cli: intercept Ctrl+C for deb, build and put

The SIGINT handler only records the interruption and wakes a watchdog
through a self-pipe (async-signal-safe); the watchdog runs the whole
shutdown in thread context — the live view's reporter first, then the
notice and the log hint, then the cleanup hooks, then exit 130. Flows
park in wait_for_shutdown instead of racing it with their own exit,
and an end-to-end test drives the sequence by re-spawning the test
binary and raising SIGINT at itself.

src/main.rs

@@ -20,6 +20,155 @@ fn current_dir_or_exit() -> std::path::PathBuf {
     }
 }
 
+/// CLI-side Ctrl+C wiring. The passive state (interrupted flag, cleanup
+/// hook registry, reporter slot) lives in `pkh::interrupt`; everything that
+/// installs, prints or exits lives here: the SIGINT handler only wakes a
+/// watchdog through a self-pipe (async-signal-safe), and the watchdog runs
+/// the whole shutdown in thread context — the live view's reporter clears
+/// the terminal, the notice is printed, further Ctrl+C is absorbed as a
+/// no-op, the cleanup hooks release their resources, and the process exits
+/// with the conventional status 130, skipping destructors.
+mod interrupt {
+    use std::sync::atomic::{AtomicBool, AtomicI32, Ordering};
+
+    /// Whether the interrupt notice has been shown; the first caller prints
+    /// it, later ones stay silent
+    static NOTICE_SHOWN: AtomicBool = AtomicBool::new(false);
+
+    /// Whether handler, self-pipe and watchdog are in place
+    static INSTALLED: AtomicBool = AtomicBool::new(false);
+
+    /// Write end of the self-pipe the signal handler wakes the watchdog
+    /// through; `-1` until [`install`] set it up
+    static SELF_PIPE_WRITE: AtomicI32 = AtomicI32::new(-1);
+
+    /// Install the process-global Ctrl+C (SIGINT) handler; idempotent.
+    ///
+    /// When the self-pipe or the watchdog cannot be set up, the default
+    /// SIGINT disposition is kept (the process dies immediately) rather
+    /// than installing a handler that could not run the shutdown.
+    pub fn install() {
+        if INSTALLED.swap(true, Ordering::SeqCst) {
+            return;
+        }
+
+        let mut fds = [0 as libc::c_int; 2];
+        // SAFETY: pipe(2) into a two-element array we own
+        if unsafe { libc::pipe(fds.as_mut_ptr()) } != 0 {
+            INSTALLED.store(false, Ordering::SeqCst);
+            return;
+        }
+        let (read_fd, write_fd) = (fds[0], fds[1]);
+
+        // The write end is used from the signal handler: non-blocking, so
+        // even a full pipe degrades to a dropped wake-up instead of
+        // blocking the handler.
+        // SAFETY: fcntl(2) on a pipe file descriptor we just created
+        unsafe {
+            let flags = libc::fcntl(write_fd, libc::F_GETFL);
+            libc::fcntl(write_fd, libc::F_SETFL, flags | libc::O_NONBLOCK);
+        }
+        SELF_PIPE_WRITE.store(write_fd, Ordering::SeqCst);
+
+        let spawned = std::thread::Builder::new()
+            .name("pkh-interrupt".to_string())
+            .spawn(move || watchdog(read_fd));
+        if spawned.is_err() {
+            // SAFETY: closing pipe file descriptors we just created
+            unsafe {
+                libc::close(read_fd);
+                libc::close(write_fd);
+            }
+            SELF_PIPE_WRITE.store(-1, Ordering::SeqCst);
+            INSTALLED.store(false, Ordering::SeqCst);
+            return;
+        }
+
+        // SAFETY: installing a signal handler whose body only records the
+        // interruption and writes to the self-pipe (async-signal-safe)
+        unsafe {
+            libc::signal(libc::SIGINT, on_sigint as *const () as usize);
+        }
+    }
+
+    /// Never returns: park the calling thread until the watchdog exits the
+    /// process
+    ///
+    /// The watchdog owns the interrupt shutdown; a caller that would
+    /// otherwise reach its own `std::process::exit` and kill the process
+    /// mid-cleanup must park here instead.
