refactor(maestro): route web keys through a command registry

One entry per command — stable id, plain-language label, key chord, run()
— replacing the ad-hoc keydown listeners in main.ts, catalog.ts, debug.ts
and attach.ts and the parallel SHORTCUTS constant in help.ts. The `?`
overlay now renders the registry, so a binding and its documentation
cannot disagree.

Keys are canonicalised the way the TUI's `InputKey::canonical` spells
them, and chords resolve like its `ChordState`: hold while the sequence
is a strict prefix, otherwise dispatch. That gives the web a leader,
`ctrl-a` by default like `[tui].leader`, held as a partial chord and
`preventDefault`ed so it stops being select-all — the escape hatch in
docs/COMMAND-BAR.md needs somewhere to land (#149). The leader stays out
of real form fields, where select-all is still what the operator wants.

Same keys, same effects: plain single-key bindings remain deaf inside
form fields and the terminal's hidden textarea, chorded ones do not.

Refs #148

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

CLAUDE.md

@@ -36,10 +36,16 @@ optional.
 
 ## Where the work is
 
-Linear project **Maestro** under team **Naps62**.
+Gitea issues on [`naps62/maestro`](https://git.naps.pt/naps62/maestro), grouped
+into milestones.
 
-`.claude/linear.json` wires `/yolo` and `/work` to this project — they pick from
-"available now" (status backlog/pending, not blocked).
+`.claude/linear.json` (legacy filename, `tracker: gitea`) wires `/yolo` and
+`/work` to that tracker — they pick from open, unassigned issues whose
+dependencies are all closed. `/blitz <milestone>` sweeps a whole milestone.
+
+Labels carry one value per axis: `area/*`, `type/*`, `difficulty/*`.
+`difficulty` drives model selection downstream, so it tracks the shape of the
+work, not its size.
 
 ## Repo layout
 
@@ -72,11 +78,20 @@ before changing anything that creates or removes one.
 sidebars — line layout, activity colours, duration format, state precedence.
 Read it before changing sidebar rendering.
 
+`docs/PREVIEW.md` is the contract for what the content pane shows while the
+operator moves the sidebar highlight — what a preview may touch, what ends it,
+what commits it. Read it before changing sidebar-driven navigation.
+
 `docs/RESTART.md` is the contract for what clients do when the daemon restarts
 or is upgraded under them — the build stamp on `/api/info`, the status
 indicator's states, the blocking overlay, grace and poll timings. Read it
 before changing reconnect behaviour on either client.
 
+`docs/COMMAND-BAR.md` is the contract for the `ctrl-k` command bar in both
+clients — how it opens, the sigils, the key model, the match-and-rank algorithm
+the two matchers must agree on, and the fixture table they are tested against.
+Read it before changing either bar or either matcher.
+
 `nix run .#dev` (or `just dev`) brings up the whole local stack under
 process-compose: a debug daemon on 127.0.0.1:7071, then Vite on :5173 once the
 daemon answers `/api/info`. The SPA proxies `/api/*` back to the daemon, so only

crates/maestro-daemon/src/activity.rs

@@ -69,7 +69,7 @@ pub fn decide(idle_for: Duration, awaiting_input: bool) -> ActivityState {
 /// How long a session's pane must be continuously focused (a client's pane,
 /// not a sidebar highlight) before an `AwaitingInput` glow clears: the
 /// operator has looked, so the rail stops asking for attention.
-pub const FOCUS_CLEAR_HOLD: Duration = Duration::from_secs(5);
+pub const FOCUS_CLEAR_HOLD: Duration = Duration::from_secs(1);
 
 /// Downgrade `raw` from `AwaitingInput` to `Idle` once the pane has been
 /// focused for at least [`FOCUS_CLEAR_HOLD`].
@@ -161,7 +161,7 @@ mod tests {
     fn awaiting_input_glows_until_focus_hold_is_reached() {
         let now = std::time::Instant::now();
         let mut suppressed = false;
-        let since = now - (FOCUS_CLEAR_HOLD - Duration::from_secs(1));
+        let since = now - (FOCUS_CLEAR_HOLD - Duration::from_millis(200));
         assert_eq!(
             apply_focus_suppression(
                 ActivityState::AwaitingInput,

crates/maestro-tui/src/app.rs

@@ -11,7 +11,6 @@
 //! `dispatch` / the overlay routing.
 
 use std::collections::{HashMap, HashSet};
-use std::io::Stdout;
 use std::path::PathBuf;
 use std::time::Duration;
 
@@ -19,7 +18,6 @@ use chrono::Utc;
 use crossterm::event::{Event as CtEvent, EventStream};
 use futures_util::StreamExt;
 use maestro_protocol::{routes, BranchInfo, CreateSessionRequest, DaemonClient, NameBatch};
-use ratatui::backend::CrosstermBackend;
 use ratatui::Terminal;
 use uuid::Uuid;
 
@@ -89,8 +87,56 @@ pub struct App {
     /// that can move `Focus::Pane` (attach, tab switch, sidebar toggle,
     /// mouse) is covered without each one remembering to report it.
     focused_session: Option<Uuid>,
+    /// A sidebar highlight waiting for the pane's minimum gap before it
+    /// becomes a preview (`docs/PREVIEW.md`). Walking the list with `j` held
+    /// down must not open an attach per row it passes over.
+    pending_preview: Option<(Uuid, std::time::Instant)>,
+    /// When the pane last swapped what it previews. `None` until the first
+    /// one, which is why a highlight landing on a still sidebar shows at once.
+    last_preview_at: Option<std::time::Instant>,
+    /// Sessions attached only because they were previewed, oldest first. Kept
+    /// connected past the preview so stepping back onto a row is instant, and
+    /// bounded so a long walk doesn't leave a socket per session behind.
+    preview_lru: Vec<Uuid>,
+    /// Fingerprint of the last frame drawn. The loop compares a freshly
+    /// computed key against this and skips the repaint when they match — an
+    /// idle TUI used to emit a full diff 30 times a second forever, which over
+    /// a remote terminal is constant traffic for no change on screen.
+    last_frame: Option<FrameKey>,
+    /// When that frame went out, for the periodic refresh below.
+    last_drawn_at: std::time::Instant,
+    /// Bumped by every path that mutates `AppState` outside the catalog and
+    /// the attached pane: keys, mouse, draft results, link transitions. Those
+    /// mutations are too diffuse to fingerprint individually, so the loop
+    /// treats "an input was processed" as "assume the frame is stale".
+    epoch: u64,
 }
 
+/// Everything a frame is built from that is cheap to sample every tick.
+/// Equal keys mean an identical frame, so the repaint can be skipped.
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+struct FrameKey {
+    catalog: u64,
+    epoch: u64,
+    /// Active pane's session, its screen revision, and its link state.
+    pane: Option<(Uuid, u64, crate::session_task::SessionState)>,
+    area: ratatui::layout::Size,
+}
+
+/// Session cards carry a duration that advances on its own (`docs/SIDEBAR.md`),
+/// so a frame is never allowed to stand for longer than this even when nothing
+/// else changed.
+const CLOCK_REFRESH: Duration = Duration::from_secs(1);
+
+/// Shortest gap between two pane swaps (`docs/PREVIEW.md`). The first
+/// highlight to land shows at once; this only bounds how often the pane may
+/// follow after that, so a fast walk down the list attaches to the row it
+/// started on and the row it stopped on rather than every row between.
+const PREVIEW_GAP: Duration = Duration::from_millis(120);
+
+/// How many preview-only attaches to keep connected behind the current one.
+const PREVIEW_BUDGET: usize = 3;
+
 impl std::fmt::Debug for App {
     fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
         f.debug_struct("App")
@@ -170,13 +216,19 @@ impl App {
             last_sent_size: HashMap::new(),
             clicks: ClickTracker::default(),
             focused_session: None,
+            pending_preview: None,
+            last_preview_at: None,
+            preview_lru: Vec::new(),
+            last_frame: None,
+            last_drawn_at: std::time::Instant::now(),
+            epoch: 0,
         }
     }
 
     /// Drive the loop until the user quits. Consumes self.
-    pub async fn run(
+    pub async fn run<B: ratatui::backend::Backend>(
         mut self,
-        terminal: &mut Terminal<CrosstermBackend<Stdout>>,
+        terminal: &mut Terminal<B>,
     ) -> Result<(), TuiError> {
         if let Ok(info) = self.daemon.daemon_info().await {
             self.home_dir = info.home_dir;
@@ -184,7 +236,7 @@ impl App {
         let mut events = EventStream::new();
         loop {
             self.sync_focus().await;
-            self.redraw(terminal)?;
+            self.redraw_if_stale(terminal)?;
 
             tokio::select! {
                 Some(Ok(ev)) = events.next() => {
@@ -193,17 +245,24 @@ impl App {
                     }
                 }
                 Some(update) = self.draft_rx.recv() => {
+                    self.epoch = self.epoch.wrapping_add(1);
                     self.apply_draft_update(update).await;
                 }
                 _ = self.catalog.changed() => {
-                    // Render on next loop iteration.
+                    // Picked up by the frame key's catalog version.
                 }
                 _ = self.link.changed() => {
                     // The status indicator and the restart overlay both read
-                    // the link; redraw on the next loop iteration.
+                    // the link; neither is fingerprinted, so mark stale.
+                    self.epoch = self.epoch.wrapping_add(1);
                 }
                 _ = tokio::time::sleep(Duration::from_millis(33)) => {
-                    let effects = self.poll_due_probes_at(std::time::Instant::now());
+                    let now = std::time::Instant::now();
+                    let mut effects = self.poll_due_probes_at(now);
+                    effects.extend(self.poll_due_preview_at(now));
+                    if !effects.is_empty() {
+                        self.epoch = self.epoch.wrapping_add(1);
+                    }
                     self.perform(effects).await;
                 }
             }
@@ -217,6 +276,10 @@ impl App {
             return Ok(false);
         };
         let key = self.clicks.promote(key, std::time::Instant::now());
+        // Any key can move the cursor, open an overlay or edit a text buffer.
+        // Rather than fingerprint each of those, treat a processed input as
+        // proof the frame is stale.
+        self.epoch = self.epoch.wrapping_add(1);
 
         // The daemon is gone: everything a key could do goes through it, so
         // only the quit binding still resolves until it answers again.
@@ -253,16 +316,26 @@ impl App {
         match self.chord.feed(&key, &known) {
             ChordResult::Pending => Ok(false),
             ChordResult::Resolved(canon) => {
-                if let Some(act) = self.cfg.keymap.resolve(self.state.mode, &canon) {
-                    if matches!(act, Action::Quit) {
-                        return Ok(true);
+                let act = self.cfg.keymap.resolve(self.state.mode, &canon);
+                if matches!(act, Some(Action::Quit)) {
+                    return Ok(true);
+                }
+                let pty_owns_keys =
+                    self.state.mode == Mode::Insert && matches!(self.state.focus, Focus::Pane);
+                match act {
+                    // `Noop` suppresses a binding, and a key with no binding in
+                    // Insert mode is the session's — so a key bound to `Noop`
+                    // reaches the pty too. That is the escape hatch for taking
+                    // a default binding back.
+                    Some(Action::Noop) | None if pty_owns_keys => {
+                        let effects = self.forward_to_session(&key).into_iter().collect();
+                        self.perform(effects).await;
                     }
-                    let effects = self.dispatch(act);
-                    self.perform(effects).await;
-                } else if self.state.mode == Mode::Insert && matches!(self.state.focus, Focus::Pane)
-                {
-                    let effects = self.forward_to_session(&key).into_iter().collect();
-                    self.perform(effects).await;
+                    Some(act) => {
+                        let effects = self.dispatch(act);
+                        self.perform(effects).await;
+                    }
+                    None => {}
                 }
                 Ok(false)
             }
@@ -294,6 +367,7 @@ impl App {
                 self.state.sidebar_highlight = Some(SidebarItem::Session(id));
             }
         }
+        self.refresh_preview();
         true
     }
 
@@ -415,8 +489,15 @@ impl App {
                         if let Some(previous) = self.state.active_session() {
                             self.release_session(previous);
                         }
-                        effects.push(Effect::Attach(sid));
+                        // A previewed session is already attached: committing
+                        // to it keeps that stream rather than reopening one.
+                        if self.emulators.get(sid).is_none() {
+                            effects.push(Effect::Attach(sid));
+                        }
                     }
+                    // It is the pane's own session now, not a loan from the
+                    // preview budget.
+                    self.preview_lru.retain(|s| *s != sid);
                     self.state.attach_to_focused(sid);
                 }
             }
@@ -443,9 +524,96 @@ impl App {
                 }
             }
         }
+        // Every action can move the highlight or the focus, and the preview is
+        // a function of both (`docs/PREVIEW.md`).
+        self.refresh_preview();
         effects
     }
 
+    /// Recompute what the pane should be previewing. A session highlighted in
+    /// the sidebar is previewed as soon as [`PREVIEW_GAP`] has passed since the
+    /// last swap — immediately, for a highlight landing on a still list.
+    /// Anything else — a group row, the pane holding the keyboard, or the
+    /// highlight already sitting on the attached session — clears at once.
+    fn refresh_preview(&mut self) {
+        let wanted = match (self.state.focus, &self.state.sidebar_highlight) {
+            (Focus::Sidebar, Some(SidebarItem::Session(sid))) => Some(*sid),
+            _ => None,
+        };
+        match wanted {
+            Some(sid) if self.state.active_session() != Some(sid) => {
+                if self.state.preview != Some(sid) {
+                    let now = std::time::Instant::now();
+                    let due = match self.last_preview_at {
+                        Some(last) if now < last + PREVIEW_GAP => last + PREVIEW_GAP,
+                        _ => now,
+                    };
+                    self.pending_preview = Some((sid, due));
+                }
+            }
+            _ => {
+                self.pending_preview = None;
+                self.clear_preview();
+            }
+        }
+    }
+
+    /// The pane is free to follow: show the highlighted session, attaching it
+    /// if nothing already is.
+    fn poll_due_preview_at(&mut self, now: std::time::Instant) -> Vec<Effect> {
+        let Some((sid, due)) = self.pending_preview else {
+            return Vec::new();
+        };
+        if now < due {
+            return Vec::new();
+        }
+        self.pending_preview = None;
+        if self.state.preview == Some(sid) {
+            return Vec::new();
+        }
+        self.last_preview_at = Some(now);
+        self.state.preview = Some(sid);
+        // Set outside the input path, so nothing else marks the frame stale.
+        self.epoch = self.epoch.wrapping_add(1);
+        let fresh = self.emulators.get(sid).is_none();
+        if fresh {
+            self.preview_lru.retain(|s| *s != sid);
+            self.preview_lru.push(sid);
+        }
+        self.trim_preview_budget();
+        if fresh {
+            vec![Effect::Attach(sid)]
+        } else {
+            Vec::new()
+        }
+    }
+
+    fn clear_preview(&mut self) {
+        if self.state.preview.take().is_some() {
+            self.epoch = self.epoch.wrapping_add(1);
+        }
+        self.trim_preview_budget();
+    }
+
+    /// Drop preview-only attaches past the budget. What a tab holds, and what
+    /// is on screen right now, are never candidates.
+    fn trim_preview_budget(&mut self) {
+        while self.preview_lru.len() > PREVIEW_BUDGET {
+            let held: HashSet<Uuid> = self
+                .state
+                .tabs
+                .iter()
+                .filter_map(crate::state::Tab::session)
+                .chain(self.state.preview)
+                .collect();
+            let Some(pos) = self.preview_lru.iter().position(|sid| !held.contains(sid)) else {
+                break;
+            };
+            let victim = self.preview_lru.remove(pos);
+            self.release_session(victim);
+        }
+    }
+
     /// Open a stream for `sid` if one isn't already running.
     fn attach(&mut self, sid: Uuid) {
         if self.emulators.get(sid).is_some() {
@@ -959,9 +1127,46 @@ impl App {
         self.focused_session = wanted;
     }
 
-    fn redraw(
+    /// Sample everything a frame depends on. Cheap: two atomic loads, an
+    /// `RwLock` read of a `u64`, and the backend's size.
+    fn frame_key(&self, area: ratatui::layout::Size) -> FrameKey {
+        let pane = self.state.displayed_session().and_then(|sid| {
+            self.emulators
+                .get(sid)
+                .map(|h| (sid, h.revision(), h.state()))
+        });
+        FrameKey {
+            catalog: self.catalog.version(),
+            epoch: self.epoch,
+            pane,
+            area,
+        }
+    }
+
+    /// Repaint only when the frame key moved, or the clock refresh is due.
+    fn redraw_if_stale<B: ratatui::backend::Backend>(
         &mut self,
-        terminal: &mut Terminal<CrosstermBackend<Stdout>>,
+        terminal: &mut Terminal<B>,
+    ) -> Result<(), TuiError> {
+        // Polled rather than driven off `Event::Resize`: `Terminal::draw`'s own
+        // autoresize only runs on a draw, and a skipped draw must still notice
+        // the terminal changed shape.
+        let area = terminal
+            .size()
+            .map_err(|e| TuiError::Terminal(e.to_string()))?;
+        let key = self.frame_key(area);
+        if self.last_frame == Some(key) && self.last_drawn_at.elapsed() < CLOCK_REFRESH {
+            return Ok(());
+        }
+        self.redraw(terminal)?;
+        self.last_frame = Some(key);
+        self.last_drawn_at = std::time::Instant::now();
+        Ok(())
+    }
+
+    fn redraw<B: ratatui::backend::Backend>(
+        &mut self,
+        terminal: &mut Terminal<B>,
     ) -> Result<(), TuiError> {
         let snap = self.catalog.snapshot();
         let attached: HashSet<Uuid> = self
@@ -975,21 +1180,31 @@ impl App {
             highlight: self.state.sidebar_highlight.clone(),
             attached,
         };
-        let active_sid = self.state.active_session();
-        let pane = active_sid.and_then(|sid| {
+        let shown_sid = self.state.displayed_session();
+        let previewing = self.state.preview.is_some();
+        let pane = shown_sid.and_then(|sid| {
             self.emulators.get(sid).map(|h| Pane {
                 screen: h.screen.clone(),
                 status: PaneStatus::from(h.state()),
-                focused: matches!(self.state.focus, Focus::Pane),
+                // A preview never owns the keyboard, so it never draws a
+                // cursor either (`docs/PREVIEW.md`).
+                focused: matches!(self.state.focus, Focus::Pane) && !previewing,
             })
         });
-        let pane_title = match active_sid {
-            Some(sid) => snap
-                .sessions
-                .iter()
-                .find(|session| session.id == sid)
-                .map(crate::sidebar::name_for)
-                .unwrap_or_else(|| "session".into()),
+        let pane_title = match shown_sid {
+            Some(sid) => {
+                let name = snap
+                    .sessions
+                    .iter()
+                    .find(|session| session.id == sid)
+                    .map(crate::sidebar::name_for)
+                    .unwrap_or_else(|| "session".into());
+                if previewing {
+                    format!("{name}  ·  preview")
+                } else {
+                    name
+                }
+            }
             None => "session".into(),
         };
 
@@ -1017,7 +1232,7 @@ impl App {
         // Resize propagation: record the active pane's rect, recompute the
         // per-dimension min for every attached session, send Resize when
         // changed.
-        if let (Some(sid), Some(rect)) = (active_sid, self.region.pane) {
+        if let (Some(sid), Some(rect)) = (shown_sid, self.region.pane) {
             self.emulators.resize_tracker_mut().set_pane_size(
                 sid,
                 "active",
@@ -1257,6 +1472,100 @@ mod tests {
         )
     }
 
+    /// Counts how many times the loop actually repainted, by watching the
+    /// `TestBackend` buffer's generation via `draw` calls.
+    fn drew(app: &mut App, terminal: &mut Terminal<ratatui::backend::TestBackend>) -> bool {
+        let before = app.last_drawn_at;
+        app.redraw_if_stale(terminal).unwrap();
+        app.last_drawn_at != before
+    }
+
+    #[test]
+    fn unchanged_frame_is_not_repainted() {
+        let mut app = make_app();
+        let mut terminal = Terminal::new(ratatui::backend::TestBackend::new(80, 24)).unwrap();
+
+        assert!(drew(&mut app, &mut terminal), "first frame must paint");
+        assert!(
+            !drew(&mut app, &mut terminal),
+            "nothing changed; the repaint should be skipped"
+        );
+    }
+
+    #[test]
+    fn a_processed_key_makes_the_frame_stale() {
+        let mut app = make_app();
+        let mut terminal = Terminal::new(ratatui::backend::TestBackend::new(80, 24)).unwrap();
+        drew(&mut app, &mut terminal);
+
+        app.epoch = app.epoch.wrapping_add(1);
+        assert!(drew(&mut app, &mut terminal));
+    }
+
+    #[test]
+    fn a_catalog_event_makes_the_frame_stale() {
+        let mut app = make_app();
+        let mut terminal = Terminal::new(ratatui::backend::TestBackend::new(80, 24)).unwrap();
+        drew(&mut app, &mut terminal);
+
+        app.catalog
+            .apply_event(maestro_protocol::CatalogEvent::Snapshot {
+                sessions: Vec::new(),
+            });
+        assert!(drew(&mut app, &mut terminal));
+    }
+
+    #[test]
+    fn a_resize_makes_the_frame_stale() {
+        let mut app = make_app();
+        let mut terminal = Terminal::new(ratatui::backend::TestBackend::new(80, 24)).unwrap();
+        drew(&mut app, &mut terminal);
+
+        terminal.backend_mut().resize(120, 40);
+        assert!(drew(&mut app, &mut terminal));
+    }
+
+    #[test]
+    fn pane_output_makes_the_frame_stale() {
+        use crate::session_task::{SessionHandle, SessionState};
+        use std::sync::atomic::{AtomicU64, AtomicU8};
+        use std::sync::{Arc, Mutex};
+
+        let mut app = make_app();
+        let mut terminal = Terminal::new(ratatui::backend::TestBackend::new(80, 24)).unwrap();
+
+        let sid = Uuid::from_u128(7);
+        let revision = Arc::new(AtomicU64::new(0));
+        app.emulators.insert(
+            sid,
+            SessionHandle {
+                tx: tokio::sync::mpsc::channel(1).0,
+                screen: Arc::new(Mutex::new(vt100::Parser::new(24, 80, 0))),
+                state: Arc::new(AtomicU8::new(SessionState::Live as u8)),
+                revision: revision.clone(),
+            },
+        );
+        app.state.attach_to_focused(sid);
+        drew(&mut app, &mut terminal);
+        assert!(!drew(&mut app, &mut terminal), "idle pane must not repaint");
+
+        revision.fetch_add(1, std::sync::atomic::Ordering::Release);
+        assert!(drew(&mut app, &mut terminal), "new PTY bytes must repaint");
+    }
+
+    #[test]
+    fn a_stale_clock_repaints_even_with_no_events() {
+        let mut app = make_app();
+        let mut terminal = Terminal::new(ratatui::backend::TestBackend::new(80, 24)).unwrap();
+        drew(&mut app, &mut terminal);
+        assert!(!drew(&mut app, &mut terminal));
+
+        // Session cards show an advancing duration, so a frame may not stand
+        // for longer than CLOCK_REFRESH regardless of the key.
+        app.last_drawn_at = std::time::Instant::now() - CLOCK_REFRESH;
+        assert!(drew(&mut app, &mut terminal));
+    }
+
     #[test]
     fn enter_insert_then_leave() {
         let mut app = make_app();
@@ -1332,6 +1641,188 @@ mod tests {
         assert_eq!(app.state.overlay(), Some(&OverlayKind::Spawn));
     }
 
