Add support for outputSchema and optional content fields in tools

- Add outputSchema field to Tool type and RegisteredTool interface
- Make content field optional in CallToolResult
- Update ListToolsRequestSchema handler to include outputSchema in tool list responses
- Add support for structuredContent in tool results
- Update examples to handle optional content field
- Add tests for new outputSchema and structuredContent functionality
- Update ToolCallback documentation to clarify when to use structuredContent vs content

This change enables tools to define structured output schemas and return
structured JSON content, providing better type safety and validation for
tool outputs.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

src/examples/client/parallelToolCallsClient.ts

@@ -61,13 +61,19 @@ async function main(): Promise<void> {
     // Log the results from each tool call
     for (const [caller, result] of Object.entries(toolResults)) {
       console.log(`\n=== Tool result for ${caller} ===`);
-      result.content.forEach((item: { type: string; text?: string; }) => {
-        if (item.type === 'text') {
-          console.log(`  ${item.text}`);
-        } else {
-          console.log(`  ${item.type} content:`, item);
-        }
-      });
+      if (result.content) {
+        result.content.forEach((item: { type: string; text?: string; }) => {
+          if (item.type === 'text') {
+            console.log(`  ${item.text}`);
+          } else {
+            console.log(`  ${item.type} content:`, item);
+          }
+        });
+      } else if (result.structuredContent) {
+        console.log(`  Structured content: ${result.structuredContent}`);
+      } else {
+        console.log(`  No content returned`);
+      }
     }
 
     // 3. Wait for all notifications (10 seconds)

src/examples/client/simpleStreamableHttp.ts

@@ -341,13 +341,19 @@ async function callTool(name: string, args: Record<string, unknown>): Promise<vo
     });
 
     console.log('Tool result:');
-    result.content.forEach(item => {
-      if (item.type === 'text') {
-        console.log(`  ${item.text}`);
-      } else {
-        console.log(`  ${item.type} content:`, item);
-      }
-    });
+    if (result.content) {
+      result.content.forEach(item => {
+        if (item.type === 'text') {
+          console.log(`  ${item.text}`);
+        } else {
+          console.log(`  ${item.type} content:`, item);
+        }
+      });
+    } else if (result.structuredContent) {
+      console.log(`  Structured content: ${result.structuredContent}`);
+    } else {
+      console.log('  No content returned');
+    }
   } catch (error) {
     console.log(`Error calling tool ${name}: ${error}`);
   }

src/examples/client/streamableHttpWithSseFallbackClient.ts

@@ -173,13 +173,19 @@ async function startNotificationTool(client: Client): Promise<void> {
     const result = await client.request(request, CallToolResultSchema);
 
     console.log('Tool result:');
-    result.content.forEach(item => {
-      if (item.type === 'text') {
-        console.log(`  ${item.text}`);
-      } else {
-        console.log(`  ${item.type} content:`, item);
-      }
-    });
+    if (result.content) {
+      result.content.forEach(item => {
+        if (item.type === 'text') {
+          console.log(`  ${item.text}`);
+        } else {
+          console.log(`  ${item.type} content:`, item);
+        }
+      });
+    } else if (result.structuredContent) {
+      console.log(`  Structured content: ${result.structuredContent}`);
+    } else {
+      console.log('  No content returned');
+    }
   } catch (error) {
     console.log(`Error calling notification tool: ${error}`);
   }