The Capture request arm of Worker::process pre-parsed every window
target as a u64 before consulting the backend, so composite AT-SPI ids
minted by the Wayland backend's own windows() (e.g.
atspi::1.31:/org/a11y/atspi/accessible/1) could never pass the gate,
making per-window capture unreachable on Wayland in every build.
All backends resolve capture targets by string-matching against the ids
they themselves minted, so the u64 gate was a leaked X11/Win32/macOS
assumption. Drop it and let the backend validate the id; unknown ids now
fail as WindowNotFound from the backend lookup instead of InvalidTarget.
Fixes#7701
roboomp
2ef15378f6