+    /// Seed the catalog with `ids` as sessions in one directory.
+    fn app_with_sessions(ids: &[Uuid]) -> App {
+        use chrono::Utc;
+        use maestro_protocol::{CatalogEvent, Session, SessionStatus};
+        let app = make_app();
+        app.catalog.apply_event(CatalogEvent::Snapshot {
+            sessions: ids
+                .iter()
+                .map(|id| Session {
+                    id: *id,
+                    command: "bash".into(),
+                    cwd: std::path::PathBuf::from("/"),
+                    env: Default::default(),
+                    metadata: Default::default(),
+                    worktree: None,
+                    status: SessionStatus::Running,
+                    created_at: Utc::now(),
+                    foreground: None,
+                    activity: Default::default(),
+                    activity_detail: None,
+                    last_activity_at: Utc::now(),
+                    activity_since: chrono::Utc::now(),
+                    current_cwd: None,
+                    blocked_work: None,
+                })
+                .collect(),
+        });
+        app
+    }
+
+    fn fake_handle() -> crate::session_task::SessionHandle {
+        use crate::session_task::{SessionHandle, SessionState};
+        use std::sync::atomic::{AtomicU64, AtomicU8};
+        use std::sync::{Arc, Mutex};
+        SessionHandle {
+            tx: tokio::sync::mpsc::channel(1).0,
+            screen: Arc::new(Mutex::new(vt100::Parser::new(24, 80, 0))),
+            state: Arc::new(AtomicU8::new(SessionState::Live as u8)),
+            revision: Arc::new(AtomicU64::new(0)),
+        }
+    }
+
+    fn after_gap() -> std::time::Instant {
+        std::time::Instant::now() + PREVIEW_GAP + Duration::from_millis(1)
+    }
+
+    /// docs/PREVIEW.md: the highlight shows a session in the pane without the
+    /// tab taking it on.
+    #[test]
+    fn highlighting_a_session_previews_it_without_waiting() {
+        let a = Uuid::from_u128(1);
+        let mut app = app_with_sessions(&[a]);
+        app.dispatch(Action::SidebarNext);
+
+        // The list was still, so the pane follows on the next poll — no gap to
+        // wait out first (docs/PREVIEW.md).
+        assert_eq!(
+            app.poll_due_preview_at(std::time::Instant::now()),
+            vec![Effect::Attach(a)]
+        );
+        assert_eq!(app.state.preview, Some(a));
+        assert_eq!(app.state.displayed_session(), Some(a));
+        // The tab is untouched — the preview is a view, not a layout change.
+        assert_eq!(app.state.active_tab().session(), None);
+    }
+
+    /// The gap only bounds the *second* swap, so a burst costs two mounts.
+    #[test]
+    fn a_second_move_inside_the_gap_waits_for_it() {
+        let a = Uuid::from_u128(1);
+        let b = Uuid::from_u128(2);
+        let mut app = app_with_sessions(&[a, b]);
+
+        app.dispatch(Action::SidebarNext);
+        let now = std::time::Instant::now();
+        assert_eq!(app.poll_due_preview_at(now), vec![Effect::Attach(a)]);
+
+        app.dispatch(Action::SidebarNext);
+        assert_eq!(app.poll_due_preview_at(now), vec![]);
+        assert_eq!(app.state.preview, Some(a));
+
+        assert_eq!(
+            app.poll_due_preview_at(after_gap()),
+            vec![Effect::Attach(b)]
+        );
+        assert_eq!(app.state.preview, Some(b));
+    }
+
+    /// A fast walk down the list attaches to where it stopped, not to every
+    /// row it crossed.
+    #[test]
+    fn walking_past_rows_only_previews_the_one_it_lands_on() {
+        let a = Uuid::from_u128(1);
+        let b = Uuid::from_u128(2);
+        let mut app = app_with_sessions(&[a, b]);
+        app.dispatch(Action::SidebarNext);
+        app.dispatch(Action::SidebarNext);
+
+        let effects = app.poll_due_preview_at(after_gap());
+        assert_eq!(effects, vec![Effect::Attach(b)]);
+        assert_eq!(app.state.preview, Some(b));
+    }
+
+    /// The pane's own session is not something to preview.
+    #[test]
+    fn highlighting_the_attached_session_clears_the_preview() {
+        let a = Uuid::from_u128(1);
+        let b = Uuid::from_u128(2);
+        let mut app = app_with_sessions(&[a, b]);
+        app.state.attach_to_focused(a);
+        app.state.focus = Focus::Sidebar;
+
+        app.state.sidebar_highlight = Some(SidebarItem::Session(b));
+        app.refresh_preview();
+        app.poll_due_preview_at(after_gap());
+        assert_eq!(app.state.preview, Some(b));
+
+        app.state.sidebar_highlight = Some(SidebarItem::Session(a));
+        app.refresh_preview();
+        assert_eq!(app.state.preview, None);
+        assert_eq!(app.state.displayed_session(), Some(a));
+    }
+
+    /// Moving off every session — onto a group row, or into the pane — puts
+    /// back what the tab was showing.
+    #[test]
+    fn leaving_the_session_rows_ends_the_preview() {
+        let a = Uuid::from_u128(1);
+        let b = Uuid::from_u128(2);
+        let mut app = app_with_sessions(&[a, b]);
+        app.state.attach_to_focused(a);
+        app.state.focus = Focus::Sidebar;
+        app.state.sidebar_highlight = Some(SidebarItem::Session(b));
+        app.refresh_preview();
+        app.poll_due_preview_at(after_gap());
+
+        app.dispatch(Action::FocusPane(crate::action::Direction::Right));
+        assert_eq!(app.state.preview, None);
+        assert_eq!(app.state.displayed_session(), Some(a));
+    }
+
+    /// Committing keeps the stream the preview already opened.
+    #[test]
+    fn attaching_to_a_previewed_session_reuses_its_stream() {
+        let a = Uuid::from_u128(1);
+        let mut app = app_with_sessions(&[a]);
+        app.dispatch(Action::SidebarNext);
+        app.poll_due_preview_at(after_gap());
+        // Stand in for the attach the effect would have opened.
+        app.emulators.insert(a, fake_handle());
+
+        let effects = app.dispatch(Action::AttachHighlighted);
+        assert_eq!(effects, vec![]);
+        assert_eq!(app.state.active_tab().session(), Some(a));
+        assert_eq!(app.state.preview, None);
+        // No longer on loan from the preview budget.
+        assert!(!app.preview_lru.contains(&a));
+    }
+
+    /// Preview-only attaches are kept for a step back, but bounded.
+    #[test]
+    fn preview_attaches_are_dropped_past_the_budget() {
+        let ids: Vec<Uuid> = (1..=(PREVIEW_BUDGET as u128 + 2))
+            .map(Uuid::from_u128)
+            .collect();
+        let mut app = app_with_sessions(&ids);
+        // Each row is previewed in its own gap window, so all of them land.
+        let mut clock = std::time::Instant::now();
+        for id in &ids {
+            app.state.sidebar_highlight = Some(SidebarItem::Session(*id));
+            app.refresh_preview();
+            clock += PREVIEW_GAP + Duration::from_millis(1);
+            app.poll_due_preview_at(clock);
+            app.emulators.insert(*id, fake_handle());
+        }
+
+        assert_eq!(app.preview_lru.len(), PREVIEW_BUDGET);
+        // The oldest rows previewed are gone; the newest are still warm.
+        assert!(app.emulators.get(ids[0]).is_none());
+        assert!(app.emulators.get(*ids.last().unwrap()).is_some());
+    }
+
     /// Seed the catalog with one session and highlight it.
     fn app_with_highlighted_session(sid: Uuid) -> App {
         use chrono::Utc;
@@ -2076,6 +2567,78 @@ mod tests {
         assert!(app.forward_to_session(&InputKey::Enter).is_none());
     }
 
+    /// Drive one key event through an app in Insert mode with a session
+    /// attached, and report the bytes that reached that session.
+    async fn bytes_sent_for(section: &TuiSection, ev: CtEvent) -> Option<Vec<u8>> {
+        use crate::session_task::{SessionHandle, SessionState};
+        use std::sync::atomic::{AtomicU64, AtomicU8};
+        use std::sync::{Arc, Mutex};
+        use tokio::sync::mpsc;
+
+        let sid = Uuid::from_u128(41);
+        let mut app = App::new(
+            TuiConfig::load(section).unwrap(),
+            CatalogStore::default(),
+            DaemonClient::new("http://127.0.0.1:7070"),
+            DaemonLink::default(),
+        );
+        let (tx, mut rx) = mpsc::channel(4);
+        app.emulators.insert(
+            sid,
+            SessionHandle {
+                tx,
+                screen: Arc::new(Mutex::new(vt100::Parser::new(24, 80, 0))),
+                state: Arc::new(AtomicU8::new(SessionState::Live as u8)),
+                revision: Arc::new(AtomicU64::new(0)),
+            },
+        );
+        app.state.attach_to_focused(sid);
+        app.state.mode = Mode::Insert;
+        app.state.focus = Focus::Pane;
+        app.handle_event(ev).await.unwrap();
+        match rx.try_recv() {
+            Ok(SessionInput::Bytes(bytes)) => Some(bytes),
+            _ => None,
+        }
+    }
+
+    fn key_event(code: crossterm::event::KeyCode, mods: crossterm::event::KeyModifiers) -> CtEvent {
+        CtEvent::Key(crossterm::event::KeyEvent::new(code, mods))
+    }
+
+    /// Escape belongs to the session: full-screen apps (vim, Claude Code) read
+    /// it constantly, so no Insert-mode default may swallow it. The leader is
+    /// the way back to the sidebar.
+    #[tokio::test]
+    async fn escape_reaches_the_attached_session() {
+        let sent = bytes_sent_for(
+            &TuiSection::default(),
+            key_event(
+                crossterm::event::KeyCode::Esc,
+                crossterm::event::KeyModifiers::NONE,
+            ),
+        )
+        .await;
+        assert_eq!(sent, Some(vec![0x1b]));
+    }
+
+    /// `Noop` suppresses a binding, and in Insert mode a key with no binding is
+    /// the session's — so binding a key to `Noop` hands it to the pty.
+    #[tokio::test]
+    async fn a_noop_insert_binding_forwards_the_key_to_the_session() {
+        let mut section = TuiSection::default();
+        section.keymap_insert.insert("ctrl-a".into(), "Noop".into());
+        let sent = bytes_sent_for(
+            &section,
+            key_event(
+                crossterm::event::KeyCode::Char('a'),
+                crossterm::event::KeyModifiers::CONTROL,
+            ),
+        )
+        .await;
+        assert_eq!(sent, Some(vec![0x01]));
+    }
+
     #[test]
     fn pane_scrollback_moves_and_user_input_returns_to_live_output() {
         use crate::session_task::{SessionHandle, SessionState};
@@ -2091,6 +2654,7 @@ mod tests {
             tx: mpsc::channel(1).0,
             screen: Arc::clone(&screen),
             state: Arc::new(AtomicU8::new(SessionState::Live as u8)),
+            revision: Arc::new(std::sync::atomic::AtomicU64::new(0)),
         };
         let mut app = make_app();
         app.state.active_tab_mut().pane = Some(sid);

crates/maestro-tui/src/catalog.rs

@@ -87,6 +87,16 @@ impl CatalogStore {
     }
 
     /// Cheap O(sessions) read of current state.
+    /// The version counter alone, without cloning the session list. The render
+    /// loop reads this every tick to decide whether the sidebar is stale.
+    pub fn version(&self) -> u64 {
+        self.inner
+            .state
+            .read()
+            .expect("catalog rwlock poisoned")
+            .version
+    }
+
     pub fn snapshot(&self) -> CatalogSnapshot {
         let s = self.inner.state.read().expect("catalog rwlock poisoned");
         let mut sessions: Vec<Session> = s.sessions.values().cloned().collect();

crates/maestro-tui/src/config.rs

@@ -52,10 +52,11 @@ const DEFAULT_NORMAL: &[(&str, &str)] = &[
     // because Normal mode only exists while the sidebar is focused, so
     // nothing forwards it to a pty.
     ("tab", "AttachHighlighted"),
-    ("s", "OpenSpawnModal"),
-    // Fast-forward spawn (#67): the spawn key's neighbour does the same
+    // `n`/`N`, the same pair the web client binds.
+    ("n", "OpenSpawnModal"),
+    // Fast-forward spawn (#67): the spawn key's shifted twin does the same
     // thing with every default resolved and no form.
-    ("S", "FastForwardSpawn"),
+    ("N", "FastForwardSpawn"),
     ("x", "KillHighlighted"),
     ("r", "RenameHighlighted"),
     // Focus
@@ -74,10 +75,13 @@ const DEFAULT_NORMAL: &[(&str, &str)] = &[
     ("mouse:dblclick(sidebar-row)", "AttachHighlighted"),
 ];
 
-/// Default Insert-mode bindings. The leader (`LeaveInsert`) is inserted
-/// dynamically by [`TuiConfig::load`] so rebinding it rebinds its Insert
-/// escape automatically; `esc` is a second, fixed way back to the sidebar.
-const DEFAULT_INSERT: &[(&str, &str)] = &[("esc", "LeaveInsert")];
+/// Default Insert-mode bindings — deliberately empty. Every key typed in
+/// Insert mode belongs to the session, `esc` included: full-screen apps read
+/// it constantly, so binding it here would make it unreachable. The only way
+/// back to the sidebar is the leader (`LeaveInsert`), which
+/// [`TuiConfig::load`] inserts dynamically so rebinding the leader rebinds
+/// the Insert escape with it.
+const DEFAULT_INSERT: &[(&str, &str)] = &[];
 
 impl TuiConfig {
     /// Build a runtime config from a [`TuiSection`] (typically the `tui`
@@ -220,18 +224,18 @@ mod tests {
             Some(Action::AttachHighlighted),
         );
         assert_eq!(
-            cfg.keymap.resolve(Mode::Normal, "s"),
+            cfg.keymap.resolve(Mode::Normal, "n"),
             Some(Action::OpenSpawnModal),
         );
         assert_eq!(
-            cfg.keymap.resolve(Mode::Normal, "S"),
+            cfg.keymap.resolve(Mode::Normal, "N"),
             Some(Action::FastForwardSpawn),
         );
     }
 
     /// AoE-style defaults (#shortcuts): `q` and `tab` are bare because Normal
     /// mode only exists while the sidebar is focused, so neither can leak
-    /// into a pty; `esc` is a second way out of Insert alongside the leader.
+    /// into a pty; `esc` stays unbound in Insert so it reaches the session.
     #[test]
     fn aoe_style_defaults_are_bound() {
         let cfg = TuiConfig::load(&TuiSection::default()).unwrap();
@@ -240,10 +244,7 @@ mod tests {
             cfg.keymap.resolve(Mode::Normal, "tab"),
             Some(Action::AttachHighlighted),
         );
-        assert_eq!(
-            cfg.keymap.resolve(Mode::Insert, "esc"),
-            Some(Action::LeaveInsert),
-        );
+        assert_eq!(cfg.keymap.resolve(Mode::Insert, "esc"), None);
     }
 
     #[test]
@@ -311,18 +312,18 @@ mod tests {
         assert!(s.contains("ctrl-glorb"), "diagnostic: {s}");
     }
 
-    /// Regression for #70: the previous canonical form of a real Shift+S
-    /// keypress was `"shift-S"`, which the default `"S"` binding never
+    /// Regression for #70: the previous canonical form of a real Shift+N
+    /// keypress was `"shift-N"`, which the default `"N"` binding never
     /// matched. Drive the actual crossterm event, not the binding string,
     /// so the dead-key bug can't come back unnoticed.
     #[test]
-    fn real_shift_s_keypress_resolves_to_fast_forward_spawn() {
+    fn real_shift_n_keypress_resolves_to_fast_forward_spawn() {
         use crossterm::event::{Event as CtEvent, KeyCode, KeyEvent, KeyModifiers};
 
         use crate::input::{canonicalise, Region};
 
         let cfg = TuiConfig::load(&TuiSection::default()).unwrap();
-        let ev = CtEvent::Key(KeyEvent::new(KeyCode::Char('S'), KeyModifiers::SHIFT));
+        let ev = CtEvent::Key(KeyEvent::new(KeyCode::Char('N'), KeyModifiers::SHIFT));
         let key = canonicalise(&ev, |_, _| Region::Unknown).expect("key event canonicalises");
 
         assert_eq!(

crates/maestro-tui/src/emulators.rs

@@ -168,6 +168,7 @@ mod tests {
             tx: mpsc::channel(1).0,
             screen: Arc::new(Mutex::new(vt100::Parser::new(24, 80, 0))),
             state: Arc::new(AtomicU8::new(SessionState::Live as u8)),
+            revision: Arc::new(std::sync::atomic::AtomicU64::new(0)),
         };
         emulators.insert(id, handle);
         assert!(emulators.get(id).is_some());

crates/maestro-tui/src/input.rs

@@ -597,7 +597,8 @@ mod tests {
     /// so a real Shift+S delivers `Char { c: 'S', shift: true }`. Its
     /// canonical form must be the bare `"S"` a keymap binds, not `"shift-S"` —
     /// the uppercase letter already says "shifted"; a redundant prefix would
-    /// make the default `S` binding unreachable from the keyboard (#70).
+    /// make every uppercase binding (the default `N`) unreachable from the
+    /// keyboard (#70).
     #[test]
     fn shift_flag_is_redundant_for_an_already_uppercase_char() {
         let k = InputKey::Char {

crates/maestro-tui/src/lib.rs

@@ -24,6 +24,7 @@ pub mod state;
 pub mod terminal;
 pub mod text_input;
 
+use std::io::BufWriter;
 use std::path::PathBuf;
 use std::time::Duration;
 
@@ -121,13 +122,23 @@ pub async fn run(cfg: RunConfig) -> Result<(), TuiError> {
     let _guard = terminal::TerminalGuard::enter().map_err(|e| match e {
         terminal::TerminalError::Io(io) => TuiError::Terminal(io.to_string()),
     })?;
-    let backend = CrosstermBackend::new(std::io::stdout());
+    // Buffered: ratatui issues one `write!` per cell run — thousands per
+    // frame — and an unbuffered `Stdout` takes the global stdout lock on every
+    // one of them. A single BufWriter collapses a frame into one flush.
+    let backend = CrosstermBackend::new(BufWriter::with_capacity(
+        FRAME_BUFFER_BYTES,
+        std::io::stdout(),
+    ));
     let mut terminal = Terminal::new(backend).map_err(|e| TuiError::Terminal(e.to_string()))?;
 
     let app = App::new(tui_cfg, catalog, daemon, link);
     app.run(&mut terminal).await
 }
 
+/// One full 200x50 repaint is ~5 KB of escape sequences; 64 KB leaves room for
+/// a large terminal without ever flushing mid-frame.
+const FRAME_BUFFER_BYTES: usize = 64 * 1024;
+
 /// Startup probe budget, applied to connect *and* the whole request: the user is
 /// staring at a terminal, so an unreachable daemon must fail in under a second.
 const HEALTH_TIMEOUT: Duration = Duration::from_millis(500);

crates/maestro-tui/src/session_task.rs

@@ -14,7 +14,7 @@
 //!   parser is **not** reset on reconnect — the last-known frame stays
 //!   visible until new bytes arrive, so the user doesn't see a blank.
 
