refactor(translator): P4 concern #2 encodeDataUri — dedupe base64 data-uri building

- imageHelper.encodeDataUri(mime, base64) replaces 5 inline `data:${m};base64,${d}` templates
- Applied to gemini/claude/antigravity request + gemini response translators
- Golden tests pass, identical output

Co-authored-by: Cursor <cursoragent@cursor.com>

open-sse/translator/helpers/imageHelper.js

@@ -1,3 +1,8 @@
+// Build a base64 data URI from mime + base64 payload
+export function encodeDataUri(mimeType, base64) {
+  return `data:${mimeType};base64,${base64}`;
+}
+
 /**
  * Fetch a remote image URL and return it as a base64 data URI.
  * Used when upstream providers (Codex, etc.) require inline base64 images

open-sse/translator/request/antigravity-to-openai.js

@@ -1,6 +1,7 @@
 import { register } from "../index.js";
 import { FORMATS } from "../formats.js";
 import { adjustMaxTokens } from "../helpers/maxTokensHelper.js";
+import { encodeDataUri } from "../helpers/imageHelper.js";
 
 // Convert Antigravity request to OpenAI format
 // Antigravity body: { project, model, userAgent, requestType, requestId, request: { contents, systemInstruction, tools, toolConfig, generationConfig, sessionId } }
@@ -156,7 +157,7 @@ function convertContent(content) {
       textParts.push({
         type: "image_url",
         image_url: {
-          url: `data:${part.inlineData.mimeType};base64,${part.inlineData.data}`
+          url: encodeDataUri(part.inlineData.mimeType, part.inlineData.data)
         }
       });
     }

open-sse/translator/request/claude-to-openai.js

@@ -1,6 +1,7 @@
 import { register } from "../index.js";
 import { FORMATS } from "../formats.js";
 import { adjustMaxTokens } from "../helpers/maxTokensHelper.js";
+import { encodeDataUri } from "../helpers/imageHelper.js";
 
 function stripAnthropicBillingHeader(text) {
   if (typeof text !== "string") return "";
@@ -140,7 +141,7 @@ function convertClaudeMessage(msg) {
             parts.push({
               type: "image_url",
               image_url: {
-                url: `data:${block.source.media_type};base64,${block.source.data}`
+                url: encodeDataUri(block.source.media_type, block.source.data)
               }
             });
           }

open-sse/translator/request/gemini-to-openai.js

@@ -1,6 +1,7 @@
 import { register } from "../index.js";
 import { FORMATS } from "../formats.js";
 import { adjustMaxTokens } from "../helpers/maxTokensHelper.js";
+import { encodeDataUri } from "../helpers/imageHelper.js";
 
 // Convert Gemini request to OpenAI format
 export function geminiToOpenAIRequest(model, body, stream) {
@@ -88,7 +89,7 @@ function convertGeminiContent(content) {
       parts.push({
         type: "image_url",
         image_url: {
-          url: `data:${part.inlineData.mimeType};base64,${part.inlineData.data}`
+          url: encodeDataUri(part.inlineData.mimeType, part.inlineData.data)
         }
       });
     }

open-sse/translator/response/gemini-to-openai.js

@@ -3,6 +3,7 @@ import { FORMATS } from "../formats.js";
 import { buildChunk } from "../helpers/chunkBuilder.js";
 import { buildUsage } from "../helpers/usageHelper.js";
 import { reasoningDelta } from "../helpers/reasoningHelper.js";
+import { encodeDataUri } from "../helpers/imageHelper.js";
 
 // Build chunk meta for current gemini state
 function chunkMeta(state) {
@@ -116,7 +117,7 @@ export function geminiToOpenAIResponse(chunk, state) {
           {
             images: [{
               type: "image_url",
-              image_url: { url: `data:${mimeType};base64,${inlineData.data}` }
+              image_url: { url: encodeDataUri(mimeType, inlineData.data) }
             }]
           },
           null