The fire-and-forget run captured its session's pi/ctx; after /new, fork,
switch, or reload pi invalidates those, so the orphaned run's notify/
sendMessage threw 'This extension ctx is stale after session replacement
or reload'. Now session_shutdown aborts the in-flight run before
invalidation (pi.exec supports AbortSignal), and stale errors are
swallowed as a race guard.
Also show a 'running tests...' footer status widget while the run is
in flight, cleared on completion.
Emit test-balls:record on the shared pi.events bus after the session-start
make test run completes, so test-balls shows a ball for it like any other run.
The run is now fire-and-forget: session start no longer blocks on make test,
and the emit always lands after every extension's session_start handler has
run (project extensions load before global ones, so emitting synchronously
raced test-balls' runs reset). Exactly one ball is recorded per run, even if
UI reporting fails.