mcp: make discovery good

- There's an mcpDiscoveryRegistry that allows components to register in
  how they discover MCP servers.
- Config discovery is one of these. Figured out all the bits for a
  standalone file config shebang. Duplication there that could be
  cleaned up but it works.
- The others are remote and local filesystem discovery. I ended up
  making another message channel for the main process/remote server to
  get a couple environment variables we need since I didn't see anything
  generic for this already(?)

![](https://memes.peet.io/img/25-03-29927218-daa9-4206-8cef-29992850d9ba.mp4)

src/vs/code/electron-main/app.ts

@@ -118,6 +118,8 @@ import { IAuxiliaryWindowsMainService } from '../../platform/auxiliaryWindow/ele
 import { AuxiliaryWindowsMainService } from '../../platform/auxiliaryWindow/electron-main/auxiliaryWindowsMainService.js';
 import { normalizeNFC } from '../../base/common/normalization.js';
 import { ICSSDevelopmentService, CSSDevelopmentService } from '../../platform/cssDev/node/cssDevService.js';
+import { NativeMcpDiscoveryHelperChannelName } from '../../platform/mcp/common/nativeMcpDiscoveryHelper.js';
+import { NativeMcpDiscoveryHelperChannel } from '../../platform/mcp/node/nativeMcpDiscoveryHelperChannel.js';
 
 /**
  * The main VS Code application. There will only ever be one instance,
@@ -1222,6 +1224,9 @@ export class CodeApplication extends Disposable {
 		const externalTerminalChannel = ProxyChannel.fromService(accessor.get(IExternalTerminalMainService), disposables);
 		mainProcessElectronServer.registerChannel('externalTerminal', externalTerminalChannel);
 
+		// MCP
+		mainProcessElectronServer.registerChannel(NativeMcpDiscoveryHelperChannelName, new NativeMcpDiscoveryHelperChannel(undefined));
+
 		// Logger
 		const loggerChannel = new LoggerChannel(accessor.get(ILoggerMainService),);
 		mainProcessElectronServer.registerChannel('logger', loggerChannel);