Announce a session's end when it is actually over, and for closes too

The phone's notification kept saying '1 shell connected' after the
shell was gone, and both close routes were at fault. A shell exiting on
its own raised SessionEnded from inside its run's finally block — where
the run task is by definition not yet complete, so the LiveSessionCount
the keep-alive reads still counted the dead shell, and nothing fired
later to correct it. A tab closed by hand announced nothing at all, by
a recorded decision that assumed every subscriber was the closer; the
keep-alive is not, and a close it never heard about left the
notification claiming a shell over nothing.

The end is now announced from a continuation after the run completes,
and CloseSessionAsync announces after its own drain — every subscriber
was already a reconcile-to-reality handler, so the echo the old remark
feared costs nothing. Shutdown stays silent: it is dismantling the
subscribers along with the sessions.

docs/android-port.md

@@ -348,6 +348,16 @@ runtime or the receipt is silently invisible — the service still runs, but not
 to show, at most once, with no result read back: a refusal costs the notification and nothing else, which is
 what the manifest's own comment on the permission says.
 
+**And a fourth correction, found by the notification refusing to come down.** "1 shell connected" outlived
+the shell, both ways a shell can close. A shell exiting on its own announced `SessionEnded` from inside its
+run's own finally block — where the run task is by definition not yet complete, so the
+`LiveSessionCount` the keep-alive reads from that event still counted the session that had just ended, and
+nothing fired afterwards to correct it. A tab closed by hand announced nothing at all, by a recorded
+decision that assumed every subscriber was the closer. Both reversed in `TerminalWorkspace`: the end is now
+announced from a continuation after the run has actually completed, and `CloseSessionAsync` announces too,
+after its own drain — the event's remark carries the reversal, and `SessionEnded`'s subscribers were all
+already "reconcile to reality" handlers for which a second announcement is harmless.
+
 ### Phone first
 
 About 360dp wide. The tablet route was cheaper — a landscape tablet is close to the existing 880×560 minimum