-use std::sync::atomic::{AtomicU8, Ordering};
+use std::sync::atomic::{AtomicU64, AtomicU8, Ordering};
 use std::sync::{Arc, Mutex};
 use std::time::Duration;
 
@@ -56,11 +56,15 @@ pub enum SessionState {
 ///   here.
 /// - `state` — `Arc<AtomicU8>`: live status of the WS, queryable without
 ///   holding the screen lock.
+/// - `revision` — `Arc<AtomicU64>`: bumped every time the parser's screen is
+///   mutated. The render loop compares it against the last drawn frame's so an
+///   idle pane costs a `load` instead of a repaint.
 #[derive(Clone)]
 pub struct SessionHandle {
     pub tx: mpsc::Sender<SessionInput>,
     pub screen: Arc<Mutex<vt100::Parser>>,
     pub(crate) state: Arc<AtomicU8>,
+    pub(crate) revision: Arc<AtomicU64>,
 }
 
 impl std::fmt::Debug for SessionHandle {
@@ -81,6 +85,12 @@ impl SessionHandle {
         }
     }
 
+    /// Monotonic counter of screen mutations. Only equality across two reads
+    /// is meaningful — the loop uses it to decide whether a frame is stale.
+    pub fn revision(&self) -> u64 {
+        self.revision.load(Ordering::Acquire)
+    }
+
     /// Stop the underlying task. Used when the pane closes and the user has
     /// no other tabs pointing at this session.
     pub fn end(&self) {
@@ -109,9 +119,11 @@ impl SessionTask {
         let (tx, mut rx) = mpsc::channel::<SessionInput>(64);
         let parser = Arc::new(Mutex::new(vt100::Parser::new(rows, cols, SCROLLBACK_ROWS)));
         let state = Arc::new(AtomicU8::new(SessionState::Connecting as u8));
+        let revision = Arc::new(AtomicU64::new(0));
 
         let parser_bg = parser.clone();
         let state_bg = state.clone();
+        let revision_bg = revision.clone();
 
         tokio::spawn(async move {
             let url = ws_url;
@@ -151,6 +163,7 @@ impl SessionTask {
                                 }
                                 SessionInput::Resize { cols, rows } => {
                                     parser_bg.lock().expect("vt100 parser mutex").set_size(rows, cols);
+                                    revision_bg.fetch_add(1, Ordering::Release);
                                     let frame = serde_json::to_string(&ClientControl::Resize {
                                         cols,
                                         rows,
@@ -166,6 +179,7 @@ impl SessionTask {
                             match frame {
                                 Some(Ok(Message::Binary(bytes))) => {
                                     parser_bg.lock().expect("vt100 parser mutex").process(&bytes);
+                                    revision_bg.fetch_add(1, Ordering::Release);
                                 }
                                 Some(Ok(Message::Text(text))) => {
                                     // Ping/Pong control frames travel as text JSON. Reply to Ping.
@@ -202,6 +216,7 @@ impl SessionTask {
             tx,
             screen: parser,
             state,
+            revision,
         }
     }
 }
@@ -228,6 +243,7 @@ mod tests {
             tx: mpsc::channel(1).0,
             screen: Arc::new(Mutex::new(vt100::Parser::new(24, 80, 0))),
             state: Arc::new(AtomicU8::new(SessionState::Connecting as u8)),
+            revision: Arc::new(AtomicU64::new(0)),
         };
         assert_eq!(h.state(), SessionState::Connecting);
     }
@@ -238,8 +254,26 @@ mod tests {
             tx: mpsc::channel(1).0,
             screen: Arc::new(Mutex::new(vt100::Parser::new(24, 80, 0))),
             state: Arc::new(AtomicU8::new(SessionState::Live as u8)),
+            revision: Arc::new(AtomicU64::new(0)),
         };
         h.end();
         assert_eq!(h.state(), SessionState::Ended);
     }
+
+    #[test]
+    fn revision_starts_at_zero_and_tracks_screen_mutations() {
+        let revision = Arc::new(AtomicU64::new(0));
+        let h = SessionHandle {
+            tx: mpsc::channel(1).0,
+            screen: Arc::new(Mutex::new(vt100::Parser::new(24, 80, 0))),
+            state: Arc::new(AtomicU8::new(SessionState::Live as u8)),
+            revision: revision.clone(),
+        };
+        assert_eq!(h.revision(), 0);
+
+        // Stands in for the WS pump: process bytes, then bump.
+        h.screen.lock().unwrap().process(b"hello");
+        revision.fetch_add(1, Ordering::Release);
+        assert_eq!(h.revision(), 1);
+    }
 }

crates/maestro-tui/src/state.rs

@@ -63,6 +63,11 @@ pub struct AppState {
     pub mode: Mode,
     pub sidebar_visible: bool,
     pub sidebar_highlight: Option<SidebarItem>,
+    /// The session the pane is *previewing* (`docs/PREVIEW.md`): shown because
+    /// the sidebar highlight is on it, not because a tab holds it. It never
+    /// enters `tabs`, is never reported to the daemon as focused, and is
+    /// dropped the moment the highlight moves on.
+    pub preview: Option<Uuid>,
     /// Group paths whose cards are hidden. This is UI state rather than
     /// catalog state, so it survives every catalog redraw.
     pub collapsed_sidebar_groups: HashSet<PathBuf>,
@@ -91,6 +96,7 @@ impl AppState {
             mode: Mode::Normal,
             sidebar_visible: true,
             sidebar_highlight: None,
+            preview: None,
             collapsed_sidebar_groups: HashSet::new(),
             overlay: None,
         }
@@ -126,6 +132,9 @@ impl AppState {
     /// drop straight into Insert mode so keystrokes go to the session
     /// without an extra `i` press. The leader returns to Normal.
     pub fn attach_to_focused(&mut self, session_id: Uuid) {
+        // Committing to what was previewed: the pane owns it now, so the
+        // preview has nothing left to say.
+        self.preview = None;
         self.active_tab_mut().pane = Some(session_id);
         self.focus = Focus::Pane;
         self.mode = Mode::Insert;
@@ -150,6 +159,13 @@ impl AppState {
         self.active_tab().session()
     }
 
+    /// What the pane actually draws: the preview when one is up, otherwise the
+    /// active tab's session. A preview covers the pane without replacing it,
+    /// so ending one gives back exactly what was there (`docs/PREVIEW.md`).
+    pub fn displayed_session(&self) -> Option<Uuid> {
+        self.preview.or_else(|| self.active_session())
+    }
+
     /// Move the sidebar highlight one step through the rendered item
     /// sequence, in the direction of `delta` (positive = down), landing only
     /// on items `is_stop` accepts. Only the sign of `delta` matters. Wraps.

docs/COMMAND-BAR.md

@@ -0,0 +1,479 @@
+# COMMAND-BAR.md — the command bar contract
+
+One rule for the `ctrl-k` command bar in both clients, so the web bar and the
+TUI bar open the same way, rank the same results in the same order, and act on
+the same keys. Read this before changing either. Both clients implement exactly
+what is written here; if the behaviour needs to change, change it here first.
+
+The bar is one surface with three jobs: **go to a session**, **run a command**,
+**spawn into a directory**. It is not a new place to configure anything and it
+does not own any action — it chooses one and hands off to the flow that already
+implements it.
+
+## Opening
+
+`ctrl-k` opens the bar from anywhere:
+
+| Client | From | Notes |
+| --- | --- | --- |
+| TUI | Normal mode | Sidebar has the keyboard. |
+| TUI | Insert mode | The pane has the keyboard; the bar still opens. |
+| Web | Sidebar focused | Ordinary global binding. |
+| Web | Terminal focused | Intercepted before xterm sees it. |
+
+It is a **keymap entry like any other**, not a hard-wired key. In the TUI it is
+bound in both `DEFAULT_NORMAL` and `DEFAULT_INSERT` and is rebindable through
+`[tui.keymap.*]`; because the help overlay builds its lines from the live
+keymap, it appears there without a second list to maintain. In the web it is an
+entry in the command registry, so the `?` overlay lists it for the same reason.
+
+An attached xterm swallows every keystroke it is given, so the web binding is
+handled in the **capture phase**, ahead of the terminal — the same way the
+restart overlay swallows the app's shortcuts (`docs/RESTART.md`).
+
+### Escape hatch — sending a literal Ctrl-K
+
+Binding `ctrl-k` takes readline's kill-to-end-of-line away from every pane. The
+leader gives it back: **leader then `ctrl-k`** — `ctrl-a ctrl-k` by default —
+sends the literal `0x0B` byte to the focused pane and does not open the bar.
+
+The TUI already has a leader (`ctrl-a`, `[tui].leader`), and this chord goes
+through the existing chord resolution, so rebinding the leader rebinds the
+escape hatch with it — exactly as the leader's Insert-mode escape already
+works. **The web gains a leader for this**, defaulting to `ctrl-a` and
+mirroring the TUI's. `ctrl-a` is select-all in a browser; the web
+`preventDefault`s it, since selecting all of a terminal pane does nothing
+useful.
+
+Only Ctrl-K gets an escape hatch. No other control character is intercepted, so
+none of them needs one.
+
+### Focus round-trip
+
+Closing the bar returns the keyboard to whatever held it when the bar opened,
+the terminal included. A round trip through the bar never silently moves focus,
+and never counts as a focus change for the daemon: opening the bar does not
+report the pane unfocused, and closing it does not report a new focus. The bar
+is a view over the app, not a place in it.
+
+Opening the bar while a session is previewed (`docs/PREVIEW.md`) discards the
+preview first, like any other real change; the bar is not previewed into.
+
+## Structure
+
+The bar is a query line over a result list. By default the list is **flat and
+mixed** — sessions and commands ranked together — and rendered under **kind
+headers**: a header row naming the kind, then that kind's results.
+
+Grouping is a rendering of the ranking, never a reordering of it:
+
+- Results are ranked as one list by the algorithm below.
+- A kind's group holds its matches in that rank order.
+- **Groups are ordered by their best-scoring member.** The first row under the
+  first header is therefore the globally best result, and the highlight starts
+  on it.
+
+Two sigils, typed as the **first character** of the query, narrow the list to
+one kind:
+
+| Sigil | Kind | Candidates | Enter |
+| --- | --- | --- | --- |
+| `>` | commands | Every entry in the client's command registry — the web registry from the `?` overlay, the TUI's live `(chord, Action)` keymap for the current mode. | Runs the command. |
+| `~` | directories | Recent dirs (`GET /api/recent-dirs`) and the project list the spawn form already uses, with `GET /api/dirs` filling in as a path is typed. | Spawns a session there with every default resolved. |
+
+While a sigil is in force there is one kind, so the kind header is dropped. A
+command row shows its **key chord** beside its label, so the bar teaches the
+keymap instead of replacing it. A `~` spawn takes the same fast-forward path as
+`N` / `FastForwardSpawn`: an unresolvable default opens the pre-filled spawn
+form rather than failing silently.
+
+**Backspacing past a sigil returns to the mixed list.** The sigil is one
+character of the query like any other — deleting it is not a special key, it is
+the query becoming empty again.
+
+The sigil is only a sigil in first position. `>` or `~` typed anywhere else is
+a literal query character (a directory query is where a `~` is most likely to
+be typed twice, and the second one must reach the matcher).
+
+## Empty query
+
+With no sigil and an empty query the bar lists **sessions only, most recently
+focused first**, so `ctrl-k enter` is "back to where I just was". Commands and
+directories need a sigil or a query to appear; an empty bar is a session
+switcher.
+
+**Recency comes from the daemon**, not from client state — the same order in
+every client, on every device, including one that just loaded the page. The
+daemon stamps a last-focused time per session and ships it on the session like
+any other field (#145). Both of the ways focus moves stamp the same field: a
+client opening `/api/attach/:id`, and a client reporting focus explicitly at
+`POST /api/sessions/:id/focus` when it refocuses a pane that is already open.
+
+**A session that has never been focused sorts after every session that has**,
+and among those, most recently created first. Dead sessions sort after live
+ones regardless of recency: a session you cannot attach to is not where you
+just were.
+
+Under `>` an empty query lists every command in registry order. Under `~` it
+lists recent dirs, most recent first, then the project list.
+
+## Keys
+
+| Key | Action |
+| --- | --- |
+| `enter` | Open the highlighted result — attach the session, run the command, spawn into the directory. |
+| `tab` | Drill into the highlighted **session**'s action page. No effect on any other kind. |
+| `esc` | At the top level, close the bar. On an action page, return to the result list. |
+| `backspace` | Ordinary editing; at an empty query on an action page, return to the result list. |
+| `up` / `down` | Move the highlight. |
+| `ctrl-p` / `ctrl-n` | Move the highlight. |
+
+The highlight does not wrap: it stops at the first and last row. Kind headers
+are never landed on — they are labels, not rows.
+
+Enter on a session goes through the **same open path** the sidebar's click and
+the hash router already share, so a bar attach can never leave the layout in a
+state a click could not produce.
+
+### Drill-in — the session action page
+
+`tab` on a highlighted session opens that session's action page inside the same
+overlay: **kill**, **rename**, **spawn similar**. The page is still fuzzy
+searchable — the query line keeps working, now over those actions.
+
+- The overlay names the session being acted on, so the target is never
+  ambiguous.
+- Escape, or backspace at an empty query, returns to the result list **with the
+  previous query intact**. Drilling in and backing out is free.
+- Each action raises the flow it already has: kill goes through the existing
+  confirm-and-blockers dialog (`docs/WORKTREES.md`), rename through the
+  existing prompt pre-filled with the session's own name
+  (`docs/SIDEBAR.md`), spawn similar through the spawn form seeded from the
+  session's directory and command. The bar picks the action; it never
+  reimplements one.
+
+No actions beyond those three, and no action across more than one session.
+
+## Touch entry
+
+On the web, **tapping or focusing the sidebar's search field opens the bar**
+with an empty query. There is no `ctrl-k` on a phone and the product is
+mobile-first, so the field the operator already reaches for is the entry point.
+
+This **replaces** the sidebar's inline substring filter — one search affordance
+in the header, not two beside each other. The tree's "No matches" empty state
+belonged to that filter and goes with it; the bar's own no-results state takes
+over (see the fixture `F4`).
+
+At phone width the bar follows the bottom-sheet treatment the spawn modal
+already uses below 600px. Visuals otherwise come from `DESIGN.md`'s existing
+overlay tokens — the bar is the same family of surface as the spawn modal and
+the help overlay, not a new one.
+
+## What a candidate is
+
+The matcher is a pure function: `(query, candidates) → ranked subset with
+matched ranges`. It knows nothing about sessions, panes or the network. A
+candidate is a **kind** plus a set of **named text fields**, each with a fixed
+weight.
+
+| Kind | Field | Weight | Text |
+| --- | --- | --- | --- |
+| session | `name` | `0` | The name as the sidebar shows it: `metadata.name` if set, else the command line (`docs/SIDEBAR.md`'s fallback). |
+| session | `directory` | `-24` | The directory the sidebar groups it under, abbreviated: `~/dev/api`, not `/home/me/dev/api`. |
+| session | `command` | `-32` | The full command line, arguments included. |
+| session | `tool` | `-40` | The tool id the card's icon stands for (`claude`, `codex`, `opencode`, …), absent when the program is not one we have a mark for. |
+| command | `label` | `0` | The plain-language label — the web registry's label, the TUI's `Action::help_label`. |
+| directory | `path` | `0` | The path as displayed, abbreviated the same way. |
+
+A command's **key chord is displayed, not matched**. It is there to teach the
+keymap; matching it would make `>` results depend on a user's rebinds, and the
+two clients do not share a keymap.
+
+A candidate **matches** if at least one of its fields matches. Its score is the
+**best** `field score + field weight` across its fields, and the matched ranges
+it returns are those of that winning field — so a session found through its
+directory highlights inside the directory, not inside its name.
+
+## Match and rank
+
+Two independent implementations (#146 in TypeScript, #147 in Rust) must produce
+the same order for the same input. Everything below is exact.
+
+### Normalization
+
+- **Query**: lowercase, then remove every whitespace character. The result is
+  the *normalized query*. If it is empty, see "Empty query" below.
+- **Field text**: matched against its lowercased form. Bonuses are computed
+  against the **original** text, because case is a signal (`camelCase`) that
+  lowercasing destroys.
+- **Compact form** of a string: lowercase with whitespace removed. Used only
+  for the exact and prefix tests.
+
+Lowercasing is per-character simple lowercase (`char::to_lowercase` /
+`String.prototype.toLowerCase`). Positions are **character** positions —
+Unicode scalar values in Rust, UTF-16 code units in TypeScript, which agree for
+every character these fields realistically hold; ranges are returned in the
+host language's own unit, since they exist to slice that language's string.
+
+### What a match is
+
+Case-insensitive **subsequence**: every character of the normalized query
+appears in the lowercased field text, in order, not necessarily adjacent. A
+field with no such embedding does not match.
+
+### Word boundaries
+
+A matched character at position `p` earns exactly one character bonus, taking
+the first rule that applies:
+
+| Rule | Bonus |
+| --- | --- |
+| `p == 0` — first character of the field | `+18` |
+| The character before it is a **separator**: `/` `\` `-` `_` `.` `:` or a space | `+16` |
+| It is uppercase and the character before it is lowercase (a camelCase hump) | `+12` |
+| It is a digit and the character before it is not | `+12` |
+| Otherwise | `0` |
+
+That is one rule for both shapes the doc has to cover. In a **path**, `/` is a
+separator, so the first character of every segment is a word start: `foo` in
+`~/dev/foobar` starts a segment and outscores `foo` in `~/src/myfoo`, which
+starts nothing. In a **session name**, `-`, `_`, `.` and spaces do the same
+work, so `ws` reaches `web-search` more cheaply than `websearch`.
+
+### Score
+
+Let the query characters be matched at positions `p₀ < p₁ < … < pₘ₋₁`, and let
+`p₋₁ = -1`. For each matched character `i`, with `gap = pᵢ - pᵢ₋₁ - 1`:
+
+```
+contribution(i) = 16                      // every matched character
+                + bonus(pᵢ)               // the table above
+                + (gap == 0 ? +8          // adjacent to the previous match
+                            : -min(gap, 12))
+```
+
+`gap` for `i = 0` is the number of characters skipped before the first match, so
+a match that starts late is penalised exactly like an internal gap, and the cap
+is the same one.
+
+The **field score** is the sum of the contributions, plus at most one whole-field
+adjustment:
+
+- compact field text **equals** the normalized query → `+64`
+- else compact field text **starts with** the normalized query → `+32`
+
+Length is deliberately not in the score — it is a tie-break, so a long field
+never loses to a short one that matched worse.
+
+### Which embedding
+
+A query can sit in a field many ways. The one that counts is the
+**highest-scoring** embedding; among embeddings that score the same, the
+**leftmost** — compare position vectors element by element, smaller wins.
+
+Greedy leftmost-first matching is not sufficient and must not be used: in
+`maestro-tui`, `mtu` greedily takes `m₀ a₁ …` and never reaches `tui`. Both
+implementations use the obvious dynamic program over
+`(query index, text position)`, carrying the best score and its position
+vector, since the gap term depends only on the previous matched position.
+
+The whole-field adjustment is constant for a `(query, field)` pair, so adding it
+after the dynamic program cannot change which embedding wins.
+
+### Ordering
+
+Sort by score, highest first. Equal scores break in this order:
+
+1. **Kind** — `session`, then `command`, then `directory`.
+2. **Length of the matched field text**, shorter first.
+3. **The matched field text**, ascending, compared by code point, case
+   sensitive.
+4. **Input order.** The sort is stable, so candidates the caller ordered
+   deliberately — sessions most recently focused first, commands in registry
+   order — keep that order when nothing else separates them.
+
+Kind leads because that is the ruling the ambiguous cases need: a session named
+`kill` and the `kill` command that score alike put the session first, because
+the operator who typed a session's name meant the session.
+
+### Empty query
+
+A normalized query that is empty **matches every candidate**, each with score
+`0` and no ranges, in input order. The bar's own rules decide what is in the
+candidate list at that point (sessions only at the top level); the matcher does
+not filter by kind.
+
+## Fixtures
+
+These are the contract. Both matchers are tested against exactly these cases;
+the prose above is the explanation of why they come out this way.
+
+Candidates are written as `kind(fields)`; unlisted fields are absent.
+`session(name, dir, command, tool)`. Scores are shown for diagnosis — **the
+order is what is being asserted**, and an implementation that ranks correctly
+with different absolute numbers has still failed, because the numbers are how
+the next fixture stays predictable.
+
+### F1 — empty query keeps input order
+
+```
+query:      ""
+candidates: session("kill", "~/dev/api", "bash")
+            session("killer-app", "~/dev/killer-app", "claude --resume", "claude")
+            command("Kill selected session")
+expected:   session("kill")           score 0
+            session("killer-app")     score 0
+            command("Kill selected session")  score 0
+```
+
+Every candidate matches, in the order given. No ranges.
+
+### F2 — a session named `kill` against the `kill` command
+
+```
+query:      "kill"
+candidates: (as F1)
+expected:   session("kill")                   178   name
+            session("killer-app")             146   name
+            command("Kill selected session")  146   label
+```
+
+`kill` wins on the exact bonus. The other two **tie at 146** — both are a
+contiguous prefix match — and the kind tie-break puts the session first.
+
+### F3 — a fragment matching mid-segment inside a path
+
+```
+query:      "foo"
+candidates: directory("~/dev/foobar")
+            directory("~/src/myfoo")
+            directory("~/foo")
+expected:   directory("~/foo")         78   ranges [2,3,4]
+            directory("~/dev/foobar")  74   ranges [6,7,8]
+            directory("~/src/myfoo")   56   ranges [8,9,10]
+```
+
+The first two start a path segment; the third is mid-segment and loses by the
+whole boundary bonus. `~/foo` beats `~/dev/foobar` only because less was
+skipped before the match.
+
+### F4 — a query matching nothing
+
+```
+query:      "zzz"
+candidates: session("kill", "~/dev/api", "bash")
+            command("Kill selected session")
+expected:   (empty)
+```
+
+The matcher returns an empty list, never a list of zero-scored candidates. The
+bar renders its no-results state.
+
+### F5 — a non-contiguous subsequence
+
+```
+query:      "mtu"
+candidates: session("maestro-tui")
+            session("maestro-daemon")
+            session("mtui-scratch")
+expected:   session("mtui-scratch")  122   ranges [0,1,2]
+            session("maestro-tui")    91   ranges [0,8,9]
+```
+
+`maestro-daemon` has no `u` after its `t` and does not match. `maestro-tui`
+does, across a gap — which greedy matching would miss entirely.
+
+### F6 — a name beats a directory
+
+```
+query:      "api"
+candidates: session("api", "~/dev/web", "bash")
+            session("worker", "~/dev/api", "bash")
+expected:   session("api")     154   name
+            session("worker")   50   directory
+```
+
+The second session is found through its directory, and highlights there.
+
+### F7 — case-insensitive, tie broken by length
+
+```
+query:      "api"
+candidates: session("API-Gateway")
+            session("apiary")
+expected:   session("apiary")       122   name
+            session("API-Gateway")  122   name
+```
+
+Both are prefix matches and score identically. Same kind, so length decides:
+6 characters before 11. Input order does not save `API-Gateway`.
+
+### F8 — the tool field
+
+```
+query:      "claude"
+candidates: session("nameless", "~/dev/x", "claude --resume", "claude")
+            session("clay", "~/dev/y", "bash")
+expected:   session("nameless")  186   tool
+```
+
+`clay` has no `claude` subsequence anywhere and drops out. `nameless` matches
+its `tool` exactly (`+64`, weight `-40`, giving 186) which beats the prefix
+match on its `command` field (`+32`, weight `-32`, giving 162).
+
+### F9 — a word boundary inside a session name
+
+```
+query:      "ws"
+candidates: session("websearch")
+            session("web-search")
+expected:   session("web-search")  71   ranges [0,4]
+            session("websearch")   56   ranges [0,3]
+```
+
+The `s` after `-` earns the boundary bonus; the `s` inside `websearch` earns
+nothing.
+
+### F10 — command labels
+
+```
+query:      "se"
+candidates: command("Kill selected session")
+            command("Create a session")
+            command("Show help")
+expected:   command("Show help")             53   ranges [0,6]
+            command("Kill selected session") 51   ranges [5,6]
+            command("Create a session")      47   ranges [9,10]
+```
+
+`Show help` starts at position 0; the other two start at a word boundary but
+later, and pay for the skipped characters.
+
+### F11 — a query against session directories
+
+```
+query:      "dev"
+candidates: session("api", "~/dev/api", "bash")
+            session("notes", "~/documents/dev-notes", "nvim")
+            session("scratch", "~/srv/devops", "bash")
+expected:   session("api")      54   directory, ranges [2,3,4]
+            session("scratch")  50   directory, ranges [6,7,8]
+            session("notes")    44   directory, ranges [12,13,14]
+```
+
+All three start a path segment. They separate purely on how much was skipped
+first, and `notes` hits the `-12` gap cap.
+
+### F12 — exact beats prefix
+
+```
+query:      "quit"
+candidates: command("Quit Maestro")
+            command("Quit")
+expected:   command("Quit")           178   label
+            command("Quit Maestro")   146   label
+```
+
+The 32-point difference between the exact and prefix adjustments is the whole
+gap; nothing else about the two matches differs.

