Slack posts are durable workspace messages, not an ephemeral terminal
status area. Default long_running_notifications and busy_ack_detail to
off for Slack so long-running agent work does not leave permanent
operational breadcrumbs like 'Working — 9 min — iteration 12/90' in
channels. Both remain opt-in per platform via
display.platforms.slack.*.
Also covers the platform-generic shutdown-notification mute path with a
regression test (gateway_restart_notification=false must suppress both
the active-session interruption notice and the home-channel copy).
Salvaged from #69028 (quiet-defaults half only). The PR's other half —
the channel_session_scope_channels session-scoping feature — is a new
config feature outside this log-noise cluster and overlaps the session
scoping territory reworked by merged wave-1/2 Slack session work; it is
deliberately not taken here.
wpeterr
390ddfd028