Add error reporting for SITL child process failures

Previously, SITL spawn errors and unexpected exits were completely
silent - the renderer never subscribed to child process error/exit
events. Now errors are logged to both console and the GUI log so
users can see why Demo mode or SITL connections fail.

Also removes the ineffective useShell option (not a valid Node.js
spawn property, was silently ignored).

Author: sensei-hacker

js/main/child_process.js

@@ -3,17 +3,20 @@ import { spawn } from 'node:child_process'
 const child_process = {
     _processes: [],
 
-    start: function (command, args, opts, window) {        
+    start: function (command, args, opts, window) {
         var process;
         try {
             process = spawn(command, args, opts);
         } catch (err) {
-            console.log(err);
+            console.log(`[child_process] Spawn error: ${err.message}`);
+            if (!window.isDestroyed()) {
+                window.webContents.send('onChildProcessError', { message: `Spawn error: ${err.message}` });
+            }
             return -1;
         }
-        
+
         this._processes.push(process);
-        
+
         process.stdout.on('data', (data) => {
             if (!window.isDestroyed()) {
                 window.webContents.send('onChildProcessStdout', data.toString());
@@ -27,8 +30,15 @@ const child_process = {
         });
 
         process.on('error', (error) => {
+            console.log(`[child_process] Error: ${error.message}`);
+            if (!window.isDestroyed()) {
+                window.webContents.send('onChildProcessError', { message: error.message });
+            }
+        });
+
+        process.on('exit', (code, signal) => {
             if (!window.isDestroyed()) {
-                window.webContents.send('onChildProcessError', error);
+                window.webContents.send('onChildProcessExit', { code, signal });
             }
         });
     },

js/main/preload.js

@@ -95,4 +95,10 @@ contextBridge.exposeInMainWorld('electronAPI', {
     return handler;
   },
   offChildProcessError: (handler) => ipcRenderer.removeListener('onChildProcessError', handler),
+  onChildProcessExit: (callback) => {
+    const handler = (_event, data) => callback(data);
+    ipcRenderer.on('onChildProcessExit', handler);
+    return handler;
+  },
+  offChildProcessExit: (handler) => ipcRenderer.removeListener('onChildProcessExit', handler),
 });

js/sitl.js

@@ -183,17 +183,19 @@ var SITLProcess = {
 
     spawn: function(path, args) {
 
-        var opts = undefined;
-        if (GUI.operating_system == 'Linux')
-            opts = { useShell: true };
-
-        window.electronAPI.startChildProcess(path, args, opts);
-
-        if (this.processHandle == -1) {
+        window.electronAPI.onChildProcessError((error) => {
+            console.log(`SITL error: ${error.message || JSON.stringify(error)}`);
+            GUI.log(`SITL error: ${error.message || JSON.stringify(error)}`);
+        });
+        window.electronAPI.onChildProcessExit((data) => {
+            if (data.code !== 0 && data.code !== null) {
+                console.log(`SITL process exited with code ${data.code}`);
+                GUI.log(`SITL process exited with code ${data.code}`);
+            }
             this.isRunning = false;
-            return;
-        }
+        });
 
+        window.electronAPI.startChildProcess(path, args);
         this.isRunning = true;
     },