fix: preserve sessions after interrupted pane exits (#3418)

* fix: preserve sessions when pane shells are signaled

refs #3415

* fix: preserve shutdown checkpoints across platforms

refs #3415

---------

Co-authored-by: Jonathan Liebig <jonathan.liebig@gmail.com>

3 files changed, 66 insertions, 0 deletions

diff --git a/src/platform/mod.rs b/src/platform/mod.rs
index 86a431aa..d48ad4fa 100644
--- a/src/platform/mod.rs
+++ b/src/platform/mod.rs
@@ -25,6 +25,36 @@ pub enum Signal {
     Kill,
 }
 
+/// Why a pane runtime ended, before application persistence policy is applied.
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum ChildExitReason {
+    Exited,
+    Interrupted,
+    /// Imported runtimes have no child wait handle in the replacement server.
+    #[cfg(unix)]
+    Handoff,
+    WaitFailed,
+}
+
+impl ChildExitReason {
+    pub(crate) fn requires_session_checkpoint(self) -> bool {
+        match self {
+            Self::Interrupted => true,
+            #[cfg(unix)]
+            Self::Handoff => true,
+            _ => false,
+        }
+    }
+}
+
+#[cfg(unix)]
+pub(crate) use unix_common::classify_child_exit;
+
+#[cfg(not(any(unix, windows)))]
+pub(crate) fn classify_child_exit(_status: &portable_pty::ExitStatus) -> ChildExitReason {
+    ChildExitReason::Exited
+}
+
 pub(crate) fn detached_custom_command_process(command: &str) -> std::process::Command {
     let mut process = detached_custom_command_process_platform(command);
     configure_background_command(&mut process);
@@ -415,6 +445,25 @@ impl PrefixInputSource for RealPrefixInputSource {
     }
 }
 
+#[cfg(all(test, any(unix, windows)))]
+#[test]
+fn child_exit_classification_only_checkpoints_interruptions() {
+    for code in [0, 1, 130, 255, 0xC0000005] {
+        let reason = classify_child_exit(&portable_pty::ExitStatus::with_exit_code(code));
+        assert_eq!(reason, ChildExitReason::Exited, "exit code {code:#x}");
+        assert!(!reason.requires_session_checkpoint());
+    }
+    #[cfg(windows)]
+    let status = portable_pty::ExitStatus::with_exit_code(0xC000013A);
+    #[cfg(not(windows))]
+    let status = portable_pty::ExitStatus::with_signal("Terminated: 15");
+    assert_eq!(classify_child_exit(&status), ChildExitReason::Interrupted);
+    assert!(classify_child_exit(&status).requires_session_checkpoint());
+    #[cfg(unix)]
+    assert!(ChildExitReason::Handoff.requires_session_checkpoint());
+    assert!(!ChildExitReason::WaitFailed.requires_session_checkpoint());
+}
+
 #[cfg(all(test, unix))]
 mod tests {
     use super::*;
diff --git a/src/platform/unix_common.rs b/src/platform/unix_common.rs
index dff67357..104f6b69 100644
--- a/src/platform/unix_common.rs
+++ b/src/platform/unix_common.rs
@@ -1,5 +1,13 @@
 use std::path::{Path, PathBuf};
 
+pub(crate) fn classify_child_exit(status: &portable_pty::ExitStatus) -> super::ChildExitReason {
+    if status.signal().is_some() {
+        super::ChildExitReason::Interrupted
+    } else {
+        super::ChildExitReason::Exited
+    }
+}
+
 pub(crate) fn wait_client_stream_readable(stream: &crate::ipc::LocalStream) -> std::io::Result<()> {
     use std::os::fd::{AsFd as _, AsRawFd as _};
     let crate::ipc::LocalStream::UdSocket(stream) = stream;
diff --git a/src/platform/windows.rs b/src/platform/windows.rs
index ce0afedb..4deb1864 100644
--- a/src/platform/windows.rs
+++ b/src/platform/windows.rs
@@ -15,6 +15,15 @@ use std::{
 
 mod clipboard_image;
 
+pub(crate) fn classify_child_exit(status: &portable_pty::ExitStatus) -> super::ChildExitReason {
+    // STATUS_CONTROL_C_EXIT is reported without a Unix signal by portable-pty.
+    if status.exit_code() == 0xC000013A {
+        super::ChildExitReason::Interrupted
+    } else {
+        super::ChildExitReason::Exited
+    }
+}
+
 pub(crate) fn wait_client_stream_readable(
     _stream: &crate::ipc::LocalStream,
 ) -> std::io::Result<()> {