fix(harness): use type 'image' and mimeType for image parts in convertToHarnessMessage (#13917)

Co-authored-by: Ward Peeters <ward@coding-tech.com>

Author: nancysangani

.changeset/tiny-poems-open.md

@@ -0,0 +1,5 @@
+---
+'@mastra/core': patch
+---
+
+fix(harness): use type 'image' and mimeType for image parts in convertToHarnessMessage to fix Gemini image recognition

packages/core/src/harness/harness.ts

@@ -1740,9 +1740,9 @@ export class Harness<TState = {}> {
                 ? (part as { image?: string }).image!
                 : '';
           content.push({
-            type: 'file',
+            type: 'image',
             data: imgData,
-            mediaType:
+            mimeType:
               (part as { mimeType?: string }).mimeType ?? (part as { mediaType?: string }).mediaType ?? 'image/png',
           });
           break;