docs/INSTALL.md

@@ -141,7 +141,8 @@ chord_timeout_ms = 1000      # how long to hold a partial chord like `ctrl-w`
 
 [tui.keymap.normal]
 "i"            = "EnterInsert"
-"s"            = "OpenSpawnModal"
+"n"            = "OpenSpawnModal"
+"N"            = "FastForwardSpawn"
 "x"            = "KillHighlighted"
 "r"            = "RenameHighlighted"
 "?"            = "ShowHelp"

docs/PREVIEW.md

@@ -0,0 +1,75 @@
+# PREVIEW.md — the sidebar preview contract
+
+One rule for what the content pane shows while the operator is only moving
+around the sidebar, so the web client and the TUI behave the same. Read this
+before changing either. If the behaviour needs to change, change it here first.
+
+## The rule
+
+Highlighting a session in the sidebar shows that session in the content pane,
+as if it were focused, **without focusing it and without changing the layout**.
+Moving the highlight elsewhere puts back exactly what was on screen before.
+
+A preview is a view, not a state. Nothing about it is durable:
+
+- The layout is byte-for-byte identical before the preview and after it ends.
+- Nothing is persisted while a preview is up (the web client's layout is saved
+  to `localStorage`; a preview never reaches it).
+- The daemon is never told the previewed pane is focused, so a preview never
+  clears a session's `AwaitingInput` glow (`docs/SIDEBAR.md`).
+- The keyboard stays in the sidebar: the previewed terminal is on screen but
+  does not take focus, so the next `j`/`k` still walks the list.
+
+## Where the preview is shown
+
+| The previewed session is… | What happens |
+|---|---|
+| Already in a pane, in the active tab | That pane comes forward (its tab's focus moves to it). |
+| Already in a pane, in another tab | That tab is brought forward. The active tab is restored when the preview ends. |
+| Not in any pane | A throwaway tab carries it. It is removed when the preview ends. |
+
+The throwaway tab never counts as an open session: the tab bar does not appear
+because of it, the mobile shell does not switch away from the session list for
+it, and the sidebar does not mark the session as open.
+
+## What ends a preview
+
+- The highlight moves to another session — that session is previewed instead.
+- The highlight leaves every session (a folder row, or the list losing the
+  keyboard, or the pointer leaving the list): the previous view comes back.
+- Any real layout change (split, close, new tab, tab switch, drag): the preview
+  is discarded first, so a throwaway tab is never baked into the arrangement.
+
+## What commits a preview
+
+Choosing the previewed session — clicking or pressing Enter on its row,
+clicking into its pane, or handing the keyboard to the pane (web: `Tab` from
+the list; TUI: the attach binding) — keeps exactly what is on screen. A
+throwaway tab becomes a real one; a focus move inside an existing tab stands.
+Nothing moves a second time on commit.
+
+## Timing
+
+**A preview is never delayed.** Landing on a row — by pointer or by `j`/`k` —
+shows it on the next frame, and so does leaving every row. There is no
+settling period in front of the first preview, because that period would sit
+in front of the one preview the operator actually meant.
+
+What is bounded is how *often* the pane may swap: at most once per 120 ms.
+A burst inside one window — `j` held down, or the pointer sweeping the length
+of the sidebar — shows the row it started on, then the row it ended on, and
+none of the rows in between. So a walk costs a couple of pane mounts rather
+than one per row, without the operator ever waiting on one.
+
+The highlight itself is not bounded by any of this: the row lights up on the
+same frame as the input, whatever the pane behind it is doing.
+
+Touch has no hover, and a tap already opens a session, so touch never previews.
+
+## Cost
+
+A previewed session that no pane holds needs a live attach. Both clients keep
+it connected after the preview ends — the web client parks it in the connection
+pool's LRU, the TUI keeps its emulator until it falls out of the preview
+budget — so stepping back onto a row is instant rather than re-fetching
+scrollback.

docs/SIDEBAR.md

@@ -234,7 +234,7 @@ the agent, and answering 204 would hide it.
 
 A session's pane — the pane a client's own attach view is showing, never a
 sidebar highlight — clears its `AwaitingInput` glow once it has been
-**continuously focused for 5 seconds**: the operator has looked, so the rail
+**continuously focused for 1 second**: the operator has looked, so the rail
 stops asking for attention and the card reads as `Idle` instead. This is a
 real state change, not a client-side paint-over — the daemon computes it, so
 every client watching the session (web, TUI, a second pane on the same
@@ -274,3 +274,21 @@ than jumping to the end of the list.
 The web client needs a chord to reach the list at all (`Ctrl+Shift+H`, and the
 same chord back): an attached terminal owns every plain keystroke. The TUI uses
 `ctrl-w h`.
+
+Everything else is the same key on both clients:
+
+| key     | action                                      |
+|---------|---------------------------------------------|
+| `j`/`k` | move the highlight (arrows too)             |
+| `Enter` | open the session, or expand the folder      |
+| `Tab`   | hand the keyboard to the pane               |
+| `c`     | collapse or expand the highlighted folder   |
+| `r`     | rename the highlighted session              |
+| `x`     | kill the highlighted session                |
+| `n`     | open the spawn form                         |
+| `N`     | spawn with every default resolved           |
+| `?`     | show the shortcut overlay                   |
+
+The TUI binds these through its keymap, so a user can rebind any of them; the
+web client's are fixed. A binding added to one client belongs in this table and
+in both help overlays.

flake.nix

@@ -148,7 +148,7 @@
             pnpmDeps = (pkgs.fetchPnpmDeps.override { pnpm = pkgs.pnpm_10; }) {
               inherit (finalAttrs) pname version src;
               fetcherVersion = 3;
-              hash = "sha256-AvIrpXipbcp7hRujh/L4UAc6tAJOxe67P/iji6L/oL0=";
+              hash = "sha256-hOqiAbnjKsoQnV8lgto5HspDsLIb+48sNLkShIjCZPQ=";
             };
 
             buildPhase = ''
@@ -218,8 +218,8 @@
             settings = {
               # `nix run .#dev` works from a bare shell, not only from inside
               # `nix develop`, so the toolchain is put on PATH here rather than
-              # inherited. `/usr/bin:/bin` stays last for anything else a
-              # spawned session reaches for.
+              # inherited. This covers the build and Vite; the daemon widens it
+              # further for the sessions it spawns (see `daemon.command`).
               environment = [
                 "PATH=${lib.makeBinPath devTools}:/usr/bin:/bin"
                 # Not :7070: that is the daemon's own default, and the dev
@@ -241,7 +241,17 @@
                   # `environment`. A tmux socket of its own keeps dev sessions
                   # out of — and safe from — the tmux server belonging to
                   # whatever daemon the developer actually runs.
+                  #
+                  # A spawned session inherits the daemon's PATH, and the
+                  # toolchain PATH above holds build tools only — on NixOS the
+                  # trailing `/usr/bin:/bin` is all but empty, so every session
+                  # opened from the dev UI came up unable to find `claude`,
+                  # `zsh` or anything else the developer actually has. Append
+                  # the usual user profile directories so dev sessions behave
+                  # like real ones. Resolved by the shell at run time; the ones
+                  # that do not exist on a given host cost nothing.
                   command = ''
+                    PATH="$PATH:$HOME/.nix-profile/bin:/etc/profiles/per-user/$(id -un)/bin:/run/current-system/sw/bin:/usr/local/bin" \
                     MAESTRO_DAEMON_TMUX_TMPDIR="$PWD/.dev/tmux" \
                     RUST_LOG="''${RUST_LOG:-maestro=debug,info}" \
                       target/debug/maestro daemon

web/package.json

@@ -15,6 +15,7 @@
   "dependencies": {
     "@fontsource/jetbrains-mono": "^5.3.0",
     "@xterm/addon-fit": "^0.10.0",
+    "@xterm/addon-webgl": "^0.19.0",
     "@xterm/xterm": "^5.5.0"
   },
   "devDependencies": {

web/pnpm-lock.yaml

@@ -14,6 +14,9 @@ importers:
       '@xterm/addon-fit':
         specifier: ^0.10.0
         version: 0.10.0(@xterm/xterm@5.5.0)
+      '@xterm/addon-webgl':
+        specifier: ^0.19.0
+        version: 0.19.0
       '@xterm/xterm':
         specifier: ^5.5.0
         version: 5.5.0
@@ -348,6 +351,9 @@ packages:
     peerDependencies:
       '@xterm/xterm': ^5.0.0
 
+  '@xterm/addon-webgl@0.19.0':
+    resolution: {integrity: sha512-b3fMOsyLVuCeNJWxolACEUED0vm7qC0cy4wRvf3oURSzDTYVQiGPhTnhWZwIHdvC48Y+oLhvYXnY4XDXPoJo6A==}
+
   '@xterm/xterm@5.5.0':
     resolution: {integrity: sha512-hqJHYaQb5OptNunnyAnkHyM8aCjZ1MEIDTQu1iIbbTD/xops91NB5yq1ZK/dC2JDbVWtF23zUtl9JE2NqwT87A==}
 
@@ -772,6 +778,8 @@ snapshots:
     dependencies:
       '@xterm/xterm': 5.5.0
 
+  '@xterm/addon-webgl@0.19.0': {}
+
   '@xterm/xterm@5.5.0': {}
 
   assertion-error@2.0.1: {}

web/src/attach.ts

@@ -1,15 +1,31 @@
 import { FitAddon } from "@xterm/addon-fit";
+import { WebglAddon } from "@xterm/addon-webgl";
 import { Terminal } from "@xterm/xterm";
 import "@xterm/xterm/css/xterm.css";
 
 import { attachWsUrl } from "./routes.js";
 import { FOCUS_SIDEBAR_EVENT } from "./catalog.js";
+import { CommandSet, defineCommands } from "./commands.js";
 import { escapeHtml } from "./html.js";
 import { INITIAL_RECONNECT_MS, MAX_RECONNECT_MS } from "./reconnect.js";
 import { applyModsToChar, cursorSeq, tildeSeq } from "./keys.js";
 import { requestToggleDrawer } from "./drawer.js";
 import { splitCommand, toolIconSvg } from "./toolIcon.js";
 import type { ClientControl, Uuid } from "./types.js";
+import { WebglPolicy } from "./webglRenderer.js";
+
+// The pane's half of the command registry (#148): plain Escape hands the
+// keyboard back to the session list, the pair to the list's Tab.
+const paneKeys = new CommandSet(
+  defineCommands({
+    "pane.focusList": () => document.dispatchEvent(new CustomEvent(FOCUS_SIDEBAR_EVENT)),
+  }),
+  { preventDefault: false },
+);
+
+/** One budget for the whole page — see webglRenderer.ts for why contexts are
+ *  rationed rather than handed to every connection. */
+const webglPolicy = new WebglPolicy();
 
 /**
  * A single live attach: an xterm terminal bound to the daemon's attach WebSocket.
@@ -26,8 +42,10 @@ export interface AttachConnection {
   readonly sessionId: Uuid;
   /** The `.attach` element (header + terminal body) to mount into a pane. */
   readonly el: HTMLElement;
-  /** Becomes the visible view: fit to the pane, focus, sync size. */
-  onMount(): void;
+  /** Becomes the visible view: fit to the pane, focus, sync size.
+   *  `focus: false` mounts without taking the keyboard — what a sidebar
+   *  preview needs, so j/k keeps working while the pane is on screen. */
+  onMount(opts?: { focus?: boolean }): void;
   /** Parked into the cache: keep streaming, just stop driving focus/resize. */
   onUnmount(): void;
   /** Put the keyboard back into this terminal — what leaving the sidebar does. */
@@ -48,8 +66,6 @@ export interface AttachOptions {
   shouldReconnect?: (sessionId: Uuid, code: number) => boolean;
 }
 
-
-
 /** What the header shows about the session (name / command). Optional — falls
  * back to a short session id when the session isn't known yet. */
 export interface AttachInfo {
@@ -135,13 +151,79 @@ export function createAttachConnection(
   term.loadAddon(fit);
   term.open(body);
 
+  // GPU rendering is scoped to the mounted view, not the connection: acquired
+  // in onMount, released in onUnmount. See webglRenderer.ts.
+  let webgl: WebglAddon | null = null;
+  let dprMedia: MediaQueryList | null = null;
+
+  // The glyph atlas is rasterised for one device pixel ratio. Dragging the
+  // window to a display with a different one (or an Android browser-zoom
+  // change) leaves every cell blurry until the atlas is rebuilt.
+  const onDprChange = () => {
+    try {
+      term.clearTextureAtlas();
+    } catch {
+      // ignore — nothing to rebuild if the renderer already went away
+    }
+    watchDpr();
+  };
+
+  function watchDpr(): void {
+    dprMedia?.removeEventListener("change", onDprChange);
+    dprMedia = null;
+    try {
+      dprMedia = window.matchMedia?.(`(resolution: ${window.devicePixelRatio}dppx)`) ?? null;
+      dprMedia?.addEventListener("change", onDprChange);
+    } catch {
+      // ignore — a browser without `resolution` media queries just keeps the
+      // atlas it has, which is the pre-WebGL behaviour anyway
+    }
+  }
+
+  function releaseWebgl(): void {
+    dprMedia?.removeEventListener("change", onDprChange);
+    dprMedia = null;
+    if (!webgl) return;
+    const addon = webgl;
+    webgl = null;
+    try {
+      addon.dispose(); // xterm falls back to the DOM renderer
+    } catch {
+      // ignore — a lost context can throw on the way out
+    }
+  }
+
+  function acquireWebgl(): void {
+    if (webgl || disposed || !webglPolicy.enabled()) return;
+    try {
+      const addon = new WebglAddon();
+      // Context loss is routine on Android — backgrounding the tab is enough.
+      // Drop back to the DOM renderer, then retry only while the shared budget
+      // allows and this view is still the one on screen.
+      addon.onContextLoss(() => {
+        webglPolicy.noteContextLoss();
+        releaseWebgl();
+        if (mounted) acquireWebgl();
+      });
+      term.loadAddon(addon);
+      webgl = addon;
+      watchDpr();
+    } catch {
+      // Context creation failed outright (no GPU, or the browser is already at
+      // its context cap). Count it like a loss so we stop asking, and stay on
+      // the DOM renderer.
+      webglPolicy.noteContextLoss();
+      webgl = null;
+    }
+  }
+
   // Plain Escape hands the keyboard back to the session list instead of the
-  // shell/app. `false` tells xterm to skip its own handling of this event.
+  // shell/app. `false` tells xterm to skip its own handling of this event —
+  // which is also why the set doesn't `preventDefault`: swallowing here is
+  // xterm's return value, not the browser's.
   term.attachCustomKeyEventHandler((e) => {
-    if (e.type !== "keydown" || e.key !== "Escape") return true;
-    if (e.ctrlKey || e.altKey || e.metaKey || e.shiftKey) return true;
-    document.dispatchEvent(new CustomEvent(FOCUS_SIDEBAR_EVENT));
-    return false;
+    if (e.type !== "keydown") return true;
+    return !paneKeys.handle(e);
   });
 
   // Touch scrolling: xterm's built-in touch handling is jittery (drags crawl a
@@ -237,6 +319,10 @@ export function createAttachConnection(
   }
 
   let mounted = false;
+  // A previewed pane is visible but must not steal the keyboard from the
+  // sidebar, so mounting can opt out of the focus grab (and out of the one
+  // the socket does when it finishes connecting).
+  let focusOnMount = true;
   // We compute the fit ourselves instead of FitAddon.fit(): the addon subtracts
   // a scrollbar width that xterm reports as `offsetWidth - scrollArea || 15`,
   // so with the scrollbar hidden it falls back to a phantom 15px and the grid
@@ -315,7 +401,7 @@ export function createAttachConnection(
       reconnectMs = INITIAL_RECONNECT_MS;
       setState("connected", "open");
       sendControl({ type: "Resize", cols: term.cols, rows: term.rows });
-      if (mounted) term.focus();
+      if (mounted && focusOnMount) term.focus();
     };
 
     ws.onmessage = (ev) => {
@@ -400,17 +486,22 @@ export function createAttachConnection(
   return {
     sessionId,
     el,
-    onMount() {
+    onMount(mountOpts?: { focus?: boolean }) {
       mounted = true;
+      focusOnMount = mountOpts?.focus !== false;
+      acquireWebgl();
       // Defer a tick so the element has its content-pane dimensions before fit.
       requestAnimationFrame(() => {
         tryFit();
         sendControl({ type: "Resize", cols: term.cols, rows: term.rows });
-        if (ws.readyState === WebSocket.OPEN) term.focus();
+        if (focusOnMount && ws.readyState === WebSocket.OPEN) term.focus();
       });
     },
     onUnmount() {
       mounted = false;
+      // Parked views hand their GPU context back: the browser's cap is small
+      // (smaller still on Android) and MAX_PARKED connections outlive the pane.
+      releaseWebgl();
     },
     focusTerminal() {
       term.focus();
@@ -427,6 +518,7 @@ export function createAttachConnection(
       visual?.removeEventListener("resize", onResize);
       dataDisp.dispose();
       resizeDisp.dispose();
+      releaseWebgl();
       try {
         ws.close();
       } catch {

web/src/catalog.ts

@@ -2,7 +2,8 @@ import { escapeHtml } from "./html.js";
 import { ApiRequestError, getDaemonInfo, killSession, renameSession } from "./api.js";
 import { openForceKillDialog } from "./killDialog.js";
 import { openContextMenu } from "./contextMenu.js";
-import { isTypingTarget, toggleHelp } from "./help.js";
+import { toggleHelp } from "./help.js";
+import { CommandSet, defineCommands } from "./commands.js";
 import { CatalogStore } from "./events.js";
 import type { InTheWay, Session } from "./types.js";
 import {
@@ -164,6 +165,10 @@ function renderNode(node: TreeNode, depth: number): HTMLElement {
     return wrap;
   }
 
