Forward what the budget and visibility now allow.
Drop every queue and counter for a window.
Admit, hold or drop one window-level message. Messages from unregistered windows are forwarded so the bridge can report them as unrouted.
Judge one envelope that arrived over a bound port. kehto calls this
synchronously just before it dispatches the envelope to the runtime, so
nothing can be held or delayed here; the caller refuses instead. A
defer or reject answer means the envelope must not be handled:
createKernl refuses it for that one dispatch with
refuseCurrentDispatch. That covers bursts above the per-second rate,
the focus-aware firewall, size caps, and every non-control envelope from
a window that is not visible (reason hidden:<class>), which the applet
can retry once it is visible. Control envelopes are never refused. A
quarantine triggers onQuarantine, and when that revokes the binding
kehto no longer finds the window's session and drops the envelope.
Lift quarantine after the user chose to.
Rebuild every layer for a profile. Held messages are dropped; counters restart.
The composed guard the shell puts in front of kehto's bridge.