feat: update input_file data format to include data URL scheme

src/server/routes/proxy/inputFiles.test.ts

@@ -49,7 +49,7 @@ describe('inlineLocalInputFileReferences', () => {
             {
               type: 'input_file',
               filename: 'report.pdf',
-              file_data: Buffer.from('%PDF-demo').toString('base64'),
+              file_data: `data:application/pdf;base64,${Buffer.from('%PDF-demo').toString('base64')}`,
             },
           ],
         },

src/server/routes/proxy/upstreamEndpoint.test.ts

@@ -455,7 +455,7 @@ describe('buildUpstreamEndpointRequest', () => {
         role: 'user',
         content: [
           { type: 'input_text', text: 'summarize this file' },
-          { type: 'input_file', filename: 'brief.pdf', file_data: 'JVBERi0xLjc=' },
+          { type: 'input_file', filename: 'brief.pdf', file_data: 'data:application/pdf;base64,JVBERi0xLjc=' },
         ],
       },
     ]);
@@ -501,7 +501,7 @@ describe('buildUpstreamEndpointRequest', () => {
             type: 'input_file',
             file_id: 'file_local_123',
             filename: 'paper.pdf',
-            file_data: 'JVBERi0xLjQK',
+            file_data: 'data:application/pdf;base64,JVBERi0xLjQK',
           },
         ],
       },
@@ -705,7 +705,7 @@ describe('buildUpstreamEndpointRequest', () => {
           {
             type: 'input_file',
             filename: 'notes.txt',
-            file_data: 'aGVsbG8=',
+            file_data: 'data:text/plain;base64,aGVsbG8=',
           },
         ],
       },

src/server/services/proxyInputFileResolver.test.ts

@@ -71,7 +71,7 @@ describe('proxyInputFileResolver', () => {
             type: 'input_file',
             file_id: 'file-metapi-123',
             filename: 'brief.pdf',
-            file_data: Buffer.from('%PDF-local').toString('base64'),
+            file_data: `data:application/pdf;base64,${Buffer.from('%PDF-local').toString('base64')}`,
           },
         ],
       },

src/server/services/proxyInputFileResolver.ts

@@ -1,5 +1,6 @@
 import type { ProxyResourceOwner } from '../middleware/auth.js';
 import { getProxyFileByPublicIdForOwner, LOCAL_PROXY_FILE_ID_PREFIX } from './proxyFileStore.js';
+import { ensureBase64DataUrl } from '../transformers/shared/inputFile.js';
 
 function isRecord(value: unknown): value is Record<string, unknown> {
   return !!value && typeof value === 'object' && !Array.isArray(value);
@@ -213,7 +214,7 @@ function toResponsesResolvedBlock(file: { fileId?: string; filename: string; fil
     type: 'input_file',
     ...(file.fileId ? { file_id: file.fileId } : {}),
     filename: file.filename,
-    file_data: file.fileData,
+    file_data: ensureBase64DataUrl(file.fileData, file.mimeType),
   };
 }
 

src/server/transformers/openai/responses/conversion.test.ts

@@ -231,7 +231,7 @@ describe('convertOpenAiBodyToResponsesBody', () => {
           {
             type: 'input_file',
             filename: 'notes.md',
-            file_data: Buffer.from('# hello').toString('base64'),
+            file_data: `data:text/markdown;base64,${Buffer.from('# hello').toString('base64')}`,
           },
         ],
       },
@@ -427,7 +427,7 @@ describe('convertOpenAiBodyToResponsesBody', () => {
             type: 'input_file',
             file_id: 'file_local_123',
             filename: 'report.pdf',
-            file_data: 'JVBERi0xLjQK',
+            file_data: 'data:application/pdf;base64,JVBERi0xLjQK',
           },
         ],
       },

src/server/transformers/shared/inputFile.ts

@@ -15,6 +15,16 @@ function splitBase64DataUrl(value: string): { mimeType: string; data: string } |
   };
 }
 
+export function ensureBase64DataUrl(fileData: string, mimeType?: string | null): string {
+  const trimmedData = asTrimmedString(fileData);
+  if (!trimmedData) return trimmedData;
+  if (splitBase64DataUrl(trimmedData)) return trimmedData;
+
+  const normalizedMimeType = asTrimmedString(mimeType).toLowerCase();
+  if (!normalizedMimeType) return trimmedData;
+  return `data:${normalizedMimeType};base64,${trimmedData}`;
+}
+
 export type NormalizedInputFile = {
   sourceType?: 'file' | 'input_file';
   fileId?: string;
@@ -94,7 +104,12 @@ export function toResponsesInputFileBlock(file: NormalizedInputFile): Record<str
   const parsedDataUrl = file.fileData ? splitBase64DataUrl(file.fileData) : null;
   const block: Record<string, unknown> = { type: 'input_file' };
   if (file.fileId) block.file_id = file.fileId;
-  if (file.fileData) block.file_data = parsedDataUrl?.data || file.fileData;
+  if (file.fileData) {
+    block.file_data = ensureBase64DataUrl(
+      file.fileData,
+      parsedDataUrl?.mimeType || inferInputFileMimeType(file),
+    );
+  }
   if (file.filename) block.filename = file.filename;
   return block;
 }