pub fn spawn(startup_rx: Receiver<StartupEvent>)Expand description
Spawn the startup splash. Sets AGENTMUX_SPLASH_READY_FILE (inherited by the
host, which writes it on first paint) and runs the matching backend on a
dedicated thread, so the launcher’s main thread continues to start srv + host.
The thread self-terminates on first-paint or the safety timeout. Best-effort:
any failure (no display, protocol error) just means no splash — the launcher
is unaffected.
startup_rx is the receiver end of the startup event bus. The splash thread
drains it every animation frame to update the stage list. Pass the receiver
from startup_events::StartupEventSink::new() created in main() before
the Tokio runtime is started.