+  // The row outlives the snapshot it was built from: a refresh that changes
+  // nothing structural patches it in place rather than replacing it, so the
+  // handlers below have to read the current session, not the one captured here.
+  let cur = node.session;
   const s = node.session;
   const now = Date.now();
   const row = document.createElement("a");
@@ -197,33 +202,74 @@ function renderNode(node: TreeNode, depth: number): HTMLElement {
   similarBtn.addEventListener("click", (ev) => {
     ev.preventDefault();
     ev.stopPropagation();
-    document.dispatchEvent(new CustomEvent(SPAWN_SIMILAR_EVENT, { detail: s }));
+    document.dispatchEvent(new CustomEvent(SPAWN_SIMILAR_EVENT, { detail: cur }));
   });
   const killBtn = row.querySelector(".leaf-kill") as HTMLButtonElement;
   killBtn.addEventListener("click", (ev) => {
     ev.preventDefault();
     ev.stopPropagation();
-    void requestKill(s, name);
+    void requestKill(cur, sessionName(cur));
   });
   row.addEventListener("click", () => {
-    document.dispatchEvent(new CustomEvent(SESSION_SELECT_EVENT, { detail: s.id }));
+    document.dispatchEvent(new CustomEvent(SESSION_SELECT_EVENT, { detail: cur.id }));
   });
   row.addEventListener("contextmenu", (ev) => {
     ev.preventDefault();
     ev.stopPropagation();
     openContextMenu(ev.clientX, ev.clientY, [
-      { label: "Rename…", onSelect: () => beginRename(row, s) },
+      { label: "Rename…", onSelect: () => beginRename(row, cur) },
       {
         label: "Spawn similar",
         onSelect: () =>
-          document.dispatchEvent(new CustomEvent(SPAWN_SIMILAR_EVENT, { detail: s })),
+          document.dispatchEvent(new CustomEvent(SPAWN_SIMILAR_EVENT, { detail: cur })),
+      },
+      {
+        label: "Kill session",
+        danger: true,
+        onSelect: () => void requestKill(cur, sessionName(cur)),
       },
-      { label: "Kill session", danger: true, onSelect: () => void requestKill(s, name) },
     ]);
   });
+  leafPatches.set(row, (next) => {
+    cur = next;
+    const nextSlug = activityColorSlug(next.activity ?? "Idle");
+    const nextWord = STATE_WORDS[nextSlug] ?? STATE_WORDS.idle;
+    row.setAttribute(
+      "aria-label",
+      `${sessionName(next)}, ${next.status === "Running" ? "running" : "exited"}, ${nextWord}`,
+    );
+    const rail = row.querySelector(".activity-rail");
+    if (rail) rail.outerHTML = activityRailMarkup(nextSlug, nextWord);
+    const meta = row.querySelector(".card-line2");
+    if (meta) meta.outerHTML = metaLine(next, Date.now());
+  });
   return row;
 }
 
+/** Refresh a standing card from a newer snapshot of its session, keeping the
+ *  element (and so the pointer's `:hover`) exactly where it is. Registered by
+ *  `renderNode`; only the bits `treeSignature` leaves out are rewritten. */
+const leafPatches = new WeakMap<HTMLElement, (s: Session) => void>();
+
+/**
+ * Everything about the tree that a patch cannot fix up.
+ *
+ * The daemon re-sends a session on every activity, foreground or cwd shift —
+ * a couple of times a minute per live session — and rebuilding the sidebar for
+ * each one drops `:hover` from the row under the pointer. Refreshes whose
+ * signature is unchanged are patched into the standing rows instead; anything
+ * that moves, renames, appears or dies changes the signature and rebuilds.
+ */
+function treeSignature(node: TreeNode): string {
+  if (node.kind === "folder") {
+    const head = `F:${node.name}:${node.path}:${collapsed.has(node.path)}`;
+    if (node.name && collapsed.has(node.path)) return head;
+    return `${head}(${node.children.map(treeSignature).join(",")})`;
+  }
+  const s = node.session;
+  return `L:${s.id}:${sessionName(s)}:${s.status}:${isProvisionalName(s)}`;
+}
+
 /**
  * Kill on the first click (#81): the daemon is the one that decides whether a
  * session may go, and it refuses over a worktree holding unsaved work. Only
@@ -364,6 +410,11 @@ export interface SidebarOptions {
   /** Daemon link behind the footer's status dot. Omitted in tests and in the
    *  design kit, which render the sidebar without a daemon. */
   link?: DaemonLink;
+  /** The highlight moved onto a session, or off every session (`null`): the
+   *  shell shows it in the content pane without opening it (docs/PREVIEW.md).
+   *  `source` is there so a mouse sweep can be debounced differently from a
+   *  keyboard step. */
+  onPreview?: (sessionId: string | null) => void;
 }
 
 export function renderSidebar(store: CatalogStore, opts: SidebarOptions = {}): SidebarHandle {
@@ -528,6 +579,9 @@ export function renderSidebar(store: CatalogStore, opts: SidebarOptions = {}): S
     for (const r of rows) r.classList.toggle("is-highlighted", r.dataset.navKey === navKey);
   };
 
+  const sessionOf = (key: string | null): string | null =>
+    key?.startsWith("session:") ? key.slice("session:".length) : null;
+
   const moveNav = (delta: number) => {
     const rows = navRows();
     if (rows.length === 0) return;
@@ -539,6 +593,7 @@ export function renderSidebar(store: CatalogStore, opts: SidebarOptions = {}): S
     navKey = next.dataset.navKey ?? null;
     applyNav();
     next.scrollIntoView({ block: "nearest" });
+    opts.onPreview?.(sessionOf(navKey));
   };
 
   /** Enter: open the highlighted session, or expand the highlighted folder. */
@@ -563,20 +618,77 @@ export function renderSidebar(store: CatalogStore, opts: SidebarOptions = {}): S
     applyNav();
   };
 
+  // Hover previews the row under the pointer (docs/PREVIEW.md). Touch is left
+  // out: there is no hover there, and a tap already opens the session.
+  let hovered: string | null = null;
+  const setHovered = (id: string | null) => {
+    if (hovered === id) return;
+    hovered = id;
+    opts.onPreview?.(id);
+  };
+  treeHost.addEventListener("pointerover", (e) => {
+    if (e.pointerType === "touch") return;
+    const row = (e.target as HTMLElement | null)?.closest<HTMLElement>(".tree-leaf");
+    setHovered(row?.dataset.sessionId ?? null);
+  });
+  treeHost.addEventListener("pointerleave", (e) => {
+    if (e.pointerType === "touch") return;
+    setHovered(null);
+  });
+
   // Focusable as a unit: the walk moves a highlight, not DOM focus, so the
   // keyboard stays here while j/k runs.
   treeHost.tabIndex = -1;
-  treeHost.addEventListener("keydown", (e) => {
-    if (e.ctrlKey || e.altKey || e.metaKey) return;
-    // The inline rename field lives inside a row and owns its own keys.
-    if (isTypingTarget(e.target)) return;
-    if (e.key === "j" || e.key === "ArrowDown") moveNav(1);
-    else if (e.key === "k" || e.key === "ArrowUp") moveNav(-1);
-    else if (e.key === "Enter") activateNav();
-    else if (e.key === "Tab") document.dispatchEvent(new CustomEvent(FOCUS_PANE_EVENT));
-    else return;
-    e.preventDefault();
-  });
+  // The keyboard walk's preview belongs to the list having the keyboard: once
+  // it doesn't, the content pane goes back to what the operator actually opened.
+  treeHost.addEventListener("blur", () => opts.onPreview?.(null));
+
+  /** The session behind the highlighted row, if the highlight is on a card. */
+  const highlightedSession = (): { row: HTMLElement; session: Session } | undefined => {
+    const row = rowFor(navKey);
+    const id = row?.dataset.sessionId;
+    if (!row || !id) return undefined;
+    const session = store.snapshot().sessions.get(id);
+    return session ? { row, session } : undefined;
+  };
+
+  /** `c`: collapse or expand the highlighted folder, the TUI's
+   *  `ToggleSidebarGroup`. Clicking the header is what toggles it; on a card
+   *  the key does nothing rather than toggling some other folder. */
+  const toggleHighlightedFolder = () => {
+    const row = rowFor(navKey);
+    if (!row || !row.classList.contains("tree-folder-header")) return;
+    row.click();
+    applyNav();
+  };
+
+  // The session list's half of the command registry (#148). One set per
+  // sidebar, so a second sidebar (tests, hot reload) drives its own rows; the
+  // labels and chords still come from the one registry.
+  const listKeys = new CommandSet(
+    defineCommands({
+      "list.next": () => moveNav(1),
+      "list.prev": () => moveNav(-1),
+      "list.activate": () => activateNav(),
+      "list.toggleFolder": () => toggleHighlightedFolder(),
+      "list.rename": () => {
+        const hit = highlightedSession();
+        if (hit) beginRename(hit.row, hit.session);
+      },
+      "list.kill": () => {
+        const hit = highlightedSession();
+        if (hit) void requestKill(hit.session, sessionName(hit.session));
+      },
+      "list.focusPane": () => document.dispatchEvent(new CustomEvent(FOCUS_PANE_EVENT)),
+    }),
+  );
+
+  // The inline rename field lives inside a row and owns its own keys; the set's
+  // plain-key rule keeps this walk out of it.
+  treeHost.addEventListener("keydown", (e) => listKeys.handle(e));
+
+  /** Signature of what is currently on screen — see `treeSignature`. */
+  let renderedSignature: string | null = null;
 
   const refresh = () => {
     // Rebuilding the tree now would blow away the field being typed into.
@@ -584,6 +696,15 @@ export function renderSidebar(store: CatalogStore, opts: SidebarOptions = {}): S
     const state = store.snapshot();
     const sessions = [...state.sessions.values()];
     const tree = buildTree(sessions, homeDir, filter);
+    const signature = sessions.length === 0 ? `EMPTY:${filter.trim()}` : treeSignature(tree);
+    if (signature === renderedSignature) {
+      for (const row of treeHost.querySelectorAll<HTMLElement>(".tree-leaf")) {
+        const s = row.dataset.sessionId ? state.sessions.get(row.dataset.sessionId) : undefined;
+        if (s) leafPatches.get(row)?.(s);
+      }
+      return;
+    }
+    renderedSignature = signature;
     treeHost.replaceChildren();
     if (sessions.length === 0) {
       treeHost.appendChild(
@@ -607,7 +728,13 @@ export function renderSidebar(store: CatalogStore, opts: SidebarOptions = {}): S
       /* absolute paths are a fine fallback */
     });
 
-  const rerenderHandler = () => refresh();
+  // Dispatched when something outside the store changed what the tree should
+  // look like — a folder collapsed, a rename ended — none of which the store
+  // snapshot can show, so the signature check has to be bypassed.
+  const rerenderHandler = () => {
+    renderedSignature = null;
+    refresh();
+  };
   document.addEventListener("catalog-rerender", rerenderHandler);
 
   // "Spawn similar" (#28) is dispatched here and handled in main.ts, where the

web/src/catalogPatch.test.ts

@@ -0,0 +1,105 @@
+// @vitest-environment happy-dom
+import { beforeAll, describe, expect, it } from "vitest";
+
+import { renderSidebar } from "./catalog.js";
+import type { CatalogListener, CatalogStore } from "./events.js";
+import type { Session } from "./types.js";
+
+beforeAll(() => {
+  Object.defineProperty(window, "localStorage", {
+    value: { getItem: () => null, setItem: () => {} },
+  });
+  window.fetch = () => Promise.reject(new Error("offline"));
+});
+
+const ID = "11111111-2222-3333-4444-555555555555";
+
+function session(overrides: Partial<Session> = {}): Session {
+  return {
+    id: ID,
+    cwd: "/home/naps/tea/maestro",
+    command: "claude",
+    env: {},
+    metadata: {},
+    status: "Running",
+    created_at: "2026-08-24T10:00:00Z",
+    ...overrides,
+  };
+}
+
+/** A store whose updates actually reach subscribers, unlike the one-shot
+ *  harness in catalog.test.ts. */
+function liveStore(initial: Session[]) {
+  const state = { sessions: new Map(initial.map((s) => [s.id, s])) };
+  const listeners = new Set<CatalogListener>();
+  const store = {
+    snapshot: () => state,
+    subscribe: (fn: CatalogListener) => {
+      listeners.add(fn);
+      fn(state);
+      return () => listeners.delete(fn);
+    },
+  } as unknown as CatalogStore;
+  const push = (sessions: Session[]) => {
+    state.sessions = new Map(sessions.map((s) => [s.id, s]));
+    for (const fn of listeners) fn(state);
+  };
+  return { store, push };
+}
+
+const rowOf = (el: HTMLElement) => el.querySelector<HTMLElement>(".tree-leaf")!;
+
+describe("sidebar refresh keeps rows in place (docs/SIDEBAR.md)", () => {
+  it("patches an activity change into the standing row instead of rebuilding it", () => {
+    const { store, push } = liveStore([session({ activity: "Idle" })]);
+    const { el } = renderSidebar(store, {});
+    const before = rowOf(el);
+
+    push([session({ activity: "AwaitingInput" })]);
+
+    // Same element: a rebuild under the pointer would drop `:hover` and restart
+    // the row's transitions, which is the flicker this avoids.
+    expect(rowOf(el)).toBe(before);
+    // …and the card still tells the truth about the session.
+    expect(before.querySelector(".activity-rail")?.getAttribute("data-activity")).toBe(
+      "awaiting-input",
+    );
+    expect(before.querySelector(".card-line2")?.getAttribute("data-activity")).toBe(
+      "awaiting-input",
+    );
+    expect(before.getAttribute("aria-label")).toContain("Awaiting input");
+  });
+
+  it("rebuilds when the row set changes", () => {
+    const { store, push } = liveStore([session()]);
+    const { el } = renderSidebar(store, {});
+    const before = rowOf(el);
+
+    push([session(), session({ id: "99999999-2222-3333-4444-555555555555", command: "bash" })]);
+
+    expect(el.querySelectorAll(".tree-leaf")).toHaveLength(2);
+    expect(rowOf(el)).not.toBe(before);
+  });
+
+  it("rebuilds when a session dies", () => {
+    const { store, push } = liveStore([session()]);
+    const { el } = renderSidebar(store, {});
+    const before = rowOf(el);
+
+    push([session({ status: "Dead" })]);
+
+    expect(rowOf(el)).not.toBe(before);
+    expect(rowOf(el).dataset.status).toBe("dead");
+  });
+
+  it("rebuilds when a session is renamed", () => {
+    const { store, push } = liveStore([session()]);
+    const { el } = renderSidebar(store, {});
+    const before = rowOf(el);
+
+    push([session({ metadata: { name: "harmony" } })]);
+
+    expect(rowOf(el)).not.toBe(before);
+    expect(rowOf(el).querySelector(".leaf-name")?.textContent).toBe("harmony");
+  });
+});

web/src/commands.test.ts

@@ -0,0 +1,236 @@
+// @vitest-environment happy-dom
+import { describe, expect, it, vi } from "vitest";
+
+import {
+  COMMAND_SPECS,
+  CommandSet,
+  DEFAULT_LEADER,
+  canonicalizeKey,
+  defineCommands,
+  isTypingTarget,
+  keyCaps,
+  publishedCommands,
+} from "./commands.js";
+
+function key(k: string, init: KeyboardEventInit = {}): KeyboardEvent {
+  return new KeyboardEvent("keydown", { key: k, cancelable: true, ...init });
+}
+
+function el(html: string): HTMLElement {
+  const d = document.createElement("div");
+  d.innerHTML = html;
+  return d.firstElementChild as HTMLElement;
+}
+
+/** Dispatch on a target, so `isTypingTarget` sees something other than null. */
+function pressOn(set: CommandSet, target: HTMLElement, k: string, init?: KeyboardEventInit): boolean {
+  const e = key(k, init);
+  Object.defineProperty(e, "target", { value: target });
+  return set.handle(e);
+}
+
+describe("command specs", () => {
+  it("has a unique id and at least one chord per command", () => {
+    const ids = COMMAND_SPECS.map((s) => s.id);
+    expect(new Set(ids).size).toBe(ids.length);
+    for (const spec of COMMAND_SPECS) {
+      expect(spec.keys.length).toBeGreaterThan(0);
+      expect(spec.label.length).toBeGreaterThan(0);
+    }
+  });
+
+  it("binds each chord once within a scope", () => {
+    const seen = new Set<string>();
+    for (const spec of COMMAND_SPECS) {
+      for (const k of spec.keys) {
+        const slot = `${spec.scope}:${k}`;
+        expect(seen.has(slot)).toBe(false);
+        seen.add(slot);
+      }
+    }
+  });
+
+  it("rejects a handler for an id that isn't in the registry", () => {
+    expect(() => defineCommands({ "nope.missing": () => {} })).toThrow(/unknown command id/);
+  });
+
+  it("carries every spec field onto the defined command", () => {
+    const [cmd] = defineCommands({ "spawn.open": () => {} });
+    expect(cmd).toMatchObject({ id: "spawn.open", keys: ["n"], scope: "global" });
+  });
+});
+
+describe("canonicalizeKey", () => {
+  it("spells keys the way the TUI's InputKey::canonical does", () => {
+    expect(canonicalizeKey(key("n"))).toBe("n");
+    expect(canonicalizeKey(key("N", { shiftKey: true }))).toBe("N");
+    expect(canonicalizeKey(key("?", { shiftKey: true }))).toBe("?");
+    expect(canonicalizeKey(key("a", { ctrlKey: true }))).toBe("ctrl-a");
+    expect(canonicalizeKey(key("Escape"))).toBe("esc");
+    expect(canonicalizeKey(key("Enter"))).toBe("enter");
+    expect(canonicalizeKey(key("Tab"))).toBe("tab");
+    expect(canonicalizeKey(key("Tab", { shiftKey: true }))).toBe("backtab");
+    expect(canonicalizeKey(key("ArrowDown"))).toBe("down");
+  });
+
+  it("folds a modified letter to lower case with an explicit shift-", () => {
+    expect(canonicalizeKey(key("H", { ctrlKey: true, shiftKey: true }))).toBe("ctrl-shift-h");
+    expect(canonicalizeKey(key("h", { ctrlKey: true, shiftKey: true }))).toBe("ctrl-shift-h");
+  });
+
+  it("has no canonical form for a modifier pressed alone", () => {
+    expect(canonicalizeKey(key("Control", { ctrlKey: true }))).toBeNull();
+    expect(canonicalizeKey(key("Shift", { shiftKey: true }))).toBeNull();
+  });
+});
+
+describe("keyCaps", () => {
+  it("renders one cap per modifier and key", () => {
+    expect(keyCaps("ctrl-shift-h")).toEqual(["Ctrl", "Shift", "H"]);
+    expect(keyCaps("enter")).toEqual(["Enter"]);
+    expect(keyCaps("j")).toEqual(["j"]);
+    expect(keyCaps("N")).toEqual(["N"]);
+    expect(keyCaps("?")).toEqual(["?"]);
+    expect(keyCaps("ctrl-a ctrl-k")).toEqual(["Ctrl", "A", "then", "Ctrl", "K"]);
+  });
+});
+
+describe("CommandSet", () => {
+  it("runs the command bound to a chord, and swallows the browser default", () => {
+    const run = vi.fn();
+    const set = new CommandSet(defineCommands({ "spawn.open": run }));
+    const e = key("n");
+    expect(set.handle(e)).toBe(true);
+    expect(run).toHaveBeenCalledTimes(1);
+    expect(e.defaultPrevented).toBe(true);
+  });
+
+  it("leaves an unbound key alone", () => {
+    const set = new CommandSet(defineCommands({ "spawn.open": vi.fn() }));
+    const e = key("q");
+    expect(set.handle(e)).toBe(false);
+    expect(e.defaultPrevented).toBe(false);
+  });
+
+  it("treats a modified key as a different binding", () => {
+    const run = vi.fn();
+    const set = new CommandSet(defineCommands({ "spawn.open": run }));
+    expect(set.handle(key("n", { ctrlKey: true }))).toBe(false);
+    expect(set.handle(key("n", { metaKey: true }))).toBe(false);
+    expect(run).not.toHaveBeenCalled();
+  });
+
+  it("runs every alias of a command", () => {
+    const run = vi.fn();
+    const set = new CommandSet(defineCommands({ "list.next": run }));
+    set.handle(key("j"));
+    set.handle(key("ArrowDown"));
+    expect(run).toHaveBeenCalledTimes(2);
+  });
+
+  it("keeps plain keys deaf inside a form field, and chorded ones live", () => {
+    const plain = vi.fn();
+    const chorded = vi.fn();
+    const set = new CommandSet(
+      defineCommands({ "spawn.open": plain, "focus.toggle": chorded }),
+    );
+    const input = el("<input>");
+    expect(pressOn(set, input, "n")).toBe(false);
+    expect(plain).not.toHaveBeenCalled();
+    expect(pressOn(set, input, "H", { ctrlKey: true, shiftKey: true })).toBe(true);
+    expect(chorded).toHaveBeenCalledTimes(1);
+  });
+
+  it("keeps pane commands live inside the terminal's textarea", () => {
+    const run = vi.fn();
+    const set = new CommandSet(defineCommands({ "pane.focusList": run }), {
+      preventDefault: false,
+    });
+    const textarea = el('<textarea class="xterm-helper-textarea"></textarea>');
+    const e = key("Escape");
+    Object.defineProperty(e, "target", { value: textarea });
+    expect(set.handle(e)).toBe(true);
+    expect(run).toHaveBeenCalledTimes(1);
+    // xterm is told to swallow by the return value, not by the browser default.
+    expect(e.defaultPrevented).toBe(false);
+  });
+});
+
+describe("the leader", () => {
+  it("defaults to the TUI's ctrl-a", () => {
+    expect(DEFAULT_LEADER).toBe("ctrl-a");
+  });
+
+  it("holds the leader as a partial chord instead of selecting the page", () => {
+    const set = new CommandSet(defineCommands({ "spawn.open": vi.fn() }), {
+      leader: DEFAULT_LEADER,
+    });
+    const e = key("a", { ctrlKey: true });
+    expect(set.handle(e)).toBe(true);
+    expect(e.defaultPrevented).toBe(true);
+  });
+
+  it("swallows the key after the leader rather than running its plain binding", () => {
+    const run = vi.fn();
+    const set = new CommandSet(defineCommands({ "spawn.open": run }), {
+      leader: DEFAULT_LEADER,
+    });
+    set.handle(key("a", { ctrlKey: true }));
+    expect(set.handle(key("n"))).toBe(true);
+    expect(run).not.toHaveBeenCalled();
+    // The next key is an ordinary one again.
+    set.handle(key("n"));
+    expect(run).toHaveBeenCalledTimes(1);
+  });
+
+  it("forgets a held leader once the chord timeout passes", () => {
+    const run = vi.fn();
+    let now = 0;
+    const set = new CommandSet(defineCommands({ "spawn.open": run }), {
+      leader: DEFAULT_LEADER,
+      chordTimeoutMs: 1000,
+      now: () => now,
+    });
+    set.handle(key("a", { ctrlKey: true }));
+    now = 1500;
+    set.handle(key("n"));
+    expect(run).toHaveBeenCalledTimes(1);
+  });
+
+  it("leaves select-all alone in a real form field", () => {
+    const set = new CommandSet(defineCommands({ "spawn.open": vi.fn() }), {
+      leader: DEFAULT_LEADER,
+    });
+    const input = el("<input>");
+    const e = key("a", { ctrlKey: true });
+    Object.defineProperty(e, "target", { value: input });
+    expect(set.handle(e)).toBe(false);
+    expect(e.defaultPrevented).toBe(false);
+  });
+});
+
+describe("publishing", () => {
+  it("lists a constructed set's commands, replacing an id rather than doubling it", () => {
+    new CommandSet(defineCommands({ "list.kill": () => {} }));
+    new CommandSet(defineCommands({ "list.kill": () => {} }));
+    const ids = publishedCommands().map((c) => c.id);
+    expect(ids.filter((id) => id === "list.kill")).toEqual(["list.kill"]);
+  });
+
+  it("keeps published commands in registry order", () => {
+    const order = COMMAND_SPECS.map((s) => s.id);
+    const ids = publishedCommands().map((c) => c.id);
+    expect(ids).toEqual(order.filter((id) => ids.includes(id)));
+  });
+});
+
+describe("isTypingTarget", () => {
+  it("is true for form fields and editable nodes, false otherwise", () => {
+    expect(isTypingTarget(el("<input>"))).toBe(true);
+    expect(isTypingTarget(el("<textarea></textarea>"))).toBe(true);
+    expect(isTypingTarget(el("<select></select>"))).toBe(true);
+    expect(isTypingTarget(el('<div contenteditable="true"></div>'))).toBe(true);
+    expect(isTypingTarget(el("<button></button>"))).toBe(false);
+    expect(isTypingTarget(null)).toBe(false);
+  });
+});

