feat: enhance command classification and error handling; improve process checks and credential security

src/app/mcp/manager.rs

@@ -139,7 +139,9 @@ pub(crate) fn spawn_stdio_child(command: &str, extra_args: &[String]) -> anyhow:
     cmd.args(extra_args);
     cmd.stdin(std::process::Stdio::piped());
     cmd.stdout(std::process::Stdio::piped());
-    cmd.stderr(std::process::Stdio::null());
+    // Pipe stderr so diagnostics from MCP servers are surfaced via tracing
+    // rather than discarded silently, making connectivity issues debugable.
+    cmd.stderr(std::process::Stdio::piped());
 
     let mut child = cmd.spawn()
         .map_err(|e| anyhow::anyhow!("failed to spawn MCP stdio server '{}': {}", command, e))?;