fix(translator): correct thought signatures for AG, Gemini CLI, Vertex; fix missing Vertex response translator

- Add DEFAULT_THINKING_AG_SIGNATURE, DEFAULT_THINKING_GEMINI_CLI_SIGNATURE, DEFAULT_THINKING_VERTEX_SIGNATURE
- Rename DEFAULT_THINKING_GEMINI_SIGNATURE → DEFAULT_THINKING_AG_SIGNATURE for clarity
- Pass provider-specific signature into openaiToGeminiBase (AG vs Gemini CLI)
- Replace synthetic thoughtSignatures with Vertex-native signature in postProcessForVertex
- Register Vertex → OpenAI response translator (fixes empty Vertex streaming responses)

Made-with: Cursor

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

@@ -1,29 +1,25 @@
 import { register } from "../index.js";
 import { FORMATS } from "../formats.js";
 import { openaiToGeminiRequest } from "./openai-to-gemini.js";
+import { DEFAULT_THINKING_VERTEX_SIGNATURE } from "../../config/defaultThinkingSignature.js";
 
 /**
  * Post-process a Gemini-format body for Vertex AI compatibility:
  *
- * 1. Strip `id` from every `functionCall` and `functionResponse` part.
- *    Vertex AI rejects requests that include these fields.
- *
- * 2. Strip synthetic `thoughtSignature` parts injected by the base translator.
- *    Vertex rejects fake thought signatures in multi-turn tool-call history;
- *    only real signatures emitted by Vertex itself should be replayed.
+ * 1. Replace all synthetic thoughtSignatures with Vertex-native signature.
+ * 2. Strip `id` from functionCall and functionResponse (Vertex rejects these).
  */
-function stripVertexIncompatibleFields(body) {
+function postProcessForVertex(body) {
   if (!body?.contents) return body;
 
   for (const turn of body.contents) {
     if (!Array.isArray(turn.parts)) continue;
 
-    // Remove standalone synthetic thoughtSignature parts (text === "" with thoughtSignature)
-    turn.parts = turn.parts.filter(
-      p => !(p.thoughtSignature !== undefined && p.text === "" && !p.thought)
-    );
-
     for (const part of turn.parts) {
+      // Replace any synthetic signature with Vertex-native one
+      if (part.thoughtSignature !== undefined) {
+        part.thoughtSignature = DEFAULT_THINKING_VERTEX_SIGNATURE;
+      }
       // Strip id from functionCall
       if (part.functionCall && "id" in part.functionCall) {
         delete part.functionCall.id;
@@ -32,10 +28,6 @@ function stripVertexIncompatibleFields(body) {
       if (part.functionResponse && "id" in part.functionResponse) {
         delete part.functionResponse.id;
       }
-      // Strip thoughtSignature injected alongside functionCall (synthetic signature)
-      if (part.functionCall && "thoughtSignature" in part) {
-        delete part.thoughtSignature;
-      }
     }
   }
 
@@ -44,7 +36,7 @@ function stripVertexIncompatibleFields(body) {
 
 export function openaiToVertexRequest(model, body, stream, credentials) {
   const gemini = openaiToGeminiRequest(model, body, stream, credentials);
-  return stripVertexIncompatibleFields(gemini);
+  return postProcessForVertex(gemini);
 }
 
 register(FORMATS.OPENAI, FORMATS.VERTEX, openaiToVertexRequest, null);