Function resolveReferenceMediaSource

resolveReferenceMediaSource(
    source: { base64?: string; mimeType?: string; url?: string },
    defaultMimeType?: string,
    errorMessage?: string,
): ResolvedReferenceMediaSource
Normalizes a reference-media input that may arrive as raw base64, Data URI, or remote URL.
Parameters
- source: { base64?: string; mimeType?: string; url?: string }
  Reference media input with base64, url, and optional mimeType.
- defaultMimeType: string = "image/png"
  Fallback MIME type.
- errorMessage: string = "Reference media input requires base64 or url"
  Error used when no usable media source is present.
Returns ResolvedReferenceMediaSource
Base64 or remote URL representation with MIME type.

Throws
When neither base64 nor url is present.
- Defined in src/core/utils/FileIOUtils.ts:391