Fix tray icon not appearing after reboot on macOS

The tray icon would fail to appear when the app auto-started at login
because launchd was launching it before WindowServer was ready.

- Add LimitLoadToSessionType=Aqua to launchd plist to ensure the app
  only starts when a GUI session is available
- Add WaitForGUI() fallback that waits for WindowServer before
  initializing systray

Users with existing auto-start will need to run `nfc-agent uninstall`
then `nfc-agent install` to get the updated plist.

Author: AlbertMN

internal/service/service_darwin.go

@@ -24,6 +24,10 @@ const (
     </array>
     <key>RunAtLoad</key>
     <true/>
+    <key>LimitLoadToSessionType</key>
+    <string>Aqua</string>
+    <key>ProcessType</key>
+    <string>Interactive</string>
     <key>KeepAlive</key>
     <dict>
         <key>SuccessfulExit</key>

internal/tray/gui_darwin.go

@@ -0,0 +1,32 @@
+//go:build darwin
+
+package tray
+
+import (
+	"log"
+	"os/exec"
+	"time"
+)
+
+// WaitForGUI waits for the GUI/WindowServer to be ready.
+// Uses pgrep to check for WindowServer process.
+// Returns true if GUI is ready, false if timed out.
+func WaitForGUI(timeout time.Duration, retryInterval time.Duration) bool {
+	deadline := time.Now().Add(timeout)
+
+	for time.Now().Before(deadline) {
+		// Check if WindowServer process exists
+		cmd := exec.Command("pgrep", "-x", "WindowServer")
+		if err := cmd.Run(); err == nil {
+			// WindowServer is running, give it a moment to be fully ready
+			time.Sleep(500 * time.Millisecond)
+			log.Println("WindowServer is ready")
+			return true
+		}
+		log.Printf("Waiting for WindowServer... (%.0fs remaining)", time.Until(deadline).Seconds())
+		time.Sleep(retryInterval)
+	}
+
+	log.Println("Timed out waiting for WindowServer")
+	return false
+}

internal/tray/gui_other.go

@@ -0,0 +1,11 @@
+//go:build !darwin
+
+package tray
+
+import "time"
+
+// WaitForGUI is a no-op on non-macOS platforms.
+// Returns true immediately as no GUI wait is needed.
+func WaitForGUI(timeout time.Duration, retryInterval time.Duration) bool {
+	return true
+}

internal/tray/tray.go

@@ -8,6 +8,7 @@ import (
 	"os/exec"
 	"runtime"
 	"sync"
+	"time"
 
 	"github.com/SimplyPrint/nfc-agent/internal/api"
 	"github.com/SimplyPrint/nfc-agent/internal/core"
@@ -47,6 +48,11 @@ func (t *TrayApp) Run() {
 // RunWithServer runs the tray on the main thread and starts the server in a goroutine.
 // This function BLOCKS - it must be called from the main goroutine on macOS.
 func (t *TrayApp) RunWithServer(serverStart func()) {
+	// Wait for GUI/WindowServer to be ready (handles macOS startup race condition)
+	if !WaitForGUI(30*time.Second, 1*time.Second) {
+		log.Println("Warning: GUI may not be ready, systray initialization may fail")
+	}
+
 	systray.Run(func() {
 		t.onReady()
 		if serverStart != nil {