fix(translator): strip function_call.id for Vertex AI provider (#3440) (#3457)

Vertex AI's FunctionCall/FunctionResponse protos have no id field; emitting it made Vertex reject tool calls with 400 'Unknown name id'. The id is now stripped only when the routed provider is vertex/vertex-partner (threaded via credentials._provider), preserving it for the public Gemini API where Gemini 3+ uses it for signature matching.

Co-authored-by: nullbytef0x <nullbytef0x@users.noreply.github.com>

CHANGELOG.md

@@ -8,6 +8,10 @@
 
 _Development cycle in progress — entries are added as work merges into `release/v3.8.17` and finalized by the release flow._
 
+### 🔧 Bug Fixes
+
+- **fix(translator):** Vertex AI tool calls no longer fail with `400 Unknown name "id" at contents[].parts[].function_call` — the OpenAI-style `id` field is now stripped from `functionCall`/`functionResponse` parts when the routed provider is `vertex`/`vertex-partner`. The public Gemini API still receives `id` (required for Gemini 3+ signature matching). ([#3440](https://github.com/diegosouzapw/OmniRoute/issues/3440) — thanks @nullbytef0x)
+
 ---
 
 ## [3.8.16] — 2026-06-08

open-sse/translator/index.ts

@@ -175,7 +175,13 @@ export function translateRequest(
     // Check for direct translation path first (e.g., Claude → Gemini)
     const directTranslator = getRequestTranslator(sourceFormat, targetFormat);
     if (directTranslator && sourceFormat !== FORMATS.OPENAI && targetFormat !== FORMATS.OPENAI) {
-      result = directTranslator(model, result, stream, credentials);
+      // Thread the routed provider id so target translators can apply provider-specific
+      // quirks (e.g. Vertex rejects function_call.id — #3440).
+      const directCredentials =
+        provider != null
+          ? { ...(credentials && typeof credentials === "object" ? credentials : {}), _provider: provider }
+          : credentials;
+      result = directTranslator(model, result, stream, directCredentials);
     } else {
       // Fallback: hub-and-spoke via OpenAI
       // Step 1: source -> openai (if source is not openai)
@@ -205,13 +211,17 @@ export function translateRequest(
           const hasNs = options?.signatureNamespace != null;
           const hasPreCompression = options?.preCompressionBody != null;
           const hasCopilot = options?.copilotClient === true;
+          const hasProvider = provider != null;
           const translationCredentials =
-            hasNs || hasPreCompression || hasCopilot
+            hasNs || hasPreCompression || hasCopilot || hasProvider
               ? {
                   ...(credentials && typeof credentials === "object" ? credentials : {}),
                   ...(hasNs ? { _signatureNamespace: options.signatureNamespace } : {}),
                   ...(hasPreCompression ? { _preCompressionBody: options.preCompressionBody } : {}),
                   ...(hasCopilot ? { _copilotClient: true } : {}),
+                  // Routed provider id so target translators can apply provider-specific
+                  // quirks (e.g. Vertex rejects function_call.id — #3440).
+                  ...(hasProvider ? { _provider: provider } : {}),
                 }
               : credentials;
           result = fromOpenAI(model, result, stream, translationCredentials);

open-sse/translator/request/claude-to-gemini.ts

@@ -14,12 +14,17 @@ import { capMaxOutputTokens } from "../../../src/lib/modelCapabilities.ts";
  * Converts Claude Messages API body directly to Gemini format,
  * skipping the OpenAI hub intermediate step.
  */
-export function claudeToGeminiRequest(model, body, stream) {
+export function claudeToGeminiRequest(model, body, stream, credentials = null) {
   const toolNameMap = new Map<string, string>();
   const sanitizeToolName = (name: string) =>
     sanitizeGeminiToolName(name, {
       toolNameMap,
     });
+  // Vertex AI rejects the `id` field inside function_call / function_response parts
+  // (#3440). The public Gemini API keeps it for Gemini 3+ signature matching, so this
+  // is scoped to the routed vertex provider only (threaded via credentials._provider).
+  const provider = credentials && typeof credentials === "object" ? credentials._provider : null;
+  const stripFunctionCallId = provider === "vertex" || provider === "vertex-partner";
   const result: {
     model: string;
     contents: Array<Record<string, unknown>>;
@@ -105,7 +110,7 @@ export function claudeToGeminiRequest(model, body, stream) {
             case "tool_use":
               parts.push({
                 functionCall: {
-                  id: block.id,
+                  ...(stripFunctionCallId ? {} : { id: block.id }),
                   name: sanitizeToolName(block.name),
                   args: block.input || {},
                 },
@@ -127,7 +132,7 @@ export function claudeToGeminiRequest(model, body, stream) {
               }
               parts.push({
                 functionResponse: {
-                  id: block.tool_use_id,
+                  ...(stripFunctionCallId ? {} : { id: block.tool_use_id }),
                   name: toolUseNames[block.tool_use_id] || "unknown",
                   response: { result: parsedContent },
                 },

