feat(google): preserve thought signatures for Gemini 3+ function calling

.changeset/strong-hoops-lick.md

@@ -0,0 +1,5 @@
+---
+'@livekit/agents-plugin-google': minor
+---
+
+preserve thought signatures for Gemini 3+ function calling

agents/src/llm/chat_context.ts

@@ -189,19 +189,35 @@ export class FunctionCall {
 
   createdAt: number;
 
+  /**
+   * Opaque signature for Gemini thinking mode.
+   * When using Gemini 3+ models with thinking enabled, this signature must be
+   * preserved and returned with function responses to maintain thought context.
+   */
+  thoughtSignature?: string;
+
   constructor(params: {
     callId: string;
     name: string;
     args: string;
     id?: string;
     createdAt?: number;
+    thoughtSignature?: string;
   }) {
-    const { callId, name, args, id = shortuuid('item_'), createdAt = Date.now() } = params;
+    const {
+      callId,
+      name,
+      args,
+      id = shortuuid('item_'),
+      createdAt = Date.now(),
+      thoughtSignature,
+    } = params;
     this.id = id;
     this.callId = callId;
     this.args = args;
     this.name = name;
     this.createdAt = createdAt;
+    this.thoughtSignature = thoughtSignature;
   }
 
   static create(params: {
@@ -210,6 +226,7 @@ export class FunctionCall {
     args: string;
     id?: string;
     createdAt?: number;
+    thoughtSignature?: string;
   }) {
     return new FunctionCall(params);
   }
@@ -224,6 +241,10 @@ export class FunctionCall {
       args: this.args,
     };
 
+    if (this.thoughtSignature) {
+      result.thoughtSignature = this.thoughtSignature;
+    }
+
     if (!excludeTimestamp) {
       result.createdAt = this.createdAt;
     }
@@ -602,7 +623,12 @@ export class ChatContext {
           return false;
         }
       } else if (a.type === 'function_call' && b.type === 'function_call') {
-        if (a.name !== b.name || a.callId !== b.callId || a.args !== b.args) {
+        if (
+          a.name !== b.name ||
+          a.callId !== b.callId ||
+          a.args !== b.args ||
+          a.thoughtSignature !== b.thoughtSignature
+        ) {
           return false;
         }
       } else if (a.type === 'function_call_output' && b.type === 'function_call_output') {

agents/src/llm/provider_format/google.ts

@@ -67,13 +67,17 @@ export async function toChatCtx(
         }
       }
     } else if (msg.type === 'function_call') {
-      parts.push({
+      const functionCallPart: Record<string, unknown> = {
         functionCall: {
           id: msg.callId,
           name: msg.name,
           args: JSON.parse(msg.args || '{}'),
         },
-      });
+      };
+      if (msg.thoughtSignature) {
+        functionCallPart.thoughtSignature = msg.thoughtSignature;
+      }
+      parts.push(functionCallPart);
     } else if (msg.type === 'function_call_output') {
       const response = msg.isError ? { error: msg.output } : { output: msg.output };
       parts.push({

agents/src/voice/generation.ts

@@ -442,6 +442,8 @@ export function performLLMInference(
                 callId: `${data.id}/fnc_${data.generatedToolCalls.length}`,
                 name: tool.name,
                 args: tool.args,
+                // Preserve thought signature for Gemini 3+ thinking mode
+                thoughtSignature: tool.thoughtSignature,
               });
 
               data.generatedToolCalls.push(toolCall);

plugins/google/package.json

@@ -43,7 +43,7 @@
     "typescript": "^5.0.0"
   },
   "dependencies": {
-    "@google/genai": "^1.13.0",
+    "@google/genai": "^1.34.0",
     "@livekit/mutex": "^1.1.1",
     "@types/json-schema": "^7.0.15",
     "json-schema": "^0.4.0"

plugins/google/src/llm.ts

@@ -449,6 +449,8 @@ export class LLMStream extends llm.LLMStream {
               callId: part.functionCall.id || shortuuid('function_call_'),
               name: part.functionCall.name!,
               args: JSON.stringify(part.functionCall.args!),
+              // Preserve thought signature for Gemini 3+ thinking mode
+              thoughtSignature: part.thoughtSignature,
             }),
           ],
         },