Toasts through WinRT, under the app id io.narl.proton-stream. The id is
registered for the current user under HKCU\Software\Classes\AppUserModelId
with a display name and icon on the first notification of a session, which
is what lets an app with no package or installer-made shortcut show one. If
that write fails, the toast goes out under PowerShell's id rather than not
at all.
A second launch hands its request to the open window and exits: over a
Unix socket in the user's runtime directory, or a named pipe on Windows
whose name carries a random key from the user's config directory, so
another account cannot take the name first. The open window comes forward,
and a share link given as the first such argument opens the Add form with
it filled in. Setup failures are logged and the app runs without the lock.
nvrl