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

@@ -109,8 +109,19 @@ type GeminiToolNameOptions = {
   functionResponseShape?: "result" | "output";
   signatureNamespace?: string | null;
   signaturelessToolCallMode?: "native" | "text" | "context";
+  // Vertex AI's FunctionCall/FunctionResponse protos have no `id` field; emitting it
+  // makes Vertex reject the request with 400 "Unknown name id" (#3440). The public
+  // Gemini API DOES use `id` for Gemini 3+ signature matching, so this is scoped to
+  // the vertex provider only.
+  stripFunctionCallId?: boolean;
 };
 
+// Vertex AI (and Vertex Partner models) reject the OpenAI-style `id` field inside
+// function_call / function_response parts. Detect these by the routed provider id.
+function isVertexGeminiProvider(provider: unknown): boolean {
+  return provider === "vertex" || provider === "vertex-partner";
+}
+
 type OpenAIToolCallLike = {
   thoughtSignature?: unknown;
   thought_signature?: unknown;
@@ -430,7 +441,7 @@ function openaiToGeminiBase(
             parts.push({
               ...(embeddedThoughtSignature ? { thoughtSignature: embeddedThoughtSignature } : {}),
               functionCall: {
-                id: id,
+                ...(toolNameOptions.stripFunctionCallId ? {} : { id: id }),
                 name: sanitizeToolName(fn.name),
                 args: args,
               },
@@ -482,7 +493,7 @@ function openaiToGeminiBase(
 
               toolParts.push({
                 functionResponse: {
-                  id: fid,
+                  ...(toolNameOptions.stripFunctionCallId ? {} : { id: fid }),
                   name: name,
                   response:
                     toolNameOptions.functionResponseShape === "output"
@@ -605,6 +616,7 @@ export function openaiToGeminiRequest(
   return openaiToGeminiBase(model, body, stream, {
     signatureNamespace,
     signaturelessToolCallMode: options.signaturelessToolCallMode,
+    stripFunctionCallId: isVertexGeminiProvider(credentials?._provider),
   });
 }
 

