Merge nucleic/sleek-thistle-egret-fyej into dev

brush-shell/src/entry.rs

@@ -193,9 +193,26 @@ pub fn run() {
         }
     };
 
+    run_exit_hook();
     std::process::exit(i32::from(exit_code));
 }
 
+// nash: a hook invoked right before the process exits, so an embedding shell
+// (nash) can flush its observation event buffer (docs/NASH.md §6.1).
+static EXIT_HOOK: std::sync::OnceLock<Box<dyn Fn() + Send + Sync>> = std::sync::OnceLock::new();
+
+/// nash: registers a hook run immediately before the shell process exits.
+/// May be called at most once; later calls are ignored.
+pub fn set_exit_hook(hook: Box<dyn Fn() + Send + Sync>) {
+    let _ = EXIT_HOOK.set(hook);
+}
+
+fn run_exit_hook() {
+    if let Some(hook) = EXIT_HOOK.get() {
+        hook();
+    }
+}
+
 /// Installs panic handlers to report our panic and cleanly exit on panic.
 fn install_panic_handlers() {
     //