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/README.md

@@ -98,7 +98,6 @@ for await (const event of s) {
 const finalMessage = await s.result();
 context.messages.push(finalMessage);
 
-// Handle tool calls if any
 // Handle tool calls if any
 const toolCalls = finalMessage.content.filter(b => b.type === 'toolCall');
 for (const call of toolCalls) {
@@ -111,13 +110,14 @@ for (const call of toolCalls) {
       })
     : 'Unknown tool';
 
-  // Add tool result to context
+  // Add tool result to context (supports text and images)
   context.messages.push({
     role: 'toolResult',
     toolCallId: call.id,
     toolName: call.name,
-    output: result,
-    isError: false
+    content: [{ type: 'text', text: result }],
+    isError: false,
+    timestamp: Date.now()
   });
 }
 
@@ -179,7 +179,11 @@ const bookMeetingTool: Tool = {
 
 ### Handling Tool Calls
 
+Tool results use content blocks and can include both text and images:
+
 ```typescript
+import { readFileSync } from 'fs';
+
 const context: Context = {
   messages: [{ role: 'user', content: 'What is the weather in London?' }],
   tools: [weatherTool]
@@ -194,16 +198,31 @@ for (const block of response.content) {
     // If validation fails, an error event is emitted
     const result = await executeWeatherApi(block.arguments);
 
-    // Add tool result to continue the conversation
+    // Add tool result with text content
     context.messages.push({
       role: 'toolResult',
       toolCallId: block.id,
       toolName: block.name,
-      output: JSON.stringify(result),
-      isError: false
+      content: [{ type: 'text', text: JSON.stringify(result) }],
+      isError: false,
+      timestamp: Date.now()
     });
   }
 }
+
+// Tool results can also include images (for vision-capable models)
+const imageBuffer = readFileSync('chart.png');
+context.messages.push({
+  role: 'toolResult',
+  toolCallId: 'tool_xyz',
+  toolName: 'generate_chart',
+  content: [
+    { type: 'text', text: 'Generated chart showing temperature trends' },
+    { type: 'image', data: imageBuffer.toString('base64'), mimeType: 'image/png' }
+  ],
+  isError: false,
+  timestamp: Date.now()
+});
 ```
 
 ### Streaming Tool Calls with Partial JSON
@@ -625,7 +644,7 @@ const geminiResponse = await complete(gemini, context);
 
 All providers can handle messages from other providers, including:
 - Text content
-- Tool calls and tool results
+- Tool calls and tool results (including images in tool results)
 - Thinking/reasoning blocks (transformed to tagged text for cross-provider compatibility)
 - Aborted messages with partial content
 
@@ -818,6 +837,23 @@ const weatherTool: AgentTool<typeof weatherSchema, { temp: number }> = {
     };
   }
 };
+
+// Tools can also return images alongside text
+const chartTool: AgentTool<typeof Type.Object({ data: Type.Array(Type.Number()) })> = {
+  label: 'Generate Chart',
+  name: 'generate_chart',
+  description: 'Generate a chart from data',
+  parameters: Type.Object({ data: Type.Array(Type.Number()) }),
+  execute: async (toolCallId, args) => {
+    const chartImage = await generateChartImage(args.data);
+    return {
+      content: [
+        { type: 'text', text: `Generated chart with ${args.data.length} data points` },
+        { type: 'image', data: chartImage.toString('base64'), mimeType: 'image/png' }
+      ]
+    };
+  }
+};
 ```
 
 ### Validation and Error Handling