feat: restore tabs and splits at launch

The tab layout (tab order and names, pins, the active tab, split trees
with their ratios) is saved whenever it changes — checked once a second,
written only on change, so it survives a crash — and reopened at the
next launch: saved profiles reconnect and local shells start in the
directory they were in (on Linux the live /proc cwd, so it isn't one
command behind). Quick Connect tabs and placeholder panes are skipped.
A General setting turns it off; it never runs when launched with
--connect, --run-local or --open, and screenshot runs never save.

Verified: a local tab left in /usr/share came back there with a
'Restored 1 tab(s)' toast.

rust/app/src/app.rs

@@ -121,6 +121,9 @@ pub enum InputThen {
 
 pub struct App {
     pub s: Shared,
+    /// The tab layout as last saved for restoring (see restore.rs), and when it was last checked.
+    pub saved_layout: Option<String>,
+    layout_checked: f64,
     rx: mpsc::Receiver<Event>,
     pub theme: ThemeKind,
     pub editor: profile_editor::ProfileEditor,
@@ -195,7 +198,13 @@ impl App {
             answers: opts.answers,
             run_local: opts.run_local.map(|c| (c, None)),
             resize_sidebar: false,
+            saved_layout: None,
+            layout_checked: 0.0,
         };
+        let restore = opts.connect.is_empty() && app.run_local.is_none() && opts.open.is_none() && app.s.prefs.restore_sessions;
+        if restore {
+            crate::restore::restore(&mut app);
+        }
         for c in &opts.connect {
             match app.s.profiles.iter().find(|p| &p.id == c || &p.display_name == c).map(|p| p.id.clone()) {
                 Some(id) => app.connect_profile(&id, true),
@@ -1003,6 +1012,10 @@ impl eframe::App for App {
         chrome::palette(self, &ctx);
         chrome::toasts(self, &ctx);
         self.screenshot(&ctx);
+        if self.screenshot.is_none() && self.s.prefs.restore_sessions && self.s.now - self.layout_checked > 1.0 {
+            self.layout_checked = self.s.now;
+            crate::restore::save_if_changed(self);
+        }
         chrome::resize_edges(&ctx);
         // Requests raised while drawing are handled on the next frame.
         if !self.s.requests.is_empty() {

rust/app/src/main.rs

@@ -13,6 +13,7 @@ mod profile_editor;
 mod quick_connect;
 mod raw_view;
 mod recordings;
+mod restore;
 mod settings;
 mod sftp;
 mod sidebar;

