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/providers/anthropic.ts

@@ -9,6 +9,7 @@ import type {
 	Api,
 	AssistantMessage,
 	Context,
+	ImageContent,
 	Message,
 	Model,
 	StopReason,
@@ -26,6 +27,58 @@ import { sanitizeSurrogates } from "../utils/sanitize-unicode.js";
 import { validateToolArguments } from "../utils/validation.js";
 import { transformMessages } from "./transorm-messages.js";
 
+/**
+ * Convert content blocks to Anthropic API format
+ */
+function convertContentBlocks(content: (TextContent | ImageContent)[]):
+	| string
+	| Array<
+			| { type: "text"; text: string }
+			| {
+					type: "image";
+					source: {
+						type: "base64";
+						media_type: "image/jpeg" | "image/png" | "image/gif" | "image/webp";
+						data: string;
+					};
+			  }
+	  > {
+	// If only text blocks, return as concatenated string for simplicity
+	const hasImages = content.some((c) => c.type === "image");
+	if (!hasImages) {
+		return sanitizeSurrogates(content.map((c) => (c as TextContent).text).join("\n"));
+	}
+
+	// If we have images, convert to content block array
+	const blocks = content.map((block) => {
+		if (block.type === "text") {
+			return {
+				type: "text" as const,
+				text: sanitizeSurrogates(block.text),
+			};
+		}
+		return {
+			type: "image" as const,
+			source: {
+				type: "base64" as const,
+				media_type: block.mimeType as "image/jpeg" | "image/png" | "image/gif" | "image/webp",
+				data: block.data,
+			},
+		};
+	});
+
+	// If only images (no text), add placeholder text block
+	const hasText = blocks.some((b) => b.type === "text");
+	if (!hasText) {
+		blocks.unshift({
+			type: "text" as const,
+			text: "(see attached image)",
+		});
+	}
+
+	return blocks;
+}
+
 export interface AnthropicOptions extends StreamOptions {
 	thinkingEnabled?: boolean;
 	thinkingBudgetTokens?: number;
@@ -171,7 +224,7 @@ export const streamAnthropic: StreamFunction<"anthropic-messages"> = (
 								partial: output,
 							});
 						} else if (block.type === "toolCall") {
-							block.arguments = JSON.parse(block.partialJson);
+							block.arguments = parseStreamingJson(block.partialJson);
 
 							// Validate tool arguments if tool definition is available
 							if (context.tools) {
@@ -432,7 +485,7 @@ function convertMessages(messages: Message[], model: Model<"anthropic-messages">
 			toolResults.push({
 				type: "tool_result",
 				tool_use_id: sanitizeToolCallId(msg.toolCallId),
-				content: sanitizeSurrogates(msg.output),
+				content: convertContentBlocks(msg.content),
 				is_error: msg.isError,
 			});
 
@@ -443,7 +496,7 @@ function convertMessages(messages: Message[], model: Model<"anthropic-messages">
 				toolResults.push({
 					type: "tool_result",
 					tool_use_id: sanitizeToolCallId(nextMsg.toolCallId),
-					content: sanitizeSurrogates(nextMsg.output),
+					content: convertContentBlocks(nextMsg.content),
 					is_error: nextMsg.isError,
 				});
 				j++;