refactor: simplify live handoff setup

refs #3651

src/pane.rs

@@ -1303,10 +1303,6 @@ impl PaneRuntimeIo {
     }
 
     #[cfg(windows)]
-    #[cfg_attr(
-        windows,
-        allow(dead_code, reason = "used by the stacked Windows handoff integration")
-    )]
     fn windows_handoff_supported(&self) -> bool {
         match self {
             PaneRuntimeIo::Actor(actor) => actor.supports_handoff(),
@@ -1316,10 +1312,6 @@ impl PaneRuntimeIo {
     }
 
     #[cfg(windows)]
-    #[cfg_attr(
-        windows,
-        allow(dead_code, reason = "used by the stacked Windows handoff integration")
-    )]
     fn duplicate_windows_handoff(
         &self,
         target: &std::process::Child,
@@ -1343,10 +1335,6 @@ impl PaneRuntimeIo {
     }
 
     #[cfg(any(unix, windows))]
-    #[cfg_attr(
-        windows,
-        allow(dead_code, reason = "used by the stacked Windows handoff integration")
-    )]
     fn begin_handoff(&self, timeout: std::time::Duration) -> std::io::Result<()> {
         match self {
             PaneRuntimeIo::Actor(actor) => actor.begin_handoff(timeout),
@@ -1356,10 +1344,6 @@ impl PaneRuntimeIo {
     }
 
     #[cfg(any(unix, windows))]
-    #[cfg_attr(
-        windows,
-        allow(dead_code, reason = "used by the stacked Windows handoff integration")
-    )]
     fn set_handoff_paused(&self, paused: bool) -> std::io::Result<()> {
         match self {
             PaneRuntimeIo::Actor(actor) => {
@@ -1375,10 +1359,6 @@ impl PaneRuntimeIo {
     }
 
     #[cfg(any(unix, windows))]
-    #[cfg_attr(
-        windows,
-        allow(dead_code, reason = "used by the stacked Windows handoff integration")
-    )]
     fn release_after_commit(&self) -> std::io::Result<()> {
         match self {
             PaneRuntimeIo::Actor(actor) => actor.release_after_commit(),
@@ -1928,19 +1908,11 @@ impl PaneRuntime {
     }
 
     #[cfg(windows)]
-    #[cfg_attr(
-        windows,
-        allow(dead_code, reason = "used by the stacked Windows handoff integration")
-    )]
     pub(crate) fn windows_handoff_supported(&self) -> bool {
         self.io.windows_handoff_supported()
     }
 
     #[cfg(windows)]
-    #[cfg_attr(
-        windows,
-        allow(dead_code, reason = "used by the stacked Windows handoff integration")
-    )]
     pub(crate) fn duplicate_windows_handoff(
         &self,
         target: &std::process::Child,
@@ -1949,10 +1921,6 @@ impl PaneRuntime {
     }
 
     #[cfg(any(unix, windows))]
-    #[cfg_attr(
-        windows,
-        allow(dead_code, reason = "used by the stacked Windows handoff integration")
-    )]
     pub fn preserve_for_handoff(mut self) {
         if let Err(err) = self.io.release_after_commit() {
             warn!(
@@ -1990,10 +1958,6 @@ impl PaneRuntime {
     }
 
     #[cfg(any(unix, windows))]
-    #[cfg_attr(
-        windows,
-        allow(dead_code, reason = "used by the stacked Windows handoff integration")
-    )]
     pub fn set_handoff_reader_paused(&self, paused: bool) {
         if let Err(err) = self.io.set_handoff_paused(paused) {
             warn!(
@@ -2006,10 +1970,6 @@ impl PaneRuntime {
     }
 
     #[cfg(any(unix, windows))]
-    #[cfg_attr(
-        windows,
-        allow(dead_code, reason = "used by the stacked Windows handoff integration")
-    )]
     pub fn pause_handoff_reader(&self, timeout: std::time::Duration) -> std::io::Result<()> {
         self.io.begin_handoff(timeout)
     }

src/server/handoff.rs

@@ -331,7 +331,6 @@ pub(crate) fn accept_windows_handoff(
     panes: Vec<crate::pty::backend::WindowsPtyHandoff>,
     listeners: [crate::platform::WindowsListenerHandoff; 2],
 ) -> io::Result<HandoffStream> {
-    crate::platform::ensure_same_process_session(child.id())?;
     let deadline = std::time::Instant::now() + READY_TIMEOUT;
     let stream = loop {
         match listener.accept() {

src/server/headless/bootstrap.rs

@@ -190,16 +190,13 @@ fn run_handoff_import_server(socket_path: &Path, token: &str) -> io::Result<()>
                 event_hub.clone(),
                 should_quit.clone(),
             )?;
-            let mut server = HeadlessServer::new(
+            let server = HeadlessServer::new(
                 app,
                 &loaded_config.diagnostics,
                 Some(api_tx.clone()),
                 Some(api_server),
                 should_quit,
             )?;
-            // Carried across before any client attaches, so the first title sent is
-            // the override rather than the configured one it replaced.
-            server.api_window_title = received.manifest.api_window_title.clone();
             crate::server::handoff::report_ready(&mut received.stream)?;
             crate::server::handoff::wait_committed(&mut received.stream)?;
             server

src/server/headless/lifecycle.rs

@@ -113,14 +113,11 @@ impl HeadlessServer {
                 params.expected_version,
                 self.api_window_title.clone(),
             );
-            import_child = Some(handoff::spawn_handoff_import(
+            let child = import_child.insert(handoff::spawn_handoff_import(
                 params.import_exe.as_deref().map(Path::new),
                 &socket_path,
                 &token,
             )?);
-            let child = import_child
-                .as_ref()
-                .ok_or_else(|| io::Error::other("replacement child unavailable"))?;
             #[cfg(windows)]
             let mut stream = {
                 crate::platform::ensure_same_process_session(child.id())?;