rust/app/src/restore.rs

@@ -0,0 +1,184 @@
+//! Reopens the previous run's tabs and splits at launch: saved profiles reconnect, local shells
+//! start again in the directory they were in. The layout is saved whenever it changes (not only on
+//! exit), so it survives a crash. Quick Connect tabs aren't restored (they have no saved profile).
+
+use crate::app::App;
+use crate::splits::{Dir, Split};
+use crate::state::Tab;
+use nexus_core::models::Protocol;
+use serde::{Deserialize, Serialize};
+use std::path::PathBuf;
+
+const KEY: &str = "session_layout";
+
+#[derive(Serialize, Deserialize, PartialEq, Debug, Default)]
+pub struct Saved {
+    tabs: Vec<SavedTab>,
+    active: usize,
+}
+
+#[derive(Serialize, Deserialize, PartialEq, Debug)]
+struct SavedTab {
+    name: String,
+    pinned: bool,
+    layout: Layout,
+}
+
+#[derive(Serialize, Deserialize, PartialEq, Debug)]
+#[serde(tag = "kind", rename_all = "camelCase")]
+enum Layout {
+    Profile {
+        id: String,
+    },
+    Local {
+        shell: String,
+        cwd: Option<PathBuf>,
+    },
+    /// A split pane still showing the connection picker, or a session that can't be restored.
+    Empty,
+    Split {
+        down: bool,
+        ratio: f32,
+        a: Box<Layout>,
+        b: Box<Layout>,
+    },
+}
+
+fn session_layout(app: &App, id: &str) -> Layout {
+    let Some(pane) = app.s.pane(id) else { return Layout::Empty };
+    if pane.info.protocol == Protocol::Local {
+        let (shell, cwd) = app.s.svc.sessions.local_state(id).unwrap_or_default();
+        return Layout::Local { shell, cwd };
+    }
+    match app.s.profile(&pane.info.profile_id) {
+        Some(p) => Layout::Profile { id: p.id.clone() },
+        None => Layout::Empty,
+    }
+}
+
+fn split_layout(app: &App, sp: &Split) -> Layout {
+    match sp {
+        Split::Leaf(Some(id)) => session_layout(app, id),
+        Split::Leaf(None) => Layout::Empty,
+        Split::Node { dir, ratio, a, b } => {
+            Layout::Split { down: *dir == Dir::Down, ratio: *ratio, a: Box::new(split_layout(app, a)), b: Box::new(split_layout(app, b)) }
+        }
+    }
+}
+
+pub fn capture(app: &App) -> Saved {
+    let tabs: Vec<SavedTab> = app
+        .s
+        .tabs
+        .iter()
+        .map(|t| {
+            let info = app.s.pane(&t.id).map(|p| (p.info.tab_name.clone(), p.info.pinned)).unwrap_or_default();
+            let layout = match &t.split {
+                Some(sp) => split_layout(app, sp),
+                None => session_layout(app, &t.id),
+            };
+            SavedTab { name: info.0, pinned: info.1, layout }
+        })
+        .filter(|t| t.layout != Layout::Empty)
+        .collect();
+    let active = app.s.tabs.iter().position(|t| Some(&t.id) == app.s.active.as_ref()).unwrap_or(0);
+    Saved { active: active.min(tabs.len().saturating_sub(1)), tabs }
+}
+
+/// Saves the layout if it changed since the last save (called each frame; cheap for a few tabs).
+pub fn save_if_changed(app: &mut App) {
+    let Ok(json) = serde_json::to_string(&capture(app)) else { return };
+    if app.saved_layout.as_deref() != Some(&json) {
+        let _ = app.s.svc.store.set_setting(KEY, &json);
+        app.saved_layout = Some(json);
+    }
+}
+
+/// Opens one session for a layout leaf; returns its id.
+fn open(app: &mut App, l: &Layout) -> Option<String> {
+    let id = match l {
+        Layout::Profile { id } => app.s.svc.connect_profile(id).ok()?,
+        Layout::Local { shell, cwd } => app.s.svc.connect_local_in(shell, cwd.clone()),
+        _ => return None,
+    };
+    app.add_session(&id, false);
+    Some(id)
+}
+
+fn build(app: &mut App, l: &Layout) -> Split {
+    match l {
+        Layout::Split { down, ratio, a, b } => Split::Node {
+            dir: if *down { Dir::Down } else { Dir::Right },
+            ratio: ratio.clamp(0.1, 0.9),
+            a: Box::new(build(app, a)),
+            b: Box::new(build(app, b)),
+        },
+        leaf => Split::Leaf(open(app, leaf)),
+    }
+}
+
+pub fn restore(app: &mut App) {
+    let Some(saved) = app.s.svc.store.setting(KEY).and_then(|j| serde_json::from_str::<Saved>(&j).ok()) else { return };
+    let mut ids = vec![];
+    for t in &saved.tabs {
+        let (id, split) = match &t.layout {
+            Layout::Split { .. } => {
+                let sp = build(app, &t.layout);
+                let Some(first) = sp.sessions().first().cloned() else { continue };
+                (first, Some(sp))
+            }
+            leaf => match open(app, leaf) {
+                Some(id) => (id, None),
+                None => continue,
+            },
+        };
+        if !t.name.is_empty() {
+            let _ = app.s.svc.sessions.rename(&id, &t.name);
+            if let Some(p) = app.s.pane_mut(&id) {
+                p.info.tab_name = t.name.clone();
+            }
+        }
+        if t.pinned {
+            let _ = app.s.svc.sessions.pin(&id, true);
+            if let Some(p) = app.s.pane_mut(&id) {
+                p.info.pinned = true;
+            }
+        }
+        app.s.tabs.push(Tab { id: id.clone(), activity: false, split });
+        ids.push(id);
+    }
+    if let Some(id) = ids.get(saved.active).or(ids.first()) {
+        app.s.active = Some(id.clone());
+        app.s.focused = Some(id.clone());
+    }
+    if !ids.is_empty() {
+        app.s.info(format!("Restored {} tab(s) from last time", ids.len()));
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn layouts_round_trip() {
+        let saved = Saved {
+            active: 1,
+            tabs: vec![
+                SavedTab { name: "web".into(), pinned: true, layout: Layout::Profile { id: "p1".into() } },
+                SavedTab {
+                    name: String::new(),
+                    pinned: false,
+                    layout: Layout::Split {
+                        down: true,
+                        ratio: 0.3,
+                        a: Box::new(Layout::Local { shell: "/bin/zsh".into(), cwd: Some("/tmp".into()) }),
+                        b: Box::new(Layout::Empty),
+                    },
+                },
+            ],
+        };
+        let json = serde_json::to_string(&saved).unwrap();
+        assert_eq!(serde_json::from_str::<Saved>(&json).unwrap(), saved);
+    }
+}

rust/app/src/settings.rs

@@ -249,6 +249,9 @@ impl Settings {
             field(ui, "Confirm on disconnect");
             ui.checkbox(&mut p.confirm_on_disconnect, "Ask before disconnecting sessions");
             ui.end_row();
+            field(ui, "Restore tabs");
+            ui.checkbox(&mut p.restore_sessions, "Reopen last session's tabs and splits at launch");
+            ui.end_row();
             field(ui, "Remote clipboard");
             ui.checkbox(&mut p.allow_remote_clipboard, "Let remote hosts set the clipboard (OSC 52, VNC)");
             ui.end_row();