Every page wraps itself in AppLayout, so a flashed redirect that lands on
a different page component tears the layout down and builds it again --
Toaster with it. The fresh Toaster then reads the flash at mount *and*
catches the router success event for the same visit, and every "Client
created." arrived twice. Saves that stay on the same component never
remount, which is why this survived unnoticed.
Deduping on the flash object's identity rather than its text is what
keeps the success listener doing its job: two genuine identical messages
in a row are separate objects and still both toast.
Verified in a real browser rather than by types: create a client, two
toasts before, one after, and two consecutive creates over SPA
navigation still toast once each.
Reported and diagnosed by @denkfabrik-li in #1675.
ignacionelson
4f38c9adee