Add multiplexer detach/resume (#407)

rootshell/App/AppCommands.swift

@@ -661,6 +661,14 @@ struct WindowCommands: Commands {
             }
             .modifier(DynamicShortcut(action: .discover_sessions, shortcuts: shortcutState.shortcuts))
 
+            Button("Detach Session") {
+                UIApplication.shared.sendAction(
+                    #selector(Ghostty.TerminalView.menuDetachSession(_:)),
+                    to: nil, from: nil, for: nil
+                )
+            }
+            .modifier(DynamicShortcut(action: .detach_session, shortcuts: shortcutState.shortcuts))
+
             Button("Detach Other Clients") {
                 UIApplication.shared.sendAction(
                     #selector(Ghostty.TerminalView.menuDetachOtherClients(_:)),

rootshell/App/CatalystAppDelegate.swift

@@ -348,6 +348,10 @@ extension UIApplication {
         sendAction(#selector(Ghostty.TerminalView.menuDiscoverSessions(_:)), to: nil, from: sender, for: nil)
     }
 
+    @objc func ghostty_detachSession(_ sender: Any?) {
+        sendAction(#selector(Ghostty.TerminalView.menuDetachSession(_:)), to: nil, from: sender, for: nil)
+    }
+
     @objc func ghostty_detachOtherClients(_ sender: Any?) {
         sendAction(#selector(Ghostty.TerminalView.menuDetachOtherClients(_:)), to: nil, from: sender, for: nil)
     }
@@ -1481,6 +1485,11 @@ class CatalystAppDelegate: AppDelegate {
             modifierFlags: [.command, .control]
         )
 
+        let detachSession = UICommand(
+            title: String(localized: "Detach Session"),
+            action: #selector(UIApplication.ghostty_detachSession(_:))
+        )
+
         let detachOtherClients = UIKeyCommand(
             title: String(localized: "Detach Other Clients"),
             action: #selector(UIApplication.ghostty_detachOtherClients(_:)),
@@ -1511,7 +1520,7 @@ class CatalystAppDelegate: AppDelegate {
 
         let navGroup = UIMenu(title: "", options: .displayInline, children: [
             toggleTabSwitcher, toggleTabExpose, previousTab, nextTab, previousGroup, nextGroup, tmuxSessions,
-            discoverSessions, detachOtherClients
+            discoverSessions, detachSession, detachOtherClients
         ])
 
         // Tab selection (1-9), each with its own action (see ghostty_selectTabN).

rootshell/App/UIApplication+CommandFallback.swift

@@ -250,6 +250,10 @@ extension UIApplication {
         ghostty_postNotification(.discoverSessions)
     }
 
+    @objc func menuDetachSession(_ sender: Any?) {
+        ghostty_postNotification(.detachSession)
+    }
+
     @objc func menuDetachOtherClients(_ sender: Any?) {
         ghostty_postNotification(.detachOtherClients)
     }

rootshell/Core/Keybinds/KeybindAction.swift

@@ -102,6 +102,8 @@ enum KeybindAction: String, CaseIterable, Codable, Identifiable, Hashable {
     case show_tmux_sessions = "show_tmux_sessions"
     /// Re-run multiplexer session discovery on the focused terminal
     case discover_sessions = "discover_sessions"
+    /// Detach the current tab from its multiplexer (tmux / zellij / herdr / zmx)
+    case detach_session = "detach_session"
     /// Detach all OTHER tmux clients from the current gateway
     /// (`detach-client -a`); on a herdr tab, take the whole session instead
     case detach_other_clients = "detach_other_clients"
@@ -303,7 +305,7 @@ enum KeybindAction: String, CaseIterable, Codable, Identifiable, Hashable {
 
         case .new_local_shell, .new_tab, .new_window, .close_tab, .duplicate_ssh_tab,
              .previous_tab, .next_tab, .show_tmux_sessions, .discover_sessions,
-             .detach_other_clients, .toggle_tab_switcher,
+             .detach_session, .detach_other_clients, .toggle_tab_switcher,
              .toggle_tab_expose, .previous_group, .next_group, .select_tab_1, .select_tab_2, .select_tab_3, .select_tab_4, .select_tab_5,
              .select_tab_6, .select_tab_7, .select_tab_8, .select_tab_9:
             return .tabs
@@ -362,6 +364,7 @@ enum KeybindAction: String, CaseIterable, Codable, Identifiable, Hashable {
         case .next_tab: return String(localized: "Next Tab", comment: "Keybind action")
         case .show_tmux_sessions: return String(localized: "Sessions & Workspaces", comment: "Keybind action")
         case .discover_sessions: return String(localized: "Discover Sessions", comment: "Keybind action")
+        case .detach_session: return String(localized: "Detach Session", comment: "Keybind action: leave multiplexer, keep session")
         case .detach_other_clients: return String(localized: "Detach Other Clients", comment: "Keybind action")
 
