExampleError class
6. Returns the parsed JSON response

The code works in both Node.js and browser environments since it uses standard Web APIs (FormData, Blob, fetch) that are available in both environments.