Add image support in tool results across all providers

Tool results now use content blocks and can include both text and images.
All providers (Anthropic, Google, OpenAI Completions, OpenAI Responses)
correctly pass images from tool results to LLMs.

- Update ToolResultMessage type to use content blocks
- Add placeholder text for image-only tool results in Google/Anthropic
- OpenAI providers send tool result + follow-up user message with images
- Fix Anthropic JSON parsing for empty tool arguments
- Add comprehensive tests for image-only and text+image tool results
- Update README with tool result content blocks API

packages/ai/src/agent/agent-loop.ts

@@ -216,11 +216,15 @@ async function executeToolCalls<T>(
 			isError,
 		});
 
+		// Convert result to content blocks
+		const content: ToolResultMessage<T>["content"] =
+			typeof resultOrError === "string" ? [{ type: "text", text: resultOrError }] : resultOrError.content;
+
 		const toolResultMessage: ToolResultMessage<T> = {
 			role: "toolResult",
 			toolCallId: toolCall.id,
 			toolName: toolCall.name,
-			output: typeof resultOrError === "string" ? resultOrError : resultOrError.output,
+			content,
 			details: typeof resultOrError === "string" ? ({} as T) : resultOrError.details,
 			isError,
 			timestamp: Date.now(),

packages/ai/src/agent/tools/calculate.ts

@@ -1,15 +1,15 @@
 import { type Static, Type } from "@sinclair/typebox";
-import type { AgentTool } from "../../agent/types.js";
+import type { AgentTool, AgentToolResult } from "../../agent/types.js";
 
-export interface CalculateResult {
-	output: string;
+export interface CalculateResult extends AgentToolResult<undefined> {
+	content: Array<{ type: "text"; text: string }>;
 	details: undefined;
 }
 
 export function calculate(expression: string): CalculateResult {
 	try {
 		const result = new Function("return " + expression)();
-		return { output: `${expression} = ${result}`, details: undefined };
+		return { content: [{ type: "text", text: `${expression} = ${result}` }], details: undefined };
 	} catch (e: any) {
 		throw new Error(e.message || String(e));
 	}

packages/ai/src/agent/tools/get-current-time.ts

@@ -8,20 +8,22 @@ export async function getCurrentTime(timezone?: string): Promise<GetCurrentTimeR
 	const date = new Date();
 	if (timezone) {
 		try {
+			const timeStr = date.toLocaleString("en-US", {
+				timeZone: timezone,
+				dateStyle: "full",
+				timeStyle: "long",
+			});
 			return {
-				output: date.toLocaleString("en-US", {
-					timeZone: timezone,
-					dateStyle: "full",
-					timeStyle: "long",
-				}),
+				content: [{ type: "text", text: timeStr }],
 				details: { utcTimestamp: date.getTime() },
 			};
 		} catch (e) {
 			throw new Error(`Invalid timezone: ${timezone}. Current UTC time: ${date.toISOString()}`);
 		}
 	}
+	const timeStr = date.toLocaleString("en-US", { dateStyle: "full", timeStyle: "long" });
 	return {
-		output: date.toLocaleString("en-US", { dateStyle: "full", timeStyle: "long" }),
+		content: [{ type: "text", text: timeStr }],
 		details: { utcTimestamp: date.getTime() },
 	};
 }

packages/ai/src/agent/types.ts

@@ -2,17 +2,19 @@ import type { Static, TSchema } from "@sinclair/typebox";
 import type {
 	AssistantMessage,
 	AssistantMessageEvent,
+	ImageContent,
 	Message,
 	Model,
 	SimpleStreamOptions,
+	TextContent,
 	Tool,
 	ToolResultMessage,
 } from "../types.js";
 
 export interface AgentToolResult<T> {
-	// Output of the tool to be given to the LLM in ToolResultMessage.content
-	output: string;
-	// Details to be displayed in a UI or loggedty
+	// Content blocks supporting text and images
+	content: (TextContent | ImageContent)[];
+	// Details to be displayed in a UI or logged
 	details: T;
 }