web/src/commands.ts

@@ -0,0 +1,386 @@
+// The web client's command registry (#148). One entry per command — a stable
+// id, a plain-language label, the key chord it answers to, and a `run()` — so
+// there is exactly one list of what the client can do. The `?` overlay renders
+// from it (`help.ts`), and every keybinding is dispatched through it; a command
+// added here is bound and documented in the same edit.
+//
+// Keys are canonical strings, the same spelling the TUI's `InputKey::canonical`
+// produces (`ctrl-shift-h`, `enter`, `esc`, `n`, `N`) and chords are those
+// joined by a space (`ctrl-a ctrl-k`). Matching the TUI's spelling is what lets
+// docs/COMMAND-BAR.md describe one key model for both clients.
+
+/** Where a command's keys are listened for. `global` is the window, `list` the
+ *  sidebar's session tree, `pane` the attached terminal, `overlay` the help
+ *  dialog while it is up. */
+export type CommandScope = "global" | "list" | "pane" | "overlay";
+
+export interface CommandSpec {
+  /** Stable identifier. Never rendered; safe to bind config and tests to. */
+  id: string;
+  /** Plain-language label — what the `?` overlay and (later) the command bar
+   *  show. */
+  label: string;
+  /** Help-overlay section. Groups render in the order they first appear here. */
+  group: string;
+  /** Canonical chords that run it. The first is the one shown to the operator;
+   *  the rest are aliases (`j` and `down`). */
+  keys: string[];
+  scope: CommandScope;
+}
+
+export interface Command extends CommandSpec {
+  run: () => void;
+}
+
+/** Every command the web client has. The single list this issue exists to
+ *  create: labels, chords and grouping live here and nowhere else. */
+export const COMMAND_SPECS: readonly CommandSpec[] = [
+  {
+    id: "spawn.open",
+    label: "Open the spawn form",
+    group: "Sessions",
+    keys: ["n"],
+    scope: "global",
+  },
+  {
+    id: "spawn.fastForward",
+    label: "Spawn a session with every default resolved",
+    group: "Sessions",
+    keys: ["N"],
+    scope: "global",
+  },
+  {
+    id: "focus.toggle",
+    label: "Move the keyboard between the session list and the pane",
+    group: "Session list",
+    keys: ["ctrl-shift-h"],
+    scope: "global",
+  },
+  {
+    id: "list.next",
+    label: "Highlight the next session",
+    group: "Session list",
+    keys: ["j", "down"],
+    scope: "list",
+  },
+  {
+    id: "list.prev",
+    label: "Highlight the previous session",
+    group: "Session list",
+    keys: ["k", "up"],
+    scope: "list",
+  },
+  {
+    id: "list.activate",
+    label: "Open the highlighted session, or expand a folder",
+    group: "Session list",
+    keys: ["enter"],
+    scope: "list",
+  },
+  {
+    id: "list.toggleFolder",
+    label: "Collapse or expand the highlighted folder",
+    group: "Session list",
+    keys: ["c"],
+    scope: "list",
+  },
+  {
+    id: "list.rename",
+    label: "Rename the highlighted session",
+    group: "Session list",
+    keys: ["r"],
+    scope: "list",
+  },
+  {
+    id: "list.kill",
+    label: "Kill the highlighted session",
+    group: "Session list",
+    keys: ["x"],
+    scope: "list",
+  },
+  {
+    id: "list.focusPane",
+    label: "Send the keyboard to the pane",
+    group: "Session list",
+    keys: ["tab"],
+    scope: "list",
+  },
+  {
+    id: "pane.focusList",
+    label: "Hand the keyboard back to the session list, from the pane",
+    group: "Session list",
+    keys: ["esc"],
+    scope: "pane",
+  },
+  {
+    id: "help.toggle",
+    label: "Show or hide this help",
+    group: "Help",
+    keys: ["?"],
+    scope: "global",
+  },
+  {
+    id: "help.close",
+    label: "Close the help overlay or an open menu",
+    group: "Help",
+    keys: ["esc"],
+    scope: "overlay",
+  },
+  {
+    id: "debug.toggleHud",
+    label: "Toggle the debug HUD",
+    group: "Debug",
+    keys: ["ctrl-shift-d"],
+    scope: "global",
+  },
+];
+
+const SPEC_BY_ID = new Map(COMMAND_SPECS.map((s) => [s.id, s]));
+
+/** Attach handlers to specs, by id. Throws on an unknown id, so a typo is a
+ *  test failure rather than a key that silently does nothing. */
+export function defineCommands(handlers: Record<string, () => void>): Command[] {
+  return Object.entries(handlers).map(([id, run]) => {
+    const spec = SPEC_BY_ID.get(id);
+    if (!spec) throw new Error(`unknown command id: ${id}`);
+    return { ...spec, run };
+  });
+}
+
+// ---- what the help overlay renders ----
+
+const published = new Map<string, Command>();
+
+/** Record commands as bound. Re-registering an id replaces it, so a second
+ *  sidebar (tests, hot reload) doesn't duplicate rows in the overlay. */
+export function publishCommands(cmds: Command[]): void {
+  for (const c of cmds) published.set(c.id, c);
+}
+
+/** Every bound command, in `COMMAND_SPECS` order. */
+export function publishedCommands(): Command[] {
+  return COMMAND_SPECS.map((s) => published.get(s.id)).filter((c): c is Command => c !== undefined);
+}
+
+// ---- key canonicalisation ----
+
+const NAMED: Record<string, string> = {
+  Escape: "esc",
+  Enter: "enter",
+  Tab: "tab",
+  Backspace: "backspace",
+  ArrowUp: "up",
+  ArrowDown: "down",
+  ArrowLeft: "left",
+  ArrowRight: "right",
+  Home: "home",
+  End: "end",
+  PageUp: "pageup",
+  PageDown: "pagedown",
+  Delete: "delete",
+  " ": "space",
+};
+
+/** The canonical string for one keydown. Mirrors the TUI's
+ *  `InputKey::canonical`: modifier prefixes in ctrl/alt/shift order, then the
+ *  key. A shifted character already spells itself (`N`, `?`), so `shift-` is
+ *  only written when another modifier is present and the char was folded to
+ *  lower case. */
+export function canonicalizeKey(e: KeyboardEvent): string | null {
+  if (!e.key) return null;
+  // Modifier keys pressed alone are never a binding.
+  if (e.key === "Control" || e.key === "Alt" || e.key === "Shift" || e.key === "Meta") return null;
+  const named = NAMED[e.key];
+  if (named === "tab" && e.shiftKey) return "backtab";
+  let out = "";
+  if (e.ctrlKey) out += "ctrl-";
+  if (e.altKey) out += "alt-";
+  if (e.metaKey) out += "meta-";
+  if (named) {
+    if (e.shiftKey) out += "shift-";
+    return out + named;
+  }
+  if (e.key.length === 1) {
+    if (out === "") return e.key;
+    if (e.shiftKey) out += "shift-";
+    return out + e.key.toLowerCase();
+  }
+  if (e.shiftKey) out += "shift-";
+  return out + e.key.toLowerCase();
+}
+
+const MOD_PREFIX = /^(ctrl|alt|meta|shift)-/;
+
+/** True when a chord carries a modifier or more than one key. Plain single-key
+ *  chords are the ones that stay deaf inside form fields. */
+function isChorded(chord: string): boolean {
+  return chord.includes(" ") || MOD_PREFIX.test(chord);
+}
+
+/** True when the event target swallows plain keystrokes — a form field, or the
+ *  hidden textarea xterm types into. Every plain single-key binding is deaf in
+ *  the same places. */
+export function isTypingTarget(target: EventTarget | null): boolean {
+  const el = target as HTMLElement | null;
+  if (!el || typeof el.tagName !== "string") return false;
+  return (
+    el.tagName === "INPUT" ||
+    el.tagName === "TEXTAREA" ||
+    el.tagName === "SELECT" ||
+    el.isContentEditable
+  );
+}
+
+/** xterm's offscreen textarea. It is a typing target like any other, but it is
+ *  also where the leader has to work — a pane is exactly where the operator
+ *  needs the escape hatch (docs/COMMAND-BAR.md). */
+function isTerminalTextarea(target: EventTarget | null): boolean {
+  const el = target as HTMLElement | null;
+  return !!el && typeof el.className === "string" && el.classList?.contains("xterm-helper-textarea");
+}
+
+// ---- display ----
+
+const CAPS: Record<string, string> = {
+  ctrl: "Ctrl",
+  alt: "Alt",
+  meta: "Meta",
+  shift: "Shift",
+  esc: "Esc",
+  enter: "Enter",
+  tab: "Tab",
+  backtab: "Shift Tab",
+  backspace: "Backspace",
+  up: "Up",
+  down: "Down",
+  left: "Left",
+  right: "Right",
+  home: "Home",
+  end: "End",
+  pageup: "PgUp",
+  pagedown: "PgDn",
+  delete: "Del",
+  space: "Space",
+};
+
+/** Keycaps for a chord, left to right: `ctrl-shift-h` → Ctrl, Shift, H. A
+ *  multi-key chord separates its keys with a `then` cap. */
+export function keyCaps(chord: string): string[] {
+  const caps: string[] = [];
+  for (const [i, key] of chord.split(" ").entries()) {
+    if (i > 0) caps.push("then");
+    const parts = key.split("-");
+    // A bare `-` key splits into two empties; treat it as the key itself.
+    if (parts.every((p) => p === "")) {
+      caps.push("-");
+      continue;
+    }
+    const last = parts.pop() as string;
+    const mods = parts.filter((p) => p !== "");
+    for (const m of mods) caps.push(CAPS[m] ?? m);
+    caps.push(CAPS[last] ?? (mods.length > 0 && last.length === 1 ? last.toUpperCase() : last));
+  }
+  return caps;
+}
+
+// ---- dispatch ----
+
+/** Default leader, mirroring the TUI's `[tui].leader`. `ctrl-a` is select-all
+ *  in a browser, so a set that owns the leader `preventDefault`s it. */
+export const DEFAULT_LEADER = "ctrl-a";
+
+/** How long a partial chord waits for its next key — the TUI's
+ *  `chord_timeout_ms` default. */
+export const DEFAULT_CHORD_TIMEOUT_MS = 1000;
+
+export interface CommandSetOptions {
+  /** Canonical leader key. A set given one holds every leader press as a
+   *  pending chord, whether or not anything is bound behind it yet. */
+  leader?: string | null;
+  chordTimeoutMs?: number;
+  /** Call `preventDefault()` on a handled key. Off for the terminal's own key
+   *  handler, which swallows by returning `false` to xterm instead. */
+  preventDefault?: boolean;
+  /** Clock, for tests. */
+  now?: () => number;
+}
+
+/** A group of commands listening on one surface. Resolves a keydown to a
+ *  command the way the TUI's `ChordState` does: hold while the sequence is a
+ *  strict prefix of some binding, otherwise resolve and dispatch. */
+export class CommandSet {
+  private readonly byChord = new Map<string, Command>();
+  private readonly leader: string | null;
+  private readonly timeout: number;
+  private readonly preventDefault: boolean;
+  private readonly now: () => number;
+  private held: string[] = [];
+  private lastPress = 0;
+
+  constructor(
+    readonly commands: Command[],
+    opts: CommandSetOptions = {},
+  ) {
+    for (const c of commands) for (const k of c.keys) this.byChord.set(k, c);
+    this.leader = opts.leader ?? null;
+    this.timeout = opts.chordTimeoutMs ?? DEFAULT_CHORD_TIMEOUT_MS;
+    this.preventDefault = opts.preventDefault ?? true;
+    this.now = opts.now ?? (() => Date.now());
+    publishCommands(commands);
+  }
+
+  /** Whether any binding starts with `candidate` and continues. */
+  private isPrefix(candidate: string): boolean {
+    const marker = `${candidate} `;
+    for (const chord of this.byChord.keys()) if (chord.startsWith(marker)) return true;
+    return false;
+  }
+
+  /** Feed one keydown. Returns true when the key was consumed — dispatched, or
+   *  held as a partial chord. */
+  handle(e: KeyboardEvent): boolean {
+    const key = canonicalizeKey(e);
+    if (key === null) return false;
+    if (this.held.length > 0 && this.now() - this.lastPress > this.timeout) this.held = [];
+    const candidate = this.held.length > 0 ? `${this.held.join(" ")} ${key}` : key;
+    this.lastPress = this.now();
+
+    // The leader is a prefix by construction, so it stops being select-all
+    // before anything is bound behind it (#149 binds the first chord).
+    if (this.leader !== null && this.held.length === 0 && key === this.leader) {
+      if (isTypingTarget(e.target) && !isTerminalTextarea(e.target)) return false;
+      this.held = [key];
+      if (this.preventDefault) e.preventDefault();
+      return true;
+    }
+
+    if (this.isPrefix(candidate)) {
+      this.held.push(key);
+      if (this.preventDefault) e.preventDefault();
+      return true;
+    }
+
+    const wasChord = this.held.length > 0;
+    this.held = [];
+    const cmd = this.byChord.get(candidate);
+    if (!cmd) {
+      // A chord that resolved to nothing is still consumed: the leader took
+      // the key, so it must not also fall through to a plain binding.
+      return wasChord;
+    }
+    // Plain single-key bindings are deaf where typing happens; chorded ones are
+    // not, and neither are the pane's and the overlay's, which are only fed
+    // from the surface that owns them.
+    if (
+      !isChorded(candidate) &&
+      cmd.scope !== "pane" &&
+      cmd.scope !== "overlay" &&
+      isTypingTarget(e.target)
+    ) {
+      return false;
+    }
+    if (this.preventDefault) e.preventDefault();
+    cmd.run();
+    return true;
+  }
+}

web/src/connections.ts

@@ -74,7 +74,7 @@ export class ConnectionPool {
    * Ensure `id` is live and shown inside `pane`, reusing its connection if one
    * exists (refreshing LRU recency). Does not touch other mounted panes.
    */
-  mount(id: Uuid, pane: HTMLElement, info?: AttachInfo): void {
+  mount(id: Uuid, pane: HTMLElement, info?: AttachInfo, opts?: { focus?: boolean }): void {
     let conn = this.cache.get(id);
     if (conn) {
       this.cache.delete(id);
@@ -93,9 +93,9 @@ export class ConnectionPool {
     }
     if (conn.el.parentElement !== pane) {
       pane.replaceChildren(conn.el);
-      conn.onMount();
+      conn.onMount(opts);
     } else if (!this.mounted.has(id)) {
-      conn.onMount();
+      conn.onMount(opts);
     }
     this.mounted.add(id);
     this.evict();
@@ -114,13 +114,17 @@ export class ConnectionPool {
   /**
    * Reconcile the visible set to exactly `entries` (in render order): park any
    * mounted session not listed, mount/refresh each listed one in its pane.
+   * `focus: false` shows the panes without taking the keyboard (preview).
    */
-  setVisible(entries: { id: Uuid; pane: HTMLElement; info?: AttachInfo }[]): void {
+  setVisible(
+    entries: { id: Uuid; pane: HTMLElement; info?: AttachInfo }[],
+    opts?: { focus?: boolean },
+  ): void {
     const next = new Set(entries.map((e) => e.id));
     for (const id of [...this.mounted]) {
       if (!next.has(id)) this.unmount(id);
     }
-    for (const e of entries) this.mount(e.id, e.pane, e.info);
+    for (const e of entries) this.mount(e.id, e.pane, e.info, opts);
   }
 
   /** Also tells the daemon which pane is focused (docs/SIDEBAR.md's

web/src/debug.ts

@@ -2,6 +2,8 @@
 // survives reloads, flipped by a keybind (Ctrl+Shift+D), and force-enabled by
 // `?hud` in dev. A `maestro-hud-toggle` event lets the HUD re-render on change.
 
+import { CommandSet, defineCommands } from "./commands.js";
+
 const STORAGE_KEY = "maestro:hud";
 export const HUD_TOGGLE_EVENT = "maestro-hud-toggle";
 
@@ -31,12 +33,9 @@ export function toggleHud(): void {
   setHudEnabled(!isHudEnabled());
 }
 
+const hudKeys = new CommandSet(defineCommands({ "debug.toggleHud": () => toggleHud() }));
+
 /** Global keybind: Ctrl+Shift+D toggles the debug HUD. */
 export function installHudKeybind(): void {
-  window.addEventListener("keydown", (e) => {
-    if (e.ctrlKey && e.shiftKey && (e.key === "D" || e.key === "d")) {
-      e.preventDefault();
-      toggleHud();
-    }
-  });
+  window.addEventListener("keydown", (e) => hudKeys.handle(e));
 }

web/src/help.test.ts

@@ -1,14 +1,8 @@
 // @vitest-environment happy-dom
 import { afterEach, beforeEach, describe, expect, it } from "vitest";
 
-import {
-  SHORTCUTS,
-  closeHelp,
-  installHelpKeybind,
-  isHelpOpen,
-  isTypingTarget,
-  openHelp,
-} from "./help.js";
+import { keyCaps, publishedCommands } from "./commands.js";
+import { closeHelp, groupedCommands, installHelpKeybind, isHelpOpen, openHelp } from "./help.js";
 
 beforeEach(() => {
   installHelpKeybind();
@@ -30,14 +24,24 @@ function rows(): string[] {
 }
 
 describe("help overlay", () => {
-  it("renders every registered shortcut, grouped", () => {
+  it("renders exactly the commands the registry has bound, grouped", () => {
     openHelp();
-    const groups = [...document.querySelectorAll(".help-group-title")].map((h) => h.textContent);
-    expect(groups).toEqual(SHORTCUTS.map((g) => g.title));
-    expect(rows()).toEqual(SHORTCUTS.flatMap((g) => g.items.map((s) => s.keys.join(" "))));
-    expect(document.querySelectorAll(".help-desc")).toHaveLength(
-      SHORTCUTS.reduce((n, g) => n + g.items.length, 0),
+    const groups = groupedCommands();
+    expect([...document.querySelectorAll(".help-group-title")].map((h) => h.textContent)).toEqual(
+      groups.map((g) => g.title),
     );
+    expect(rows()).toEqual(
+      groups.flatMap((g) => g.items.map((c) => keyCaps(c.keys[0]).join(" "))),
+    );
+    expect([...document.querySelectorAll(".help-desc")].map((d) => d.textContent)).toEqual(
+      groups.flatMap((g) => g.items.map((c) => c.label)),
+    );
+  });
+
+  it("names each row by its command id, so a row can't drift from its command", () => {
+    openHelp();
+    expect([...document.querySelectorAll<HTMLElement>(".help-row")].map((r) => r.dataset.commandId))
+      .toEqual(publishedCommands().map((c) => c.id));
   });
 
   it("opens on ? and closes on a second ?", () => {
@@ -94,19 +98,3 @@ describe("help overlay", () => {
     expect(document.querySelectorAll(".help-overlay")).toHaveLength(1);
   });
 });
-
-describe("isTypingTarget", () => {
-  it("is true for form fields and editable nodes, false otherwise", () => {
-    const el = (html: string) => {
-      const d = document.createElement("div");
-      d.innerHTML = html;
-      return d.firstElementChild as HTMLElement;
-    };
-    expect(isTypingTarget(el("<input>"))).toBe(true);
-    expect(isTypingTarget(el("<textarea></textarea>"))).toBe(true);
-    expect(isTypingTarget(el("<select></select>"))).toBe(true);
-    expect(isTypingTarget(el('<div contenteditable="true"></div>'))).toBe(true);
-    expect(isTypingTarget(el("<button></button>"))).toBe(false);
-    expect(isTypingTarget(null)).toBe(false);
-  });
-});

web/src/help.ts

@@ -1,66 +1,15 @@
 /** Keyboard-shortcut overlay (`?`), the web counterpart of the TUI's help
- *  overlay. One registry drives both the rendering and what we claim is bound,
- *  so a binding added to `main.ts` without an entry here reads as missing. */
+ *  overlay. It renders the command registry (`commands.ts`) — the same list
+ *  that dispatches the keys — so a binding can never be documented as one
+ *  thing and do another. */
 
