fix: strip functionCall/functionResponse id and synthetic thoughtSignature for Vertex AI (closes #388) (#414)

open-sse/config/providers.js

@@ -303,7 +303,7 @@ export const PROVIDERS = {
   // baseUrl is not used; VertexExecutor.buildUrl() constructs it dynamically
   vertex: {
     baseUrl: "https://aiplatform.googleapis.com",
-    format: "gemini"
+    format: "vertex"
   },
   // Vertex AI - Partner models (Claude, Llama, Mistral, GLM) via SA JSON
   // Uses OpenAI-compatible global endpoint (or rawPredict for Anthropic)

open-sse/handlers/chatCore/nonStreamingHandler.js

@@ -15,7 +15,7 @@ export function translateNonStreamingResponse(responseBody, targetFormat, source
   if (targetFormat === sourceFormat || targetFormat === FORMATS.OPENAI) return responseBody;
 
   // Gemini / Antigravity
-  if (targetFormat === FORMATS.GEMINI || targetFormat === FORMATS.ANTIGRAVITY || targetFormat === FORMATS.GEMINI_CLI) {
+  if (targetFormat === FORMATS.GEMINI || targetFormat === FORMATS.ANTIGRAVITY || targetFormat === FORMATS.GEMINI_CLI || targetFormat === FORMATS.VERTEX) {
     const response = responseBody.response || responseBody;
     if (!response?.candidates?.[0]) return responseBody;
 

open-sse/translator/formats.js

@@ -6,6 +6,7 @@ export const FORMATS = {
   CLAUDE: "claude",
   GEMINI: "gemini",
   GEMINI_CLI: "gemini-cli",
+  VERTEX: "vertex",
   CODEX: "codex",
   ANTIGRAVITY: "antigravity",
   KIRO: "kiro",

open-sse/translator/index.js

@@ -32,6 +32,7 @@ function ensureInitialized() {
   require("./request/openai-to-claude.js");
   require("./request/gemini-to-openai.js");
   require("./request/openai-to-gemini.js");
+  require("./request/openai-to-vertex.js");
   require("./request/antigravity-to-openai.js");
   require("./request/openai-responses.js");
   require("./request/openai-to-kiro.js");

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

@@ -0,0 +1,50 @@
+import { register } from "../index.js";
+import { FORMATS } from "../formats.js";
+import { openaiToGeminiRequest } from "./openai-to-gemini.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.
+ */
+function stripVertexIncompatibleFields(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) {
+      // Strip id from functionCall
+      if (part.functionCall && "id" in part.functionCall) {
+        delete part.functionCall.id;
+      }
+      // Strip id from functionResponse
+      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;
+      }
+    }
+  }
+
+  return body;
+}
+
+export function openaiToVertexRequest(model, body, stream, credentials) {
+  const gemini = openaiToGeminiRequest(model, body, stream, credentials);
+  return stripVertexIncompatibleFields(gemini);
+}
+
+register(FORMATS.OPENAI, FORMATS.VERTEX, openaiToVertexRequest, null);

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

@@ -237,4 +237,5 @@ export function geminiToOpenAIResponse(chunk, state) {
 register(FORMATS.GEMINI, FORMATS.OPENAI, null, geminiToOpenAIResponse);
 register(FORMATS.GEMINI_CLI, FORMATS.OPENAI, null, geminiToOpenAIResponse);
 register(FORMATS.ANTIGRAVITY, FORMATS.OPENAI, null, geminiToOpenAIResponse);
+register(FORMATS.VERTEX, FORMATS.OPENAI, null, geminiToOpenAIResponse);