usbscsid: replace .unwrap() in runtime with explicit error handling

Two runtime .unwrap() calls in the event loop are replaced with
explicit error logging and process::exit(1):
1. event::EventQueue::new() — fail to create event queue
2. event_queue.subscribe() — fail to subscribe to scheme events

Previously these panicked the daemon if the event subsystem
was unavailable. Now they log a clear error and exit gracefully.

Resolves IMPROVEMENT-PLAN §3.6: 'usbscsid: Fix .expect() in runtime'.

drivers/storage/usbscsid/src/main.rs

@@ -2,6 +2,7 @@ use std::collections::BTreeMap;
 use std::env;
 
 use driver_block::{Disk, DiskScheme, ExecutorTrait};
+use log::error;
 use syscall::{Error, EIO};
 use xhcid_interface::{ConfigureEndpointsReq, PortId, XhciClientHandle};
 
@@ -107,7 +108,13 @@ fn daemon(daemon: daemon::Daemon) -> ! {
         println!("DISK CONTENT: {}", base64::encode(&buffer[..]));
     }
 
-    let event_queue = event::EventQueue::new().unwrap();
+    let event_queue = match event::EventQueue::new() {
+        Ok(q) => q,
+        Err(e) => {
+            error!("usbscsid: failed to create event queue: {e}");
+            std::process::exit(1);
+        }
+    };
 
     event::user_data! {
         enum Event {
@@ -133,13 +140,14 @@ fn daemon(daemon: daemon::Daemon) -> ! {
 
     //libredox::call::setrens(0, 0).expect("nvmed: failed to enter null namespace");
 
-    event_queue
-        .subscribe(
-            scheme.event_handle().raw(),
-            Event::Scheme,
-            event::EventFlags::READ,
-        )
-        .unwrap();
+    if let Err(e) = event_queue.subscribe(
+        scheme.event_handle().raw(),
+        Event::Scheme,
+        event::EventFlags::READ,
+    ) {
+        error!("usbscsid: failed to subscribe to events: {e}");
+        std::process::exit(1);
+    }
 
     for event in event_queue {
         let event = match event {