+    pub fn wait_for_shutdown() -> ! {
+        loop {
+            std::thread::sleep(std::time::Duration::from_millis(100));
+        }
+    }
+
+    /// Signal handler body: record the interruption and wake the watchdog
+    /// through the self-pipe
+    extern "C" fn on_sigint(_sig: libc::c_int) {
+        pkh::interrupt::mark_interrupted();
+        let fd = SELF_PIPE_WRITE.load(Ordering::SeqCst);
+        if fd >= 0 {
+            // SAFETY: write(2) of one byte to the self-pipe is
+            // async-signal-safe; a failed write (e.g. EAGAIN) drops the
+            // wake-up instead of blocking the handler
+            unsafe {
+                libc::write(fd, b"x".as_ptr().cast(), 1);
+            }
+        }
+    }
+
+    /// Watchdog body: block until the signal handler's byte arrives, then
+    /// run the shutdown sequence
+    fn watchdog(read_fd: libc::c_int) {
+        let mut byte = [0u8; 1];
+        // SAFETY: read(2) into a local buffer of the announced length
+        let received = unsafe { libc::read(read_fd, byte.as_mut_ptr().cast(), 1) };
+        // The write end is never closed, so a short read cannot happen in
+        // practice; on error there is nothing to clean up either way.
+        if received > 0 {
+            run_interrupt_sequence();
+        }
+    }
+
+    /// Reporter, notice, cleanup hooks, exit 130: the whole shutdown, run
+    /// in the watchdog thread immediately on Ctrl+C — never in the signal
+    /// handler itself
+    ///
+    /// Further Ctrl+C while this runs writes bytes nobody reads: absorbed
+    /// as a no-op (send SIGTERM/SIGKILL if a hook ever hangs).
+    fn run_interrupt_sequence() {
+        let hint =
+            pkh::interrupt::take_reporter().and_then(|report| {
+                match std::panic::catch_unwind(std::panic::AssertUnwindSafe(report)) {
+                    Ok(hint) => hint,
+                    Err(_) => {
+                        log::error!("Interrupt reporter panicked");
+                        None
+                    }
+                }
+            });
+        show_notice();
+        if let Some(hint) = hint {
+            eprintln!("{hint}");
+        }
+        pkh::interrupt::run_cleanup_hooks();
+        // SAFETY: raw exit bypassing destructors, intended at interrupt time
+        unsafe {
+            libc::_exit(130);
+        }
+    }
+
+    /// Print the interrupt notice, once per process: the first caller
+    /// prints it, later ones stay silent
+    fn show_notice() {
+        if NOTICE_SHOWN.swap(true, Ordering::SeqCst) {
+            return;
+        }
+        eprintln!("CTRL+C: Build interrupted by user.");
+    }
+}
+
 fn main() {
     let rt = tokio::runtime::Runtime::new().unwrap();
     let logger =
@@ -513,6 +662,7 @@ fn main() {
         }
         Some(("build", sub_matches)) => {
             let cwd = current_dir_or_exit();
+            interrupt::install();
             let verbose = sub_matches
                 .get_one::<bool>("verbose")
                 .copied()
@@ -563,6 +713,11 @@ fn main() {
                     }
                 }
                 Err(e) => {
+                    // On Ctrl+C the interrupt watchdog owns the shutdown
+                    // (see `pkh deb`): park here instead of racing it
+                    if pkh::interrupt::interrupted() {
+                        interrupt::wait_for_shutdown();
+                    }
                     // The unmet-dependency diagnostics first, then the
                     // summary: the exact rendering the flow used to do.
