feat(terminal-launch): spawn new sessions into tmux pane when in TMUX (#74)

crates/jcode-terminal-launch/src/lib.rs

@@ -112,6 +112,12 @@ pub fn detected_resume_terminal() -> Option<String> {
     {
         return Some("handterm".to_string());
     }
+    // tmux: prefer splitting a new pane in the existing session over launching
+    // a brand-new terminal emulator. Detected via $TMUX which tmux always sets
+    // for processes inside an attached session. See issue #74 / upstream PR #78.
+    if std::env::var("TMUX").is_ok() {
+        return Some("tmux".to_string());
+    }
     if std::env::var("KITTY_PID").is_ok() {
         return Some("kitty".to_string());
     }
@@ -176,6 +182,7 @@ pub fn resume_terminal_candidates() -> Vec<String> {
     #[cfg(target_os = "macos")]
     {
         for term in [
+            "tmux",
             "ghostty",
             "kitty",
             "wezterm",
@@ -193,6 +200,7 @@ pub fn resume_terminal_candidates() -> Vec<String> {
     {
         for term in [
             "handterm",
+            "tmux",
             "kitty",
             "wezterm",
             "alacritty",
@@ -266,6 +274,18 @@ fn build_spawn_command(term: &str, command: &TerminalCommand, cwd: &Path) -> Opt
             let shell = shell_command(&command_parts(command));
             cmd.args(["--backend", "gpu", "--exec", &shell]);
         }
+        #[cfg(unix)]
+        "tmux" => {
+            // Split the current tmux window into a new detached pane and run
+            // the requested command there. `-d` keeps focus on the current
+            // pane; `select-layout tiled` re-flows so the new pane is visible.
+            // See issue #74 / upstream PR #78.
+            let shell = shell_command(&command_parts(command));
+            cmd.args(["split-window", "-d", "-c"])
+                .arg(cwd)
+                .arg(&shell)
+                .args([";", "select-layout", "tiled"]);
+        }
         #[cfg(target_os = "macos")]
         "ghostty" => {
             let shell = shell_command(&command_parts(command));
@@ -375,6 +395,34 @@ mod tests {
         }
     }
 
+    #[test]
+    #[cfg(unix)]
+    fn detected_resume_terminal_recognizes_tmux_via_tmux_env() {
+        // Regression for issue #74 / upstream PR #78: an attached tmux session
+        // must be detected so spawn_resume_in_new_terminal opens a new pane in
+        // the existing session instead of launching a fresh terminal emulator.
+        let _guard = ENV_LOCK.lock().unwrap();
+        let prev_tmux = std::env::var_os("TMUX");
+        unsafe {
+            // Clear the higher-priority detectors so tmux can win.
+            std::env::remove_var("HANDTERM_SESSION");
+            std::env::remove_var("HANDTERM_PID");
+            std::env::remove_var("KITTY_PID");
+            std::env::remove_var("WEZTERM_EXECUTABLE");
+            std::env::remove_var("WEZTERM_PANE");
+            std::env::remove_var("ALACRITTY_WINDOW_ID");
+            std::env::remove_var("GHOSTTY_RESOURCES_DIR");
+            std::env::set_var("TMUX", "/tmp/tmux-1000/default,12345,0");
+        }
+        assert_eq!(detected_resume_terminal().as_deref(), Some("tmux"));
+        unsafe {
+            std::env::remove_var("TMUX");
+            if let Some(prev) = prev_tmux {
+                std::env::set_var("TMUX", prev);
+            }
+        }
+    }
+
     #[test]
     fn shell_command_quotes_arguments() {
         let shell = shell_command(&["jcode".to_string(), "it's ok".to_string()]);