feat: Auto-detect transport type from config files

When launching the inspector with --config, automatically set the transport
dropdown and server URL based on the config file contents. This eliminates
the need to manually switch between stdio/sse/streamable-http in the UI.

- Use discriminated union for ServerConfig to properly type different transports
- Detect transport type and URL from config, pass via query params
- Maintain backwards compatibility for configs without explicit 'type' field
- Add comprehensive tests for the new functionality

Improves UX by making the config file the single source of truth for
server settings.

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

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

cli/src/cli.ts

@@ -14,6 +14,8 @@ type Args = {
   args: string[];
   envArgs: Record<string, string>;
   cli: boolean;
+  transport?: "stdio" | "sse" | "streamable-http";
+  serverUrl?: string;
 };
 
 type CliOptions = {
@@ -23,11 +25,18 @@ type CliOptions = {
   cli?: boolean;
 };
 
-type ServerConfig = {
-  command: string;
-  args?: string[];
-  env?: Record<string, string>;
-};
+type ServerConfig =
+  | {
+      type: "stdio";
+      command: string;
+      args?: string[];
+      env?: Record<string, string>;
+    }
+  | {
+      type: "sse" | "streamable-http";
+      url: string;
+      note?: string;
+    };
 
 function handleError(error: unknown): never {
   let message: string;
@@ -74,6 +83,16 @@ async function runWebClient(args: Args): Promise<void> {
     startArgs.push("-e", `${key}=${value}`);
   }
 
+  // Pass transport type if specified
+  if (args.transport) {
+    startArgs.push("--transport", args.transport);
+  }
+
+  // Pass server URL if specified
+  if (args.serverUrl) {
+    startArgs.push("--server-url", args.serverUrl);
+  }
+
   // Pass command and args (using -- to separate them)
   if (args.command) {
     startArgs.push("--", args.command, ...args.args);
@@ -217,12 +236,33 @@ function parseArgs(): Args {
   if (options.config && options.server) {
     const config = loadConfigFile(options.config, options.server);
 
-    return {
-      command: config.command,
-      args: [...(config.args || []), ...finalArgs],
-      envArgs: { ...(config.env || {}), ...(options.e || {}) },
-      cli: options.cli || false,
-    };
+    if (config.type === "stdio") {
+      return {
+        command: config.command,
+        args: [...(config.args || []), ...finalArgs],
+        envArgs: { ...(config.env || {}), ...(options.e || {}) },
+        cli: options.cli || false,
+        transport: "stdio",
+      };
+    } else if (config.type === "sse" || config.type === "streamable-http") {
+      return {
+        command: "",
+        args: finalArgs,
+        envArgs: options.e || {},
+        cli: options.cli || false,
+        transport: config.type,
+        serverUrl: config.url,
+      };
+    } else {
+      // Backwards compatibility: if no type field, assume stdio
+      return {
+        command: (config as any).command || "",
+        args: [...((config as any).args || []), ...finalArgs],
+        envArgs: { ...((config as any).env || {}), ...(options.e || {}) },
+        cli: options.cli || false,
+        transport: "stdio",
+      };
+    }
   }
 
   // Otherwise use command line arguments

client/bin/start.js

@@ -13,7 +13,14 @@ function delay(ms) {
   return new Promise((resolve) => setTimeout(resolve, ms, true));
 }
 
-function getClientUrl(port, authDisabled, sessionToken, serverPort) {
+function getClientUrl(
+  port,
+  authDisabled,
+  sessionToken,
+  serverPort,
+  transport,
+  serverUrl,
+) {
   const host = process.env.HOST || "localhost";
   const baseUrl = `http://${host}:${port}`;
 
@@ -24,6 +31,12 @@ function getClientUrl(port, authDisabled, sessionToken, serverPort) {
   if (!authDisabled) {
     params.set("MCP_PROXY_AUTH_TOKEN", sessionToken);
   }
+  if (transport) {
+    params.set("transport", transport);
+  }
+  if (serverUrl) {
+    params.set("serverUrl", serverUrl);
+  }
   return params.size > 0 ? `${baseUrl}/?${params.toString()}` : baseUrl;
 }
 
@@ -123,6 +136,8 @@ async function startDevClient(clientOptions) {
     sessionToken,
     abort,
     cancelled,
+    transport,
+    serverUrl,
   } = clientOptions;
   const clientCommand = "npx";
   const host = process.env.HOST || "localhost";
@@ -140,6 +155,8 @@ async function startDevClient(clientOptions) {
     authDisabled,
     sessionToken,
     SERVER_PORT,
+    transport,
+    serverUrl,
   );
 
   // Give vite time to start before opening or logging the URL
@@ -173,6 +190,8 @@ async function startProdClient(clientOptions) {
     sessionToken,
     abort,
     cancelled,
+    transport,
+    serverUrl,
   } = clientOptions;
   const inspectorClientPath = resolve(
     __dirname,
@@ -187,6 +206,8 @@ async function startProdClient(clientOptions) {
     authDisabled,
     sessionToken,
     SERVER_PORT,
+    transport,
+    serverUrl,
   );
 
   await spawnPromise("node", [inspectorClientPath], {
@@ -208,6 +229,8 @@ async function main() {
   let command = null;
   let parsingFlags = true;
   let isDev = false;
+  let transport = null;
+  let serverUrl = null;
 
   for (let i = 0; i < args.length; i++) {
     const arg = args[i];
@@ -233,6 +256,10 @@ async function main() {
       } else {
         envVars[envVar] = "";
       }
+    } else if (parsingFlags && arg === "--transport" && i + 1 < args.length) {
+      transport = args[++i];
+    } else if (parsingFlags && arg === "--server-url" && i + 1 < args.length) {
+      serverUrl = args[++i];
     } else if (!command && !isDev) {
       command = arg;
     } else if (!isDev) {
@@ -292,6 +319,8 @@ async function main() {
         sessionToken,
         abort,
         cancelled,
+        transport,
+        serverUrl,
       };
 
       await (isDev