-export interface Shortcut {
-  /** Keycaps, rendered left to right as separate <kbd>. */
-  keys: string[];
-  description: string;
-}
-
-export interface ShortcutGroup {
-  title: string;
-  items: Shortcut[];
-}
-
-export const SHORTCUTS: ShortcutGroup[] = [
-  {
-    title: "Sessions",
-    items: [
-      { keys: ["n"], description: "Open the spawn form" },
-      { keys: ["N"], description: "Spawn a session with every default resolved" },
-    ],
-  },
-  {
-    title: "Session list",
-    items: [
-      {
-        keys: ["Ctrl", "Shift", "H"],
-        description: "Move the keyboard between the session list and the pane",
-      },
-      { keys: ["j"], description: "Highlight the next session" },
-      { keys: ["k"], description: "Highlight the previous session" },
-      { keys: ["Enter"], description: "Open the highlighted session, or expand a folder" },
-      { keys: ["Tab"], description: "Send the keyboard to the pane" },
-      { keys: ["Esc"], description: "Hand the keyboard back to the session list, from the pane" },
-    ],
-  },
-  {
-    title: "Help",
-    items: [
-      { keys: ["?"], description: "Show or hide this help" },
-      { keys: ["Esc"], description: "Close the help overlay or an open menu" },
-    ],
-  },
-  {
-    title: "Debug",
-    items: [{ keys: ["Ctrl", "Shift", "D"], description: "Toggle the debug HUD" }],
-  },
-];
-
-/** True when the event target swallows plain keystrokes — a form field, or the
- *  hidden textarea xterm types into. Shared with `main.ts` so every global
- *  single-key binding is deaf in the same places. */
-export function isTypingTarget(target: EventTarget | null): boolean {
-  const el = target as HTMLElement | null;
-  if (!el || typeof el.tagName !== "string") return false;
-  return (
-    el.tagName === "INPUT" ||
-    el.tagName === "TEXTAREA" ||
-    el.tagName === "SELECT" ||
-    el.isContentEditable
-  );
-}
+import {
+  CommandSet,
+  defineCommands,
+  keyCaps,
+  publishedCommands,
+  type Command,
+} from "./commands.js";
 
 let open: { el: HTMLElement; dispose: () => void } | null = null;
 
@@ -105,7 +54,7 @@ export function openHelp(): HTMLElement {
   head.append(title, close);
   panel.appendChild(head);
 
-  for (const group of SHORTCUTS) {
+  for (const group of groupedCommands()) {
     const section = document.createElement("section");
     section.className = "help-group";
     const heading = document.createElement("h3");
@@ -113,19 +62,20 @@ export function openHelp(): HTMLElement {
     heading.textContent = group.title;
     const list = document.createElement("dl");
     list.className = "help-list";
-    for (const item of group.items) {
+    for (const cmd of group.items) {
       const row = document.createElement("div");
       row.className = "help-row";
+      row.dataset.commandId = cmd.id;
       const keys = document.createElement("dt");
       keys.className = "help-keys";
-      for (const key of item.keys) {
+      for (const key of keyCaps(cmd.keys[0])) {
         const cap = document.createElement("kbd");
         cap.textContent = key;
         keys.appendChild(cap);
       }
       const desc = document.createElement("dd");
       desc.className = "help-desc";
-      desc.textContent = item.description;
+      desc.textContent = cmd.label;
       row.append(keys, desc);
       list.appendChild(row);
     }
@@ -150,6 +100,26 @@ export function openHelp(): HTMLElement {
   return el;
 }
 
+/** The registry's commands, in registry order, bucketed into the help
+ *  overlay's sections. Groups appear in the order their first command does. */
+export function groupedCommands(): { title: string; items: Command[] }[] {
+  const groups: { title: string; items: Command[] }[] = [];
+  for (const cmd of publishedCommands()) {
+    let group = groups.find((g) => g.title === cmd.group);
+    if (!group) {
+      group = { title: cmd.group, items: [] };
+      groups.push(group);
+    }
+    group.items.push(cmd);
+  }
+  return groups;
+}
+
+// The overlay's own two commands. `help.close` is `overlay`-scoped: it is only
+// fed keys while the dialog is up.
+const helpKeys = new CommandSet(defineCommands({ "help.toggle": () => toggleHelp() }));
+const overlayKeys = new CommandSet(defineCommands({ "help.close": () => closeHelp() }));
+
 let installed = false;
 
 /** Global keybind: `?` toggles the overlay, Escape closes it. Idempotent, so a
@@ -158,16 +128,7 @@ export function installHelpKeybind(): void {
   if (installed) return;
   installed = true;
   window.addEventListener("keydown", (e) => {
-    if (e.key === "Escape" && open) {
-      e.preventDefault();
-      closeHelp();
-      return;
-    }
-    // Shift is how `?` is typed on most layouts; the others would be a
-    // different binding entirely.
-    if (e.key !== "?" || e.ctrlKey || e.altKey || e.metaKey) return;
-    if (isTypingTarget(e.target)) return;
-    e.preventDefault();
-    toggleHelp();
+    if (open && overlayKeys.handle(e)) return;
+    helpKeys.handle(e);
   });
 }

web/src/main.ts

@@ -6,7 +6,8 @@ import { renderSidebar } from "./catalog.js";
 import { ConnectionPool } from "./connections.js";
 import { installDrawer, installDrawerSwipe, requestToggleDrawer } from "./drawer.js";
 import { installHudKeybind } from "./debug.js";
-import { installHelpKeybind, isHelpOpen, isTypingTarget } from "./help.js";
+import { installHelpKeybind, isHelpOpen } from "./help.js";
+import { CommandSet, DEFAULT_LEADER, defineCommands } from "./commands.js";
 import { DaemonLink } from "./daemonLink.js";
 import { CatalogStore } from "./events.js";
 import { installRestartOverlay } from "./restartOverlay.js";
@@ -29,6 +30,7 @@ import { mountHud, type Hud } from "./hud.js";
 import { emptyLayout, type Layout, openSessions } from "./layout.js";
 import { createMultiView, type MultiView } from "./multiview.js";
 import { loadLayout, saveLayout } from "./persistence.js";
+import { createPreviewSchedule } from "./previewSchedule.js";
 import {
   FOCUS_PANE_EVENT,
   FOCUS_SIDEBAR_EVENT,
@@ -104,9 +106,20 @@ shellEl.dataset.route = "catalog";
 // after the welcome renderer). The hook only fires on user interaction, by which
 // point `mv` is assigned.
 let mv: MultiView;
+
+// Preview timing (docs/PREVIEW.md): the first move shows at once, and a burst
+// — j held down, or the pointer sweeping the whole list — is coalesced so it
+// costs a couple of pane mounts instead of one per row walked.
+const schedulePreview = createPreviewSchedule((sessionId) => {
+  ensureMultiView();
+  mv?.previewSession(sessionId);
+  updateShellRoute();
+});
+
 const sidebar = renderSidebar(store, {
   onLeafDrag: (id, e) => mv?.beginSessionDrag(id, e),
   link,
+  onPreview: schedulePreview,
 });
 const content = document.createElement("section");
 content.className = "content";
@@ -184,7 +197,9 @@ function infoFor(sessionId: string) {
 
 /** Drive the shell's responsive layout off whether any pane is open. */
 function updateShellRoute(): void {
-  const hasPanes = openSessions(layout).size > 0;
+  // A preview is not an open pane (docs/PREVIEW.md), so the mobile shell does
+  // not swap the list out for a terminal on the way past a row.
+  const hasPanes = (mv?.openSessions() ?? openSessions(layout)).size > 0;
   shellEl.dataset.route = hasPanes ? "attach" : "catalog";
 }
 
@@ -244,11 +259,18 @@ mv = createMultiView({
   onLayoutChange: scheduleSave,
 });
 let contentShowsMv = false;
-function showMultiView(): void {
+/** Put the multi-view in the content pane, without rendering it. A preview
+ *  renders once, on its own terms (`docs/PREVIEW.md`); a render here would
+ *  first re-mount the pane it is about to replace, and that mount takes the
+ *  keyboard away from the list being walked. */
+function ensureMultiView(): void {
   if (!contentShowsMv) {
     content.replaceChildren(mv.el);
     contentShowsMv = true;
   }
+}
+function showMultiView(): void {
+  ensureMultiView();
   mv.render();
   updateShellRoute();
 }
@@ -340,42 +362,59 @@ async function requestFastForward(): Promise<void> {
   });
 }
 
-// Keyboard pair (#67): `n` opens the spawn modal, `N` fast-forwards a spawn.
-// Ignored while typing anywhere (form fields, the terminal's hidden
-// textarea, search) so an attached session's keys are never hijacked.
-document.addEventListener("keydown", (e) => {
-  if (e.ctrlKey || e.altKey || e.metaKey) return;
-  if (isTypingTarget(e.target)) return;
-  // The help overlay owns the keyboard while it is up.
-  if (isHelpOpen()) return;
-  if (e.key === "n") {
-    e.preventDefault();
-    requestOpenSpawn();
-  } else if (e.key === "N") {
-    e.preventDefault();
-    void requestFastForward();
-  }
-});
+// The global half of the command registry (#148). Two sets, because they
+// differ in one thing: the help overlay owns the keyboard while it is up, so
+// the plain keys go deaf behind it while the focus chord does not — an
+// attached terminal must never be able to trap the focus keys.
+//
+// `n` opens the spawn modal, `N` fast-forwards a spawn (#67). Both are plain
+// keys, so `isTypingTarget` keeps them out of form fields and the terminal's
+// hidden textarea.
+const spawnKeys = new CommandSet(
+  defineCommands({
+    "spawn.open": () => requestOpenSpawn(),
+    "spawn.fastForward": () => void requestFastForward(),
+  }),
+);
 
 // Ctrl+Shift+H moves the keyboard between the session list and the pane, the
 // web counterpart of the TUI's `ctrl-w h`. It has to be a chord: an attached
 // terminal owns every plain keystroke, so nothing unmodified could ever get
 // the focus back out of it.
+//
+// This set also owns the leader (`ctrl-a`, the TUI's default): it holds the
+// key as a partial chord and takes select-all off it, so the escape hatch
+// docs/COMMAND-BAR.md describes has somewhere to land (#149).
+const focusKeys = new CommandSet(
+  defineCommands({
+    "focus.toggle": () => {
+      if (sidebar.hasListFocus()) {
+        pool.focusTerminal();
+      } else {
+        drawer.open(); // no-op on desktop; on mobile the list is off-canvas
+        sidebar.focusList();
+      }
+    },
+  }),
+  { leader: DEFAULT_LEADER },
+);
+
 window.addEventListener("keydown", (e) => {
-  if (!e.ctrlKey || !e.shiftKey || e.altKey || e.metaKey) return;
-  if (e.key !== "H" && e.key !== "h") return;
-  e.preventDefault();
-  if (sidebar.hasListFocus()) {
-    pool.focusTerminal();
-  } else {
-    drawer.open(); // no-op on desktop; on mobile the list is off-canvas
-    sidebar.focusList();
-  }
+  if (focusKeys.handle(e)) return;
+  // The help overlay owns the keyboard while it is up.
+  if (isHelpOpen()) return;
+  spawnKeys.handle(e);
 });
 
 // Tab in the session list hands the keyboard to the pane; Escape in the pane
 // hands it back — the pair the TUI gets from `tab` and `esc`.
-document.addEventListener(FOCUS_PANE_EVENT, () => pool.focusTerminal());
+document.addEventListener(FOCUS_PANE_EVENT, () => {
+  // Handing the keyboard to a previewed pane is choosing it: the preview stops
+  // being provisional rather than snapping back the moment the list blurs.
+  const previewed = mv.previewedSessionId();
+  if (previewed) focusSession(previewed);
+  pool.focusTerminal();
+});
 document.addEventListener(FOCUS_SIDEBAR_EVENT, () => {
   drawer.open(); // no-op on desktop; on mobile the list is off-canvas
   sidebar.focusList();
@@ -386,6 +425,7 @@ document.addEventListener(FOCUS_SIDEBAR_EVENT, () => {
  *  on `hashchange` alone — a split or drag can move focus without the hash
  *  changing, leaving a click back onto that session's row silently ignored. */
 function focusSession(sessionId: string): void {
+  schedulePreview.cancel();
   showMultiView();
   mv.openSession(sessionId);
   updateShellRoute();

web/src/multiview.ts

@@ -11,6 +11,7 @@ import {
   addTab,
   closeTab,
   findLeaf,
+  freshId,
   type Dir,
   type Layout,
   leaves,
@@ -19,6 +20,7 @@ import {
   openSessions,
   removeLeaf,
   splitLeaf,
+  type Tab,
 } from "./layout.js";
 import type { AttachInfo } from "./attach.js";
 
@@ -57,11 +59,22 @@ export interface MultiView {
   /** Rebuild the view from the current layout. */
   render: () => void;
   focusedSessionId: () => string | null;
+  /** Show `sessionId` in the content pane without committing to it
+   *  (docs/PREVIEW.md): the tab holding it is brought forward, or a throwaway
+   *  tab carries it. `null` puts back whatever was on screen before. */
+  previewSession: (sessionId: string | null) => void;
+  /** The session being previewed, or null. */
+  previewedSessionId: () => string | null;
 }
 
 export function createMultiView(opts: MultiViewOptions): MultiView {
   const { pool, layout, sidebar, infoFor, onDisconnect, renderWelcome } = opts;
-  const persist = () => opts.onLayoutChange?.();
+  // A preview must never reach localStorage: it is undone the moment the
+  // highlight moves on, and the layout it would save is not the operator's.
+  const persist = () => {
+    if (preview) return;
+    opts.onLayoutChange?.();
+  };
 
   const el = document.createElement("div");
   el.className = "mv";
@@ -83,8 +96,119 @@ export function createMultiView(opts: MultiViewOptions): MultiView {
     render();
   });
 
+  // ---- preview (docs/PREVIEW.md) ----
+  // A preview is a temporary *view* change, never a layout change: it records
+  // exactly what it moved so ending it puts the layout back byte for byte, and
+  // it neither persists nor reports pane focus to the daemon while it is up.
+  interface Preview {
+    sessionId: string;
+    /** Tab that was active before the preview. */
+    prevActiveTabId: string;
+    /** Focused leaf to restore, when the preview stole focus in a real tab. */
+    prevFocus: { tabId: string; leafId: string | null } | null;
+    /** Throwaway tab built for a session that no pane was showing. */
+    tempTabId: string | null;
+  }
+  let preview: Preview | null = null;
+  /// Set while a preview-driven render runs: ending a preview re-mounts the
+  /// pane that was there, and that mount must not pull the keyboard out of the
+  /// sidebar the operator is still walking.
+  let quietRender = false;
+
+  /** Render without any mount taking the keyboard. */
+  function renderQuietly(): void {
+    quietRender = true;
+    try {
+      render();
+    } finally {
+      quietRender = false;
+    }
+  }
+
+  const isTempTab = (tabId: string) => preview?.tempTabId === tabId;
+
+  /** Undo the preview's moves. Mutates only — the caller renders. */
+  function restorePreview(): boolean {
+    const p = preview;
+    if (!p) return false;
+    preview = null;
+    if (p.tempTabId) {
+      const i = layout.tabs.findIndex((t) => t.id === p.tempTabId);
+      if (i >= 0) layout.tabs.splice(i, 1);
+    } else if (p.prevFocus) {
+      const t = layout.tabs.find((x) => x.id === p.prevFocus!.tabId);
+      if (t) t.focusedLeafId = p.prevFocus.leafId;
+    }
+    layout.activeTabId = layout.tabs.some((t) => t.id === p.prevActiveTabId)
+      ? p.prevActiveTabId
+      : layout.tabs[0].id;
+    return true;
+  }
+
+  /** Keep what the preview is showing: its throwaway tab becomes a real one,
+   *  and the focus it moved stands. Returns true when `sessionId` was the
+   *  session being previewed; any other preview is simply discarded. */
+  function settlePreview(sessionId: string): boolean {
+    const p = preview;
+    if (!p) return false;
+    if (p.sessionId !== sessionId) {
+      restorePreview();
+      return false;
+    }
+    preview = null;
+    if (p.tempTabId) {
+      const t = layout.tabs.find((x) => x.id === p.tempTabId);
+      if (t) t.title = `Tab ${layout.tabs.length}`;
+    }
+    return true;
+  }
+
+  function previewSession(sessionId: string | null): void {
+    if (preview?.sessionId === sessionId) return;
+    if (sessionId === null) {
+      if (restorePreview()) renderQuietly();
+      return;
+    }
+    restorePreview();
+    const prevActiveTabId = layout.activeTabId;
+    const loc = locateSession(layout, sessionId);
+    if (loc) {
+      preview = {
+        sessionId,
+        prevActiveTabId,
+        prevFocus: { tabId: loc.tab.id, leafId: loc.tab.focusedLeafId },
+        tempTabId: null,
+      };
+      layout.activeTabId = loc.tab.id;
+      loc.tab.focusedLeafId = loc.leaf.id;
+    } else {
+      // Not on screen anywhere: a throwaway tab carries it, so no existing
+      // pane is evicted and nothing the operator arranged moves.
+      const tab: Tab = { id: freshId("t"), title: "Preview", root: null, focusedLeafId: null };
+      tab.focusedLeafId = splitLeaf(tab, "", sessionId, "row", true);
+      layout.tabs.push(tab);
+      layout.activeTabId = tab.id;
+      preview = { sessionId, prevActiveTabId, prevFocus: null, tempTabId: tab.id };
+    }
+    renderQuietly();
+  }
+
+  /** Any user action that changes the layout for real ends the preview first,
+   *  so it never bakes a throwaway tab into the arrangement. */
+  function dropPreview(): void {
+    restorePreview();
+  }
+
   // ---- highlight helpers ----
 