                     if let Some(unmet) =
@@ -584,6 +739,7 @@ fn main() {
         }
         Some(("put", sub_matches)) => {
             let cwd = current_dir_or_exit();
+            interrupt::install();
             let ppa = sub_matches.get_one::<String>("ppa").map(|s| s.as_str());
             let changes = sub_matches
                 .get_one::<String>("changes")
@@ -613,12 +769,22 @@ fn main() {
                 prompter: &prompter,
             };
             if let Err(e) = rt.block_on(async { pkh::put::put(&options).await }) {
+                // On Ctrl+C the interrupt watchdog owns the shutdown (see
+                // `pkh deb`): park here instead of racing it
+                if pkh::interrupt::interrupted() {
+                    interrupt::wait_for_shutdown();
+                }
                 error!("{}", e);
                 std::process::exit(1);
             }
         }
         Some(("deb", sub_matches)) => {
             let cwd = current_dir_or_exit();
+            // Ctrl+C during the build must say what happened and release the
+            // ephemeral chroot instead of dying on the default disposition.
+            // The live view (when enabled) registers its own reporter on top
+            // of this to clear the widget first.
+            interrupt::install();
             let series = sub_matches.get_one::<String>("series").cloned();
             let pocket = sub_matches.get_one::<String>("pocket").cloned();
             let arch = sub_matches.get_one::<String>("arch").cloned();
@@ -685,6 +851,13 @@ fn main() {
             match result {
                 Ok(_) => info!("Done."),
                 Err(e) => {
+                    // On Ctrl+C the interrupt watchdog owns the shutdown: it
+                    // has already shown the notice, is releasing the build
+                    // resources, and will exit with 130 — park here instead
+                    // of racing it with another exit.
+                    if pkh::interrupt::interrupted() {
+                        interrupt::wait_for_shutdown();
+                    }
                     error!("{}", e);
                     std::process::exit(1);
                 }
@@ -816,3 +989,56 @@ fn main() {
         _ => unreachable!("Exhausted list of subcommands and subcommand_required prevents `None`"),
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use super::interrupt;
+
+    /// End-to-end check of the whole sequence: installed handler → self-pipe
+    /// → watchdog → notice + hooks → exit status 130. The sequence ends in
+    /// `libc::_exit`, so it cannot be exercised in-process: this test
+    /// re-spawns the test binary in child mode (env var), where the test
+    /// installs the handler and raises SIGINT at itself.
+    #[test]
+    fn sigint_sequence_prints_the_notice_and_exits_130() {
+        const CHILD_ENV: &str = "PKH_SIGINT_TEST_CHILD";
+        if std::env::var(CHILD_ENV).is_ok() {
+            // Child mode: install, register a pending hook, then interrupt
+            // ourselves. If the sequence never runs, the sleep below turns
+            // the failure into a wrong (zero) exit code instead of a hang.
+            interrupt::install();
+            // Alive until the watchdog drains it: a dropped guard would
+            // deregister the hook and the drain would run empty
+            let _hook = pkh::interrupt::register_cleanup_hook(Box::new(|| ()));
+            // SAFETY: kill(2) to our own process with SIGINT
+            unsafe {
+                libc::kill(libc::getpid(), libc::SIGINT);
+            }
+            std::thread::sleep(std::time::Duration::from_secs(30));
+            std::process::exit(0);
+        }
+
+        let exe = std::env::current_exe().expect("locate the test executable");
+        let output = std::process::Command::new(exe)
+            // --nocapture: libtest's capture buffer would otherwise swallow
+            // the watchdog's notice (threads spawned during a test inherit
+            // the capture), and the process exits before the harness prints
+            // anything it captured
+            .args([
+                "--exact",
+                "tests::sigint_sequence_prints_the_notice_and_exits_130",
+                "--test-threads=1",
+                "--nocapture",
+            ])
+            .env(CHILD_ENV, "1")
+            .output()
+            .expect("re-spawn the test binary");
+
+        let stderr = String::from_utf8_lossy(&output.stderr);
+        assert_eq!(output.status.code(), Some(130), "child stderr:\n{stderr}");
+        assert!(
+            stderr.contains("CTRL+C: Build interrupted by user."),
+            "child stderr:\n{stderr}"
+        );
+    }
+}