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-gemini.js

@@ -1,6 +1,6 @@
 import { register } from "../index.js";
 import { FORMATS } from "../formats.js";
-import { DEFAULT_THINKING_GEMINI_SIGNATURE } from "../../config/defaultThinkingSignature.js";
+import { DEFAULT_THINKING_AG_SIGNATURE, DEFAULT_THINKING_GEMINI_CLI_SIGNATURE } from "../../config/defaultThinkingSignature.js";
 import { ANTIGRAVITY_DEFAULT_SYSTEM } from "../../config/appConstants.js";
 import { openaiToClaudeRequestForAntigravity } from "./openai-to-claude.js";
 
@@ -36,7 +36,7 @@ function sanitizeGeminiFunctionName(name) {
 }
 
 // Core: Convert OpenAI request to Gemini format (base for all variants)
-function openaiToGeminiBase(model, body, stream) {
+function openaiToGeminiBase(model, body, stream, signature = DEFAULT_THINKING_AG_SIGNATURE) {
   const result = {
     model: model,
     contents: [],
@@ -109,7 +109,7 @@ function openaiToGeminiBase(model, body, stream) {
             text: msg.reasoning_content
           });
           parts.push({
-            thoughtSignature: DEFAULT_THINKING_GEMINI_SIGNATURE,
+            thoughtSignature: signature,
             text: ""
           });
         }
@@ -128,7 +128,7 @@ function openaiToGeminiBase(model, body, stream) {
 
             const args = tryParseJSON(tc.function?.arguments || "{}");
             parts.push({
-              thoughtSignature: DEFAULT_THINKING_GEMINI_SIGNATURE,
+              thoughtSignature: signature,
               functionCall: {
                 id: tc.id,
                 name: sanitizeGeminiFunctionName(tc.function.name),
@@ -227,7 +227,7 @@ export function openaiToGeminiRequest(model, body, stream) {
 
 // OpenAI -> Gemini CLI (Cloud Code Assist)
 export function openaiToGeminiCLIRequest(model, body, stream) {
-  const gemini = openaiToGeminiBase(model, body, stream);
+  const gemini = openaiToGeminiBase(model, body, stream, DEFAULT_THINKING_GEMINI_CLI_SIGNATURE);
   const isClaude = model.toLowerCase().includes("claude");
 
   // Add thinking config for CLI