ui: read structuredContent from MCP tool result when content is empty (#26691)

tools/ui/src/lib/services/mcp.service.ts

@@ -18,7 +18,8 @@ import {
 	DEFAULT_CLIENT_VERSION,
 	DEFAULT_IMAGE_MIME_TYPE,
 	DEFAULT_MCP_CONFIG,
-	HEADERS
+	HEADERS,
+	NEWLINE
 } from '$lib/constants';
 import {
 	MCPConnectionPhase,
@@ -70,6 +71,7 @@ interface ToolResultContentItem {
 
 interface ToolCallResult {
 	content?: ToolResultContentItem[];
+	structuredContent?: Record<string, unknown>;
 	isError?: boolean;
 	_meta?: Record<string, unknown>;
 }
@@ -1012,10 +1014,20 @@ export class MCPService {
 
 		if (!Array.isArray(content)) return '';
 
-		return content
+		const formatted = content
 			.map((item) => this.formatSingleContent(item))
 			.filter(Boolean)
-			.join('\n');
+			.join(NEWLINE);
+
+		if (formatted !== '') {
+			return formatted;
+		}
+
+		if (result.structuredContent && typeof result.structuredContent === 'object') {
+			return JSON.stringify(result.structuredContent);
+		}
+
+		return '';
 	}
 
 	private static formatSingleContent(content: ToolResultContentItem): string {