         case .select_tab_1: return String(localized: "Select Tab 1", comment: "Keybind action")
@@ -462,6 +465,7 @@ enum KeybindAction: String, CaseIterable, Codable, Identifiable, Hashable {
         case .next_tab: return .nextTab
         case .show_tmux_sessions: return .showTmuxSessions
         case .discover_sessions: return .discoverSessions
+        case .detach_session: return .detachSession
         case .detach_other_clients: return .detachOtherClients
         case .select_tab_1, .select_tab_2, .select_tab_3, .select_tab_4, .select_tab_5,
              .select_tab_6, .select_tab_7, .select_tab_8, .select_tab_9:
@@ -618,7 +622,7 @@ enum KeybindAction: String, CaseIterable, Codable, Identifiable, Hashable {
              .browse_profiles, .toggle_ai_agent, .toggle_voice_agent, .toggle_tab_bar, .toggle_group_mode, .toggle_transparency,
              .toggle_titlebar, .toggle_auto_redact,
              .toggle_background_effect, .toggle_tab_switcher, .toggle_tab_expose, .show_tmux_sessions,
-             .discover_sessions, .detach_other_clients,
+             .discover_sessions, .detach_session, .detach_other_clients,
              .increase_font_size, .decrease_font_size,
              .reset_font_size, .start_search:
             return true

rootshell/Core/Keybinds/KeybindCommandGenerator.swift

@@ -129,7 +129,7 @@ final class KeybindCommandGenerator: ObservableObject {
              .toggle_split_zoom, .equalize_splits, .open_settings, .toggle_quick_settings, .browse_hosts,
              .browse_profiles, .toggle_ai_agent, .toggle_voice_agent, .toggle_tab_bar, .toggle_group_mode, .toggle_tab_switcher,
              .toggle_tab_expose, .previous_group, .next_group, .show_tmux_sessions, .discover_sessions,
-             .detach_other_clients,
+             .detach_session, .detach_other_clients,
              .toggle_transparency, .toggle_titlebar, .toggle_auto_redact, .toggle_background_effect, .toggle_compose,
              .toggle_full_screen, .toggle_mouse_capture, .cycle_input_source,
              .increase_font_size, .decrease_font_size,

rootshell/Core/Terminal/TerminalSessionController.swift

@@ -1101,15 +1101,15 @@ final class TerminalSessionController {
     /// For resumable sessions (Trzsz/Mosh, and local sessions with an active
     /// embedded session) the `reason` drives whether we tell the server to
     /// close: `.sceneTeardown` keeps the server-side session alive so resume
-    /// can pick it back up; `.userClose`/`.transferOut` terminate it.
+    /// can pick it back up; `.userClose`/`.muxDetach`/`.transferOut` terminate it.
     func teardown(reason: Ghostty.TerminalView.CleanupReason) {
         localSessionCreateGeneration &+= 1
         responsePipeline.cancel()
         historyRecorder.cancel()
 
         if let trzszSession = session as? TrzszSession {
             switch reason {
-            case .userClose:
+            case .userClose, .muxDetach:
                 trzszSession.terminate()
             case .sceneTeardown:
                 trzszSession.stopForReconnect()
@@ -1118,7 +1118,7 @@ final class TerminalSessionController {
             }
         } else if let moshSession = session as? MoshSession {
             switch reason {
-            case .userClose, .transferOut:
+            case .userClose, .muxDetach, .transferOut:
                 // Mosh has no peer-attach concept, so a transferOut on a
                 // mosh session would be a logic bug; treat it as a user
                 // close so we don't leave a zombie server session.

rootshell/Features/Herdr/HerdrController.swift

@@ -780,9 +780,19 @@ final class HerdrController {
 
     /// User-initiated detach: ends control mode, optionally closing the
     /// gateway tab too. The herdr session keeps running on the host.
-    func detach(closeGateway: Bool) {
+    func detach(closeGateway: Bool, announce: Bool = true) {
         let gatewayView = gateway
         let windowId = hostWindowId
+        // Same choke point as tmux `requestGracefulDetach`: menu, ESC, and
+        // Detach Session all show the reconnect banner.
+        if announce, isActive || !didEnd {
+            MuxSessionDetach.notifyControlModeDetached(
+                type: .herdr,
+                sessionName: sessionName,
+                windowId: windowId,
+                terminal: gatewayView
+            )
+        }
         stop()
         guard closeGateway, let gatewayView else { return }
         // Same routing a dying tab uses: the .closeSplit observer resolves

rootshell/Features/Multiplexer/MuxDetachBannerState.swift

@@ -0,0 +1,14 @@
+//
+//  MuxDetachBannerState.swift
+//  rootshell
+//
+//  Transient banner after mux detach (or when focusing an already-live
+//  attachment) with an optional Reconnect action.
+//
+
+import Foundation
+
+struct MuxDetachBannerState: Equatable {
+    let message: String
+    let offer: MuxSessionResume.ReconnectOffer?
+}