fix(startup): make watchdog task keep agent alive

- Use Task Scheduler XML instead of /TR
- Run -ensure agent in-process, not child
- Add console close and panic protection
- Guard nil event channels after stop
- Add non-Windows stubs for startup/mutex

lib/instance/console_windows.go

@@ -8,17 +8,27 @@ import (
 )
 
 var (
-	kernel32        = syscall.NewLazyDLL("kernel32.dll")
-	procFreeConsole = kernel32.NewProc("FreeConsole")
-	user32          = syscall.NewLazyDLL("user32.dll")
-	procShowWindow  = user32.NewProc("ShowWindow")
+	kernel32             = syscall.NewLazyDLL("kernel32.dll")
+	procFreeConsole      = kernel32.NewProc("FreeConsole")
+	procGetConsoleWindow = kernel32.NewProc("GetConsoleWindow")
+	procSetConsoleCtrl   = kernel32.NewProc("SetConsoleCtrlHandler")
+	procAllocConsole     = kernel32.NewProc("AllocConsole")
+	procGetStdHandle     = kernel32.NewProc("GetStdHandle")
+	user32               = syscall.NewLazyDLL("user32.dll")
+	procShowWindow       = user32.NewProc("ShowWindow")
+	consoleCtrlCallback  uintptr
 )
 
-const swHide = 0
+const (
+	swHide         = 0
+	ctrlCEvent     = 0
+	ctrlBreakEvent = 1
+	ctrlCloseEvent = 2
+)
 
 // HideConsole hides any console window and detaches from it.
 func HideConsole() {
-	hwnd, _, _ := kernel32.NewProc("GetConsoleWindow").Call()
+	hwnd, _, _ := procGetConsoleWindow.Call()
 	if hwnd != 0 {
 		_, _, _ = procShowWindow.Call(hwnd, swHide)
 	}
@@ -26,6 +36,35 @@ func HideConsole() {
 	redirectStdioToNul()
 }
 
+// ShowConsole allocates a console for -foreground when built as a GUI binary.
+func ShowConsole() {
+	_, _, _ = procAllocConsole.Call()
+	hin, _, _ := procGetStdHandle.Call(^uintptr(9))   // STD_INPUT_HANDLE
+	hout, _, _ := procGetStdHandle.Call(^uintptr(10)) // STD_OUTPUT_HANDLE
+	herr, _, _ := procGetStdHandle.Call(^uintptr(11)) // STD_ERROR_HANDLE
+	os.Stdin = os.NewFile(hin, "stdin")
+	os.Stdout = os.NewFile(hout, "stdout")
+	os.Stderr = os.NewFile(herr, "stderr")
+}
+
+// ProtectFromConsoleClose ignores Ctrl+C/Break/close so Task Scheduler and
+// explorer do not kill the process when the flashed console goes away.
+func ProtectFromConsoleClose() {
+	if consoleCtrlCallback == 0 {
+		consoleCtrlCallback = syscall.NewCallback(consoleCtrlHandler)
+	}
+	_, _, _ = procSetConsoleCtrl.Call(consoleCtrlCallback, 1)
+}
+
+func consoleCtrlHandler(ctrlType uintptr) uintptr {
+	switch uint32(ctrlType) {
+	case ctrlCEvent, ctrlBreakEvent, ctrlCloseEvent:
+		return 1
+	default:
+		return 0
+	}
+}
+
 func redirectStdioToNul() {
 	nul, err := os.OpenFile("NUL", os.O_RDWR, 0)
 	if err != nil {