`onWindowStateChanged` merged the fullscreen / traffic-light payload into
`$connection`, but only when a connection was already published; while
`$connection` was null (mid-boot, or between a dropped primary and its
fallback resolving) the payload was dropped. Main snapshots the chrome
state into each descriptor at mint time, so a toggle that fires after the
mint but before the renderer publishes it is newer than the snapshot and
never reached the titlebar cluster until the next toggle — the third
root-cause atom of #108641.
Buffer the last payload while nothing is published and fold it into the
next non-null publish, then clear it: later descriptors carry their own
fresh snapshot.
a02e1d78a4