tests/unit/vertex-functioncall-id-3440.test.ts

@@ -0,0 +1,143 @@
+// Regression test for #3440 — Vertex AI rejects tool calls because OmniRoute
+// emits an `id` field inside `function_call` / `function_response` parts.
+//
+// Vertex AI (aiplatform.googleapis.com) follows an older Gemini REST schema whose
+// FunctionCall/FunctionResponse protos have no `id` field, so it returns
+// `400 INVALID_ARGUMENT: Unknown name "id" at 'contents[].parts[].function_call'`.
+// The public Gemini API (generativelanguage.googleapis.com) DOES use `id` for
+// Gemini 3+ signature matching, so the strip must be scoped to the vertex provider
+// only (threaded via credentials._provider), never applied unconditionally.
+
+import test from "node:test";
+import assert from "node:assert/strict";
+
+const { openaiToGeminiRequest } = await import(
+  "../../open-sse/translator/request/openai-to-gemini.ts"
+);
+const { claudeToGeminiRequest } = await import(
+  "../../open-sse/translator/request/claude-to-gemini.ts"
+);
+
+type UnknownRecord = Record<string, unknown>;
+
+function findFunctionCall(result: any): UnknownRecord | undefined {
+  for (const content of result.contents ?? []) {
+    for (const part of content.parts ?? []) {
+      if (part?.functionCall) return part.functionCall as UnknownRecord;
+    }
+  }
+  return undefined;
+}
+
+function findFunctionResponse(result: any): UnknownRecord | undefined {
+  for (const content of result.contents ?? []) {
+    for (const part of content.parts ?? []) {
+      if (part?.functionResponse) return part.functionResponse as UnknownRecord;
+    }
+  }
+  return undefined;
+}
+
+const OPENAI_TOOL_BODY = {
+  messages: [
+    { role: "user", content: "What's the weather?" },
+    {
+      role: "assistant",
+      content: null,
+      tool_calls: [
+        {
+          id: "call_weather_1",
+          type: "function",
+          function: { name: "get_weather", arguments: '{"city":"Tokyo"}' },
+        },
+      ],
+    },
+    { role: "tool", tool_call_id: "call_weather_1", content: '{"temp":20}' },
+  ],
+  tools: [
+    {
+      type: "function",
+      function: {
+        name: "get_weather",
+        description: "Get weather",
+        parameters: {
+          type: "object",
+          properties: { city: { type: "string" } },
+          required: ["city"],
+        },
+      },
+    },
+  ],
+};
+
+const CLAUDE_TOOL_BODY = {
+  messages: [
+    { role: "user", content: "What's the weather?" },
+    {
+      role: "assistant",
+      content: [
+        { type: "tool_use", id: "tu_weather_1", name: "get_weather", input: { city: "Tokyo" } },
+      ],
+    },
+    {
+      role: "user",
+      content: [{ type: "tool_result", tool_use_id: "tu_weather_1", content: '{"temp":20}' }],
+    },
+  ],
+};
+
+test("#3440 OpenAI->Gemini: vertex provider omits id from functionCall and functionResponse", () => {
+  const result = openaiToGeminiRequest("gemini-2.5-pro", OPENAI_TOOL_BODY, false, {
+    _provider: "vertex",
+  });
+
+  const fc = findFunctionCall(result);
+  assert.ok(fc, "expected a functionCall part");
+  assert.equal(fc.id, undefined, "functionCall.id must be omitted for Vertex");
+  assert.equal(fc.name, "get_weather");
+
+  const fr = findFunctionResponse(result);
+  assert.ok(fr, "expected a functionResponse part");
+  assert.equal(fr.id, undefined, "functionResponse.id must be omitted for Vertex");
+});
+
+test("#3440 OpenAI->Gemini: vertex-partner provider also omits id", () => {
+  const result = openaiToGeminiRequest("gemini-2.5-pro", OPENAI_TOOL_BODY, false, {
+    _provider: "vertex-partner",
+  });
+  assert.equal(findFunctionCall(result)?.id, undefined);
+  assert.equal(findFunctionResponse(result)?.id, undefined);
+});
+
+test("#3440 OpenAI->Gemini: public gemini provider PRESERVES id (Gemini 3+ signature matching)", () => {
+  const result = openaiToGeminiRequest("gemini-2.5-pro", OPENAI_TOOL_BODY, false, {
+    _provider: "gemini",
+  });
+  assert.equal(
+    findFunctionCall(result)?.id,
+    "call_weather_1",
+    "functionCall.id must be preserved for the public Gemini API"
+  );
+});
+
+test("#3440 OpenAI->Gemini: no provider hint PRESERVES id (default, non-vertex)", () => {
+  const result = openaiToGeminiRequest("gemini-2.5-pro", OPENAI_TOOL_BODY, false, null);
+  assert.equal(findFunctionCall(result)?.id, "call_weather_1");
+});
+
+test("#3440 Claude->Gemini: vertex provider omits id from functionCall and functionResponse", () => {
+  const result = claudeToGeminiRequest("gemini-2.5-pro", CLAUDE_TOOL_BODY, false, {
+    _provider: "vertex",
+  });
+  assert.equal(findFunctionCall(result)?.id, undefined, "functionCall.id must be omitted for Vertex");
+  assert.equal(
+    findFunctionResponse(result)?.id,
+    undefined,
+    "functionResponse.id must be omitted for Vertex"
+  );
+});
+
+test("#3440 Claude->Gemini: no provider hint PRESERVES id (default, non-vertex)", () => {
+  const result = claudeToGeminiRequest("gemini-2.5-pro", CLAUDE_TOOL_BODY, false);
+  assert.equal(findFunctionCall(result)?.id, "tu_weather_1");
+});