fix: use blob field for binary resources to prevent context overflow (cloudflare#252)

Binary content (images, etc.) was incorrectly using 'text' field, causing MCP hosts like Claude Desktop to display base64 strings as text messages, flooding the context window.

Changed to use 'blob' field for binary data per MCP 2025-06-18 spec.

Author: MurphyLo

apps/sandbox-container/server/containerMcp.ts

@@ -165,7 +165,10 @@ export class ContainerMcpAgent extends McpAgent<Env, never, Props> {
 						{
 							type: 'resource',
 							resource: {
-								text: readFile.type === 'text' ? readFile.textOutput : readFile.base64Output,
+								...(readFile.type === 'text' 
+									? { text: readFile.textOutput }
+									: { blob: readFile.base64Output }
+								),
 								uri: `file://${path}`,
 								mimeType: readFile.mimeType,
 							},