+  /** Sessions the operator actually has open — the preview's throwaway tab
+   *  does not count, or hovering the sidebar would flip the shell's route. */
+  function realOpenSessions(): Set<string> {
+    const out = openSessions(layout);
+    if (preview?.tempTabId) out.delete(preview.sessionId);
+    return out;
+  }
+
   function focusedLeafSession(): string | null {
     const tab = activeTab(layout);
     const fl = tab.focusedLeafId ? findLeaf(tab.root, tab.focusedLeafId) : null;
@@ -98,9 +222,11 @@ export function createMultiView(opts: MultiViewOptions): MultiView {
     for (const pane of canvas.querySelectorAll<HTMLElement>(".mv-pane")) {
       pane.classList.toggle("is-focused", pane.dataset.leafId === tab.focusedLeafId);
     }
-    pool.setFocus(focusedLeafSession());
+    // A preview is not a focused pane: reporting it would clear the session's
+    // `AwaitingInput` glow just because the operator scrolled past it.
+    if (!preview) pool.setFocus(focusedLeafSession());
     sidebar.setHighlights({
-      open: openSessions(layout),
+      open: realOpenSessions(),
       focused: focusedLeafSession(),
     });
   }
@@ -168,6 +294,11 @@ export function createMultiView(opts: MultiViewOptions): MultiView {
     pane.addEventListener(
       "pointerdown",
       (e) => {
+        // Clicking into a previewed pane is the operator choosing it.
+        if (preview && leaf.sessionId === preview.sessionId) {
+          settlePreview(leaf.sessionId);
+          persist();
+        }
         focusLeaf(leaf.id);
         // Drag a pane by its title bar (desktop only — no docking on mobile).
         if (isMobile) return;
@@ -252,24 +383,31 @@ export function createMultiView(opts: MultiViewOptions): MultiView {
     for (const t of layout.tabs) {
       const tab = document.createElement("button");
       tab.type = "button";
-      tab.className = "mv-tab" + (t.id === layout.activeTabId ? " is-active" : "");
+      tab.className =
+        "mv-tab" +
+        (t.id === layout.activeTabId ? " is-active" : "") +
+        (isTempTab(t.id) ? " is-preview" : "");
       const n = leaves(t.root).filter((l) => l.sessionId).length;
       const label = document.createElement("span");
       label.textContent = t.title + (n ? ` · ${n}` : "");
       tab.appendChild(label);
       tab.addEventListener("click", () => {
+        if (isTempTab(t.id)) return; // a preview tab is not a place to go
+        dropPreview();
         if (layout.activeTabId !== t.id) {
           layout.activeTabId = t.id;
-          render();
         }
+        render();
       });
-      if (layout.tabs.length > 1) {
+      // A preview tab is not the operator's to close: it goes on its own.
+      if (layout.tabs.length > 1 && !isTempTab(t.id)) {
         const close = document.createElement("span");
         close.className = "mv-tab-close";
         close.textContent = "✕";
         close.title = "Close tab";
         close.addEventListener("click", (e) => {
           e.stopPropagation();
+          dropPreview();
           closeTab(layout, t.id);
           render();
         });
@@ -283,6 +421,7 @@ export function createMultiView(opts: MultiViewOptions): MultiView {
     add.textContent = "+";
     add.title = "New tab";
     add.addEventListener("click", () => {
+      dropPreview();
       addTab(layout);
       render();
     });
@@ -292,12 +431,14 @@ export function createMultiView(opts: MultiViewOptions): MultiView {
   // ---- mutations ----
 
   function splitFocused(leafId: string, dir: Dir): void {
+    dropPreview();
     const tab = activeTab(layout);
     tab.focusedLeafId = splitLeaf(tab, leafId, null, dir, true);
     render();
   }
 
   function closePane(leafId: string): void {
+    dropPreview();
     const tab = activeTab(layout);
     removeLeaf(tab, leafId);
     if (tab.focusedLeafId === leafId) {
@@ -307,6 +448,12 @@ export function createMultiView(opts: MultiViewOptions): MultiView {
   }
 
   function openSession(sessionId: string): void {
+    // Opening what is already previewed keeps exactly what is on screen: the
+    // throwaway tab becomes a real one instead of the session moving again.
+    if (settlePreview(sessionId)) {
+      render();
+      return;
+    }
     const loc = locateSession(layout, sessionId);
     if (loc) {
       layout.activeTabId = loc.tab.id;
@@ -337,6 +484,11 @@ export function createMultiView(opts: MultiViewOptions): MultiView {
   /// (#67 review). `newTab` opens its own tab instead of halving whatever the
   /// operator was reading (#100) — what the Spawn button asks for.
   function openSessionBeside(sessionId: string, placement?: { newTab?: boolean }): void {
+    if (settlePreview(sessionId)) {
+      render();
+      opts.onOpenSessionsChange?.();
+      return;
+    }
     const loc = locateSession(layout, sessionId);
     if (loc) {
       layout.activeTabId = loc.tab.id;
@@ -384,13 +536,19 @@ export function createMultiView(opts: MultiViewOptions): MultiView {
     // A lone tab has nothing to switch between, so the bar is only a strip of
     // chrome; CSS hides it until a second tab exists. Spawning still opens its
     // own tab (#100), which brings the bar back with the "+" button on it.
-    el.classList.toggle("mv-solo-tab", layout.tabs.length === 1);
+    // The preview's throwaway tab must not make the bar appear and vanish as
+    // the highlight moves, so it does not count towards "one tab only".
+    el.classList.toggle(
+      "mv-solo-tab",
+      layout.tabs.filter((t) => !isTempTab(t.id)).length === 1,
+    );
+    el.classList.toggle("mv-previewing", preview !== null);
 
     if (!tab.root) {
       pool.setVisible([]);
-      pool.setFocus(null);
+      if (!preview) pool.setFocus(null);
       canvas.appendChild(renderWelcome());
-      sidebar.setHighlights({ open: openSessions(layout), focused: null });
+      sidebar.setHighlights({ open: realOpenSessions(), focused: null });
       persist();
       return;
     }
@@ -408,7 +566,12 @@ export function createMultiView(opts: MultiViewOptions): MultiView {
 
     const hosts: { id: string; host: HTMLElement; info?: AttachInfo }[] = [];
     canvas.appendChild(buildTree(tab.root, hosts));
-    pool.setVisible(hosts.map((h) => ({ id: h.id, pane: h.host, info: h.info })));
+    // A preview keeps the keyboard in the sidebar: mounting must not focus the
+    // terminal, or j/k would stop walking the list after the first step.
+    pool.setVisible(
+      hosts.map((h) => ({ id: h.id, pane: h.host, info: h.info })),
+      { focus: !preview && !quietRender },
+    );
     syncFocus();
     persist();
   }
@@ -431,12 +594,14 @@ export function createMultiView(opts: MultiViewOptions): MultiView {
     // Only the focused leaf's session is live on mobile; the rest park.
     pool.setVisible(
       focused.sessionId ? [{ id: focused.sessionId, pane: pane.host, info: infoFor(focused.sessionId) }] : [],
+      { focus: !preview && !quietRender },
     );
-    pool.setFocus(focused.sessionId ?? null);
-    sidebar.setHighlights({ open: openSessions(layout), focused: focused.sessionId ?? null });
+    if (!preview) pool.setFocus(focused.sessionId ?? null);
+    sidebar.setHighlights({ open: realOpenSessions(), focused: focused.sessionId ?? null });
   }
 
   function closeSession(sessionId: string): void {
+    dropPreview();
     const loc = locateSession(layout, sessionId);
     if (!loc) return;
     removeLeaf(loc.tab, loc.leaf.id);
@@ -628,6 +793,7 @@ export function createMultiView(opts: MultiViewOptions): MultiView {
   }
 
   function beginSessionDrag(sessionId: string, e: PointerEvent): void {
+    dropPreview();
     runDrag({ kind: "session", sessionId }, e, { deferred: true });
   }
 
@@ -636,9 +802,11 @@ export function createMultiView(opts: MultiViewOptions): MultiView {
     openSession,
     openSessionBeside,
     closeSession,
-    openSessions: () => openSessions(layout),
+    openSessions: realOpenSessions,
     beginSessionDrag,
     render,
     focusedSessionId: focusedLeafSession,
+    previewSession,
+    previewedSessionId: () => preview?.sessionId ?? null,
   };
 }

web/src/preview.test.ts

@@ -0,0 +1,218 @@
+// @vitest-environment happy-dom
+// Sidebar preview (docs/PREVIEW.md): highlighting a session shows it in the
+// content pane without changing the layout the operator built.
+import { afterEach, beforeEach, describe, expect, it, vi } from "vitest";
+
+import { addTab, emptyLayout, type Layout, splitLeaf } from "./layout.js";
+import { serializeLayout } from "./persistence.js";
+import { createMultiView, type MultiView } from "./multiview.js";
+import type { ConnectionPool } from "./connections.js";
+import type { SidebarHandle } from "./catalog.js";
+
+function stubFetch(): void {
+  vi.stubGlobal(
+    "fetch",
+    vi.fn(async (input: RequestInfo | URL) => {
+      const url = String(input);
+      const body = url.includes("/api/info")
+        ? { hostname: "h", version: "0", home_dir: "/home/user", presets: [] }
+        : undefined;
+      return new Response(JSON.stringify(body), { status: 200 });
+    }),
+  );
+}
+
+interface Spy {
+  pool: ConnectionPool;
+  visible: () => string[];
+  focusCalls: (string | null)[];
+  mountedWithFocus: (boolean | undefined)[];
+}
+
+function fakePool(): Spy {
+  let visible: string[] = [];
+  const focusCalls: (string | null)[] = [];
+  const mountedWithFocus: (boolean | undefined)[] = [];
+  const pool = {
+    setVisible(entries: { id: string }[], opts?: { focus?: boolean }) {
+      visible = entries.map((e) => e.id);
+      mountedWithFocus.push(opts?.focus);
+    },
+    setFocus(id: string | null) {
+      focusCalls.push(id);
+    },
+  } as unknown as ConnectionPool;
+  return { pool, visible: () => visible, focusCalls, mountedWithFocus };
+}
+
+function fakeSidebar(): SidebarHandle {
+  return {
+    el: document.createElement("aside"),
+    setActive() {},
+    setHighlights() {},
+    focusList() {},
+    hasListFocus() {
+      return false;
+    },
+    dispose() {},
+  };
+}
+
+function makeMv(layout: Layout, pool: ConnectionPool, onLayoutChange?: () => void): MultiView {
+  const mv = createMultiView({
+    pool,
+    layout,
+    sidebar: fakeSidebar(),
+    infoFor: () => ({ name: "sess", command: "bash" }),
+    onDisconnect: () => {},
+    renderWelcome: () => document.createElement("div"),
+    onLayoutChange,
+  });
+  document.body.appendChild(mv.el);
+  mv.render();
+  return mv;
+}
+
+/** Tab 1 holds `s1`; tab 2 holds `s2` and is the active one. */
+function twoTabs(): Layout {
+  const layout = emptyLayout();
+  const first = layout.tabs[0];
+  first.focusedLeafId = splitLeaf(first, "", "s1", "row", true);
+  const second = addTab(layout);
+  second.focusedLeafId = splitLeaf(second, "", "s2", "row", true);
+  layout.activeTabId = second.id;
+  return layout;
+}
+
+describe("sidebar preview", () => {
+  beforeEach(() => {
+    stubFetch();
+    document.body.replaceChildren();
+  });
+
+  afterEach(() => {
+    vi.unstubAllGlobals();
+  });
+
+  it("brings a session's own tab forward, then puts the layout back", () => {
+    const layout = twoTabs();
+    const before = serializeLayout(layout);
+    const spy = fakePool();
+    const mv = makeMv(layout, spy.pool);
+
+    mv.previewSession("s1");
+    expect(spy.visible()).toEqual(["s1"]);
+    expect(mv.previewedSessionId()).toBe("s1");
+
+    mv.previewSession(null);
+    expect(spy.visible()).toEqual(["s2"]);
+    expect(mv.previewedSessionId()).toBeNull();
+    expect(serializeLayout(layout)).toEqual(before);
+  });
+
+  it("shows a session no pane holds in a throwaway tab that leaves no trace", () => {
+    const layout = twoTabs();
+    const before = serializeLayout(layout);
+    const spy = fakePool();
+    const mv = makeMv(layout, spy.pool);
+
+    mv.previewSession("s9");
+    expect(spy.visible()).toEqual(["s9"]);
+    expect(layout.tabs).toHaveLength(3);
+    // The throwaway tab is not something the operator has open.
+    expect(mv.openSessions().has("s9")).toBe(false);
+
+    mv.previewSession(null);
+    expect(layout.tabs).toHaveLength(2);
+    expect(serializeLayout(layout)).toEqual(before);
+  });
+
+  it("stepping between previews leaves only the newest one on screen", () => {
+    const layout = twoTabs();
+    const before = serializeLayout(layout);
+    const spy = fakePool();
+    const mv = makeMv(layout, spy.pool);
+
+    mv.previewSession("s9");
+    mv.previewSession("s1");
+    mv.previewSession("s8");
+    expect(spy.visible()).toEqual(["s8"]);
+    expect(layout.tabs).toHaveLength(3);
+
+    mv.previewSession(null);
+    expect(serializeLayout(layout)).toEqual(before);
+  });
+
+  it("opening what is previewed keeps it: the throwaway tab becomes real", () => {
+    const layout = twoTabs();
+    const spy = fakePool();
+    const mv = makeMv(layout, spy.pool);
+
+    mv.previewSession("s9");
+    mv.openSession("s9");
+
+    expect(mv.previewedSessionId()).toBeNull();
+    expect(layout.tabs).toHaveLength(3);
+    expect(mv.openSessions().has("s9")).toBe(true);
+    expect(spy.visible()).toEqual(["s9"]);
+    // Nothing the operator had open was evicted to make room.
+    expect(mv.openSessions().has("s2")).toBe(true);
+  });
+
+  it("never persists, and saves again once the preview is settled", () => {
+    const layout = twoTabs();
+    const spy = fakePool();
+    const saves = vi.fn();
+    const mv = makeMv(layout, spy.pool, saves);
+    saves.mockClear();
+
+    mv.previewSession("s9");
+    expect(saves).not.toHaveBeenCalled();
+
+    mv.previewSession(null);
+    expect(saves).toHaveBeenCalled();
+  });
+
+  it("never reports a previewed pane as focused to the daemon", () => {
+    const layout = twoTabs();
+    const spy = fakePool();
+    const mv = makeMv(layout, spy.pool);
+    spy.focusCalls.length = 0;
+
+    mv.previewSession("s1");
+    mv.previewSession("s9");
+    expect(spy.focusCalls).toEqual([]);
+
+    mv.previewSession(null);
+    expect(spy.focusCalls).toEqual(["s2"]);
+  });
+
+  it("mounts a preview without taking the keyboard", () => {
+    const layout = twoTabs();
+    const spy = fakePool();
+    const mv = makeMv(layout, spy.pool);
+    spy.mountedWithFocus.length = 0;
+
+    mv.previewSession("s1");
+    expect(spy.mountedWithFocus).toEqual([false]);
+
+    mv.openSession("s1");
+    expect(spy.mountedWithFocus.at(-1)).toBe(true);
+  });
+
+  it("keeps the tab bar hidden while a lone tab is previewing", () => {
+    const layout = emptyLayout();
+    const tab = layout.tabs[0];
+    tab.focusedLeafId = splitLeaf(tab, "", "s1", "row", true);
+    const spy = fakePool();
+    const mv = makeMv(layout, spy.pool);
+    expect(mv.el.classList.contains("mv-solo-tab")).toBe(true);
+
+    mv.previewSession("s9");
+    expect(mv.el.classList.contains("mv-solo-tab")).toBe(true);
+    expect(mv.el.classList.contains("mv-previewing")).toBe(true);
+
+    mv.previewSession(null);
+    expect(mv.el.classList.contains("mv-previewing")).toBe(false);
+  });
+});

web/src/previewSchedule.test.ts

@@ -0,0 +1,92 @@
+import { describe, expect, it } from "vitest";
+
+import { createPreviewSchedule, PREVIEW_MIN_GAP_MS } from "./previewSchedule.js";
+
+/** Hand-driven clock + timer queue, so the schedule is asserted without waiting. */
+function harness() {
+  let now = 1_000;
+  const timers = new Map<number, { at: number; fn: () => void }>();
+  let nextHandle = 1;
+  const emitted: (string | null)[] = [];
+
+  const schedule = createPreviewSchedule((id) => emitted.push(id), {
+    now: () => now,
+    setTimer: (fn, ms) => {
+      const h = nextHandle++;
+      timers.set(h, { at: now + ms, fn });
+      return h;
+    },
+    clearTimer: (h) => {
+      timers.delete(h);
+    },
+  });
+
+  /** Advance the clock, firing any timer that comes due. */
+  const advance = (ms: number) => {
+    now += ms;
+    for (const [h, t] of [...timers]) {
+      if (t.at <= now) {
+        timers.delete(h);
+        t.fn();
+      }
+    }
+  };
+
+  return { schedule, emitted, advance };
+}
+
+describe("preview schedule", () => {
+  it("shows the first preview immediately", () => {
+    const { schedule, emitted } = harness();
+    schedule("s1");
+    expect(emitted).toEqual(["s1"]);
+  });
+
+  it("coalesces a burst into one trailing preview", () => {
+    const { schedule, emitted, advance } = harness();
+    // A pointer sweep across the list, or j held down: every row in between
+    // is walked well inside one gap.
+    schedule("s1");
+    schedule("s2");
+    schedule("s3");
+    expect(emitted).toEqual(["s1"]);
+    advance(PREVIEW_MIN_GAP_MS);
+    expect(emitted).toEqual(["s1", "s3"]);
+  });
+
+  it("shows the next preview immediately once the gap has passed", () => {
+    const { schedule, emitted, advance } = harness();
+    schedule("s1");
+    advance(PREVIEW_MIN_GAP_MS);
+    schedule("s2");
+    expect(emitted).toEqual(["s1", "s2"]);
+  });
+
+  it("drops a superseded trailing preview rather than replaying it", () => {
+    const { schedule, emitted, advance } = harness();
+    schedule("s1");
+    schedule("s2");
+    schedule("s1"); // back where we started inside the same gap
+    advance(PREVIEW_MIN_GAP_MS);
+    // s1 is already on screen, so the trailing edge has nothing to do.
+    expect(emitted).toEqual(["s1"]);
+  });
+
+  it("clears through the same gap, so leaving and re-entering does not blink", () => {
+    const { schedule, emitted, advance } = harness();
+    schedule("s1");
+    schedule(null); // pointer crosses the gap between two rows
+    schedule("s2");
+    advance(PREVIEW_MIN_GAP_MS);
+    expect(emitted).toEqual(["s1", "s2"]);
+  });
+
+  it("cancel drops a pending trailing preview", () => {
+    const { schedule, emitted, advance } = harness();
+    schedule("s1");
+    schedule("s2");
+    schedule.cancel();
+    advance(PREVIEW_MIN_GAP_MS);
+    expect(emitted).toEqual(["s1"]);
+  });
+});

web/src/previewSchedule.ts

@@ -0,0 +1,87 @@
+/**
+ * When the content pane follows the sidebar highlight (docs/PREVIEW.md).
+ *
+ * The highlight itself is never scheduled — that is a class on a row and lands
+ * on the same frame as the input. This governs only the pane swap behind it,
+ * which mounts a terminal and, for a session the connection pool isn't already
+ * holding, opens an attach socket the daemon answers with a `tmux capture-pane`.
+ *
+ * A plain debounce would put that cost in front of every preview, including the
+ * one preview the operator actually meant. Instead the first move shows at once
+ * and the rest of a burst is coalesced: walking a list with `j` held down, or
+ * sweeping the pointer from the top of the sidebar to the bottom, costs one
+ * preview at the start and one at the row you stopped on, not one per row.
+ */
+
+/** Shortest gap between two pane swaps. Long enough that a fast walk mounts a
+ *  couple of terminals rather than one per row; short enough that a deliberate
+ *  second move never waits on it. */
+export const PREVIEW_MIN_GAP_MS = 120;
+
+export interface PreviewScheduleDeps {
+  now?: () => number;
+  setTimer?: (fn: () => void, ms: number) => number;
+  clearTimer?: (handle: number) => void;
+  /** Override the gap; tests and callers otherwise take {@link PREVIEW_MIN_GAP_MS}. */
+  minGapMs?: number;
+}
+
+export interface PreviewSchedule {
+  (sessionId: string | null): void;
+  /** Drop a pending trailing preview without showing it. */
+  cancel(): void;
+}
+
+/**
+ * Wrap `show` so it fires on the leading edge and at most once per gap.
+ *
+ * `show` is called with the session to preview, or `null` to put back whatever
+ * the operator actually opened.
+ */
+export function createPreviewSchedule(
+  show: (sessionId: string | null) => void,
+  deps: PreviewScheduleDeps = {},
+): PreviewSchedule {
+  const now = deps.now ?? (() => Date.now());
+  const setTimer = deps.setTimer ?? ((fn, ms) => window.setTimeout(fn, ms));
+  const clearTimer = deps.clearTimer ?? ((h) => window.clearTimeout(h));
+  const minGap = deps.minGapMs ?? PREVIEW_MIN_GAP_MS;
+
+  let lastShownAt = Number.NEGATIVE_INFINITY;
+  let shown: string | null | undefined;
+  let pendingTimer: number | undefined;
+  let pendingId: string | null = null;
+
+  const emit = (id: string | null) => {
+    // Nothing to do when the burst ended on the view already up: re-showing it
+    // would tear down and re-mount the pane for no visible change.
+    if (shown === id) return;
+    shown = id;
+    lastShownAt = now();
+    show(id);
+  };
+
+  const cancelPending = () => {
+    if (pendingTimer === undefined) return;
+    clearTimer(pendingTimer);
+    pendingTimer = undefined;
+  };
+
+  const schedule = ((sessionId: string | null) => {
+    pendingId = sessionId;
+    const waited = now() - lastShownAt;
+    if (waited >= minGap) {
+      cancelPending();
+      emit(sessionId);
+      return;
+    }
+    if (pendingTimer !== undefined) return; // already waiting; `pendingId` wins
+    pendingTimer = setTimer(() => {
+      pendingTimer = undefined;
+      emit(pendingId);
+    }, minGap - waited);
+  }) as PreviewSchedule;
+
+  schedule.cancel = cancelPending;
+  return schedule;
+}

web/src/sidebarNav.test.ts

@@ -39,8 +39,11 @@ const A = "aaaaaaaa-0000-0000-0000-00000000000a";
 const B = "aaaaaaaa-0000-0000-0000-00000000000b";
 
 /** Two sessions in sibling directories: two folder headers, two cards. */
-function twoFolders(): { el: HTMLElement; handle: ReturnType<typeof renderSidebar> } {
-  const handle = renderSidebar(storeWith([session(A, "/one"), session(B, "/two")]));
+function twoFolders(opts: Parameters<typeof renderSidebar>[1] = {}): {
+  el: HTMLElement;
+  handle: ReturnType<typeof renderSidebar>;
+} {
+  const handle = renderSidebar(storeWith([session(A, "/one"), session(B, "/two")]), opts);
   // Mounted: `focusList` moves real DOM focus, which needs a live document.
   document.body.replaceChildren(handle.el);
   return { el: handle.el, handle };
@@ -117,6 +120,43 @@ describe("sidebar keyboard navigation", () => {
     expect(asked).toBe(1);
   });
 
+  it("c collapses and expands the highlighted folder", () => {
+    const { el } = twoFolders();
+    const header = el.querySelectorAll<HTMLElement>(".tree-folder-header")[0];
+    header.click(); // collapse /one, so the walk stops on its header
+
+    press(tree(el), "j");
+    expect(highlighted(el)).toBe("folder:one");
+    press(tree(el), "c");
+    // Expanded: the card it was hiding is back in the walk.
+    expect(el.querySelector(`[data-nav-key="session:${A}"]`)).not.toBeNull();
+  });
+
+  it("r renames the highlighted session in place", () => {
+    const { el } = twoFolders();
+    press(tree(el), "j");
+    press(tree(el), "r");
+    const field = el.querySelector<HTMLInputElement>(".leaf-rename");
+    expect(field).not.toBeNull();
+    // Escape settles the rename, so the module-level "a row is being renamed"
+    // flag doesn't leak into the next test.
+    field!.dispatchEvent(new KeyboardEvent("keydown", { key: "Escape", bubbles: true }));
+  });
+
+  it("x kills the highlighted session", async () => {
+    const { el } = twoFolders();
+    const killed: string[] = [];
+    window.fetch = ((input: RequestInfo | URL, init?: RