fix: instant toggle exit via SIGUSR1 poll interruption

Remove SA_RESTART from the signal handler so SIGUSR1 interrupts the
blocking poll() call with EINTR. Handle EINTR gracefully in the event
loop to check should_exit() immediately instead of waiting for timeout.

src/lock.rs

@@ -73,9 +73,11 @@ pub fn create_lock() -> Result<LockGuard> {
     let path = lock_file_path();
 
     // Install SIGUSR1 handler before writing the lock file.
+    // No SA_RESTART — let the signal interrupt poll() so the event loop
+    // notices should_exit() promptly instead of waiting for the timeout.
     let action = SigAction::new(
         SigHandler::Handler(handle_sigusr1),
-        SaFlags::SA_RESTART,
+        SaFlags::empty(),
         SigSet::empty(),
     );
     unsafe { signal::sigaction(Signal::SIGUSR1, &action) }.context("install SIGUSR1 handler")?;

src/wayland.rs

@@ -163,7 +163,16 @@ impl WaylandBackend {
                     let mut pollfd =
                         [nix::poll::PollFd::new(fd, nix::poll::PollFlags::POLLIN)];
                     let millis = timeout.as_millis().min(u16::MAX as u128) as u16;
-                    let n = nix::poll::poll(&mut pollfd, millis).context("poll")?;
+                    let n = match nix::poll::poll(&mut pollfd, millis) {
+                        Ok(n) => n,
+                        Err(nix::errno::Errno::EINTR) => {
+                            // Signal interrupted poll — return so the loop
+                            // can check should_exit().
+                            drop(read_guard);
+                            return Ok(None);
+                        }
+                        Err(e) => return Err(e).context("poll"),
+                    };
 
                     if n > 0 {
                         let _ = read_guard.read();