fix(ai): correct Gemini tool result format and improve type safety

- Fix tool result format for Gemini 3 Flash Preview compatibility
  - Use 'output' key for successful results (not 'result')
  - Use 'error' key for error results (not 'isError')
  - Per Google SDK documentation for FunctionResponse.response

- Improve type safety in google.ts provider
  - Add ImageContent import and use proper type guards
  - Replace 'as any' casts with proper typing
  - Import and use Schema type for tool parameters
  - Add proper typing for index deletion in error handler

- Add comprehensive test for Gemini 3 Flash tool calling
  - Tests successful tool call and result handling
  - Tests error tool result handling
  - Verifies fix for issue #213

Fixes #213

packages/ai/src/providers/google.ts

@@ -6,6 +6,7 @@ import {
 	type GenerateContentParameters,
 	GoogleGenAI,
 	type Part,
+	type Schema,
 	type ThinkingConfig,
 	type ThinkingLevel,
 } from "@google/genai";
@@ -14,6 +15,7 @@ import type {
 	Api,
 	AssistantMessage,
 	Context,
+	ImageContent,
 	Model,
 	StopReason,
 	StreamFunction,
@@ -238,7 +240,12 @@ export const streamGoogle: StreamFunction<"google-generative-ai"> = (
 			stream.push({ type: "done", reason: output.stopReason, message: output });
 			stream.end();
 		} catch (error) {
-			for (const block of output.content) delete (block as any).index;
+			// Remove internal index property used during streaming
+			for (const block of output.content) {
+				if ("index" in block) {
+					delete (block as { index?: number }).index;
+				}
+			}
 			output.stopReason = options?.signal?.aborted ? "aborted" : "error";
 			output.errorMessage = error instanceof Error ? error.message : JSON.stringify(error);
 			stream.push({ type: "error", reason: output.stopReason, error: output });
@@ -389,33 +396,33 @@ function convertMessages(model: Model<"google-generative-ai">, context: Context)
 			const parts: Part[] = [];
 
 			// Extract text and image content
-			const textResult = msg.content
-				.filter((c) => c.type === "text")
-				.map((c) => (c as any).text)
-				.join("\n");
-			const imageBlocks = model.input.includes("image") ? msg.content.filter((c) => c.type === "image") : [];
+			const textContent = msg.content.filter((c): c is TextContent => c.type === "text");
+			const textResult = textContent.map((c) => c.text).join("\n");
+			const imageContent = model.input.includes("image")
+				? msg.content.filter((c): c is ImageContent => c.type === "image")
+				: [];
 
 			// Always add functionResponse with text result (or placeholder if only images)
 			const hasText = textResult.length > 0;
-			const hasImages = imageBlocks.length > 0;
+			const hasImages = imageContent.length > 0;
+
+			// Use "output" key for success, "error" key for errors as per SDK documentation
+			const responseValue = hasText ? sanitizeSurrogates(textResult) : hasImages ? "(see attached image)" : "";
 
 			parts.push({
 				functionResponse: {
 					id: msg.toolCallId,
 					name: msg.toolName,
-					response: {
-						result: hasText ? sanitizeSurrogates(textResult) : hasImages ? "(see attached image)" : "",
-						isError: msg.isError,
-					},
+					response: msg.isError ? { error: responseValue } : { output: responseValue },
 				},
 			});
 
 			// Add any images as inlineData parts
-			for (const imageBlock of imageBlocks) {
+			for (const imageBlock of imageContent) {
 				parts.push({
 					inlineData: {
-						mimeType: (imageBlock as any).mimeType,
-						data: (imageBlock as any).data,
+						mimeType: imageBlock.mimeType,
+						data: imageBlock.data,
 					},
 				});
 			}
@@ -430,14 +437,16 @@ function convertMessages(model: Model<"google-generative-ai">, context: Context)
 	return contents;
 }
 
-function convertTools(tools: Tool[]): any[] | undefined {
+function convertTools(
+	tools: Tool[],
+): { functionDeclarations: { name: string; description?: string; parameters: Schema }[] }[] | undefined {
 	if (tools.length === 0) return undefined;
 	return [
 		{
 			functionDeclarations: tools.map((tool) => ({
 				name: tool.name,
 				description: tool.description,
-				parameters: tool.parameters as any, // TypeBox already generates JSON Schema
+				parameters: tool.parameters as Schema, // TypeBox generates JSON Schema compatible with SDK Schema type
 			})),
 		},
 	];