fix: use ctrlc crate for cross-platform Ctrl+C detection in pty test

Replace platform-divergent signal-hook (Unix) / default-handler (Windows)
approach with the `ctrlc` crate on both platforms. The handler writes
"INTERRUPTED" and exits directly, avoiding race conditions between the
callback thread and main thread.

On Windows, the Rust runtime sets SetConsoleCtrlHandler(NULL, TRUE) during
init which ignores CTRL_C_EVENT — clear this flag before registering the
handler so ConPTY-generated events reach it.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: branchseer

Cargo.lock

@@ -62,6 +62,7 @@ cow-utils = "0.1.3"
 crossterm = { version = "0.29.0", features = ["event-stream"] }
 csv-async = { version = "1.3.1", features = ["tokio"] }
 ctor = "0.6"
+ctrlc = "3.5.2"
 derive_more = "2.0.1"
 diff-struct = "0.5.3"
 directories = "6.0.0"

Cargo.toml

@@ -14,6 +14,7 @@ vt100 = { workspace = true }
 
 [dev-dependencies]
 ctor = { workspace = true }
+ctrlc = { workspace = true }
 ntest = "0.9.5"
 subprocess_test = { workspace = true, features = ["portable-pty"] }
 terminal_size = "0.4"

crates/pty_terminal/Cargo.toml

@@ -366,29 +366,10 @@ fn resize_terminal() {
 #[expect(clippy::print_stdout, reason = "subprocess test output")]
 fn send_ctrl_c_interrupts_process() {
     let cmd = CommandBuilder::from(command_for_fn!((), |(): ()| {
-        use std::io::{Write, stdin, stdout};
-        #[cfg(unix)]
-        use std::sync::Arc;
-        #[cfg(unix)]
-        use std::sync::atomic::{AtomicBool, Ordering};
-
-        #[cfg(unix)]
-        let interrupted = Arc::new(AtomicBool::new(false));
-        #[cfg(unix)]
-        let interrupted_clone = Arc::clone(&interrupted);
+        use std::io::{Write, stdout};
 
-        // Install SIGINT handler on Unix
-        #[cfg(unix)]
-        // SAFETY: The closure only performs an atomic store, which is signal-safe.
-        unsafe {
-            signal_hook::low_level::register(signal_hook::consts::SIGINT, move || {
-                interrupted_clone.store(true, Ordering::SeqCst);
-            })
-            .unwrap();
-        }
-
-        // On Windows, explicitly ensure Ctrl+C is NOT ignored, so that
-        // CTRL_C_EVENT terminates the process via the default handler.
+        // On Windows, clear the "ignore CTRL_C" flag set by Rust runtime
+        // so that CTRL_C_EVENT reaches the ctrlc handler.
         #[cfg(windows)]
         {
             // SAFETY: Declaring correct signature for SetConsoleCtrlHandler from kernel32.
@@ -399,29 +380,28 @@ fn send_ctrl_c_interrupts_process() {
                 ) -> i32;
             }
 
-            // SAFETY: Clearing the "ignore CTRL_C" flag so the default handler runs.
+            // SAFETY: Clearing the "ignore CTRL_C" flag so handlers are invoked.
             unsafe {
                 SetConsoleCtrlHandler(None, 0); // FALSE = remove ignore
             }
         }
 
+        ctrlc::set_handler(move || {
+            // Write directly and exit from the handler to avoid races.
+            use std::io::Write;
+            let _ = write!(std::io::stdout(), "INTERRUPTED");
+            let _ = std::io::stdout().flush();
+            std::process::exit(0);
+        })
+        .unwrap();
+
         println!("ready");
         stdout().flush().unwrap();
 
-        // Block on stdin. On Unix, SIGINT interrupts read_line. On Windows,
-        // CTRL_C_EVENT terminates the process via the default handler.
-        let mut input = std::string::String::new();
-        let _ = stdin().read_line(&mut input);
-
-        // On Unix, check if SIGINT was delivered via the signal handler.
-        // On Windows, this code is unreachable: the process is terminated
-        // by CTRL_C_EVENT before read_line returns.
-        #[cfg(unix)]
-        if interrupted.load(Ordering::SeqCst) {
-            println!("INTERRUPTED");
+        // Block until Ctrl+C handler exits the process.
+        loop {
+            std::thread::park();
         }
-
-        stdout().flush().unwrap();
     }));
 
     let mut terminal = Terminal::spawn(ScreenSize { rows: 80, cols: 80 }, cmd).unwrap();
@@ -432,23 +412,10 @@ fn send_ctrl_c_interrupts_process() {
     // Send Ctrl+C
     terminal.send_ctrl_c().unwrap();
 
-    // On Unix, send newline to unblock read_line and verify SIGINT detection.
-    #[cfg(unix)]
-    {
-        terminal.write(b"\n").unwrap();
-        terminal.read_until("INTERRUPTED").unwrap();
-    }
+    // Verify interruption was detected
+    terminal.read_until("INTERRUPTED").unwrap();
 
-    let status = terminal.read_to_end().unwrap();
-
-    // On Unix, the process exits normally after detecting SIGINT.
-    #[cfg(unix)]
-    assert!(status.success());
-
-    // On Windows, the default CTRL_C handler calls ExitProcess with
-    // STATUS_CONTROL_C_EXIT, resulting in a non-zero exit code.
-    #[cfg(windows)]
-    assert!(!status.success());
+    let _ = terminal.read_to_end().unwrap();
 }
 
 #[test]