Function install_close_on_exit_handler 

pub fn install_close_on_exit_handler(state: &AppState)

Wires blockcontroller::close_on_exit (see that function’s own doc comment) up to the real close action, now that AppState exists. Mirrors install_agent_turn_delivery just above — same “backend code needs a capability only available once AppState is built” shape, solved the same way (a process-wide callback set once at boot).

The callback itself is deliberately synchronous (Fn(String, String), not async fn) — shell/lifecycle.rs’s wait/cleanup task calls it from a plain (non-async) decision point after its own cleanup, and trait objects can’t hold an async fn without extra boxing machinery this doesn’t need. tokio::spawn here is what actually runs the (necessarily async) sagas::delete_block::run call; the callback returns immediately, fire-and-forget, matching close_on_exit’s own contract.

See docs/specs/SPEC_TERM_EXIT_RESPAWN_LOOP_2026_09_15.md §10 for why this exists: a shell pane’s controller has no code path today that closes it when the shell process exits, which (combined with §7-9’s fix for the OTHER half of that bug) leaves an exited pane sitting inert — technically correct, but indistinguishable from “hung” to a user.