fix(ai): avoid unsigned Gemini 3 tool calls (#741)

packages/ai/src/providers/google-shared.ts

@@ -131,18 +131,29 @@ export function convertMessages<T extends GoogleApiType>(model: Model<T>, contex
 						});
 					}
 				} else if (block.type === "toolCall") {
-					const part: Part = {
-						functionCall: {
-							name: block.name,
-							args: block.arguments,
-							...(requiresToolCallId(model.id) ? { id: block.id } : {}),
-						},
-					};
 					const thoughtSignature = resolveThoughtSignature(isSameProviderAndModel, block.thoughtSignature);
-					if (thoughtSignature) {
-						part.thoughtSignature = thoughtSignature;
+					// Gemini 3 requires thoughtSignature on all function calls when thinking mode is enabled.
+					// When replaying history from providers without thought signatures (e.g. Claude via Antigravity),
+					// convert unsigned function calls to text to avoid API validation errors.
+					const isGemini3 = model.id.toLowerCase().includes("gemini-3");
+					if (isGemini3 && !thoughtSignature) {
+						const argsStr = JSON.stringify(block.arguments, null, 2);
+						parts.push({
+							text: `[Tool Call: ${block.name}]\nArguments: ${argsStr}`,
+						});
+					} else {
+						const part: Part = {
+							functionCall: {
+								name: block.name,
+								args: block.arguments,
+								...(requiresToolCallId(model.id) ? { id: block.id } : {}),
+							},
+						};
+						if (thoughtSignature) {
+							part.thoughtSignature = thoughtSignature;
+						}
+						parts.push(part);
 					}
-					parts.push(part);
 				}
 			}
 

packages/ai/test/google-shared-gemini3-unsigned-tool-call.test.ts

@@ -0,0 +1,69 @@
+import { describe, expect, it } from "vitest";
+import { convertMessages } from "../src/providers/google-shared.js";
+import type { Context, Model } from "../src/types.js";
+
+describe("google-shared convertMessages", () => {
+	it("converts unsigned tool calls to text for Gemini 3", () => {
+		const model: Model<"google-generative-ai"> = {
+			id: "gemini-3-pro-preview",
+			name: "Gemini 3 Pro Preview",
+			api: "google-generative-ai",
+			provider: "google",
+			baseUrl: "https://generativelanguage.googleapis.com",
+			reasoning: true,
+			input: ["text"],
+			cost: { input: 0, output: 0, cacheRead: 0, cacheWrite: 0 },
+			contextWindow: 128000,
+			maxTokens: 8192,
+		};
+
+		const now = Date.now();
+		const context: Context = {
+			messages: [
+				{ role: "user", content: "Hi", timestamp: now },
+				{
+					role: "assistant",
+					content: [
+						{
+							type: "toolCall",
+							id: "call_1",
+							name: "bash",
+							arguments: { command: "ls -la" },
+							// No thoughtSignature: simulates Claude via Antigravity.
+						},
+					],
+					api: "google-gemini-cli",
+					provider: "google-antigravity",
+					model: "claude-sonnet-4-20250514",
+					usage: {
+						input: 0,
+						output: 0,
+						cacheRead: 0,
+						cacheWrite: 0,
+						totalTokens: 0,
+						cost: { input: 0, output: 0, cacheRead: 0, cacheWrite: 0, total: 0 },
+					},
+					stopReason: "stop",
+					timestamp: now,
+				},
+			],
+		};
+
+		const contents = convertMessages(model, context);
+
+		let toolTurn: (typeof contents)[number] | undefined;
+		for (let i = contents.length - 1; i >= 0; i -= 1) {
+			if (contents[i]?.role === "model") {
+				toolTurn = contents[i];
+				break;
+			}
+		}
+
+		expect(toolTurn).toBeTruthy();
+		expect(toolTurn?.parts?.some((p) => p.functionCall !== undefined)).toBe(false);
+
+		const text = toolTurn?.parts?.map((p) => p.text ?? "").join("\n");
+		expect(text).toContain("[Tool Call: bash]");
+		expect(text).toContain("ls -la");
+	});
+});