Invite links: starsync:// opens the app and asks to join; one app per profile; real invite address; clipboard pick-up

- starsync://host:port/?name=&pw= (PROTOCOL.md "Invite link"); the password only when ticked, never in logs
- Linux: launcher entry takes x-scheme-handler/starsync (%u, StartupNotify) and becomes its xdg-mime default; Windows: HKCU\Software\Classes\starsync -> starsync.exe
- InstanceLock: lock file + loopback handoff per profile folder; the running app comes up with the second start's activation token (Wayland/X11) or AllowSetForegroundWindow (Windows)
- Sharing looks up the internet address (HTTPS services with fallbacks); members card picks Internet / Home network / VPN and says when the port needs forwarding
- JoinOffers: link and clipboard prompt with /health, joins through ConnectFlow; dismissed clipboard invites kept as fingerprints

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

apps/desktop/windows/runner/flutter_window.cpp

@@ -52,6 +52,13 @@ bool FlutterWindow::OnCreate() {
   window_channel_->SetMethodCallHandler(
       [this](const flutter::MethodCall<flutter::EncodableValue>& call,
              std::unique_ptr<flutter::MethodResult<flutter::EncodableValue>> result) {
+        // A second start that handed its link to the running app ends
+        // here, before its window ever shows (no CRT exit, no DLL detach).
+        if (call.method_name() == "exit") {
+          fflush(nullptr);
+          ::TerminateProcess(::GetCurrentProcess(), 0);
+          return;
+        }
         if (call.method_name() != "attention") {
           result->NotImplemented();
           return;