Merge dc07aaa1f5 into 7adbfec2a4

src/api/transform/__tests__/gemini-format.spec.ts

@@ -107,7 +107,7 @@ describe("convertAnthropicMessageToGemini", () => {
 		expect(() => convertAnthropicMessageToGemini(anthropicMessage)).toThrow("Unsupported image source type")
 	})
 
-	it("should convert a message with tool use", () => {
+	it("should convert a message with tool use (no thought signature in history)", () => {
 		const anthropicMessage: Anthropic.Messages.MessageParam = {
 			role: "assistant",
 			content: [
@@ -133,7 +133,40 @@ describe("convertAnthropicMessageToGemini", () => {
 							name: "calculator",
 							args: { operation: "add", numbers: [2, 3] },
 						},
-						thoughtSignature: "skip_thought_signature_validator",
+					},
+				],
+			},
+		])
+	})
+
+	it("should attach thoughtSignature to functionCall when a real signature exists", () => {
+		const anthropicMessage: Anthropic.Messages.MessageParam = {
+			role: "assistant",
+			content: [
+				{ type: "thoughtSignature", thoughtSignature: "real-sig-abc" } as any,
+				{ type: "text", text: "Let me calculate that for you." },
+				{
+					type: "tool_use",
+					id: "calc-123",
+					name: "calculator",
+					input: { operation: "add", numbers: [2, 3] },
+				},
+			],
+		}
+
+		const result = convertAnthropicMessageToGemini(anthropicMessage)
+
+		expect(result).toEqual([
+			{
+				role: "model",
+				parts: [
+					{ text: "Let me calculate that for you." },
+					{
+						functionCall: {
+							name: "calculator",
+							args: { operation: "add", numbers: [2, 3] },
+						},
+						thoughtSignature: "real-sig-abc",
 					},
 				],
 			},

src/api/transform/gemini-format.ts

@@ -41,11 +41,13 @@ export function convertAnthropicContentToGemini(
 
 	// Determine the signature to attach to function calls.
 	// If we're in a mode that expects signatures (includeThoughtSignatures is true):
-	// 1. Use the actual signature if we found one in the history/content.
-	// 2. Fallback to "skip_thought_signature_validator" if missing (e.g. cross-model history).
+	// - Use the actual signature if we found one in the history/content.
+	// - If no real signature exists, omit it (undefined) so the API accepts the request.
+	//   Gemini 3.1+ models reject the synthetic "skip_thought_signature_validator" bypass
+	//   that worked with earlier Gemini 3 models.
 	let functionCallSignature: string | undefined
 	if (includeThoughtSignatures) {
-		functionCallSignature = activeThoughtSignature || "skip_thought_signature_validator"
+		functionCallSignature = activeThoughtSignature
 	}
 
 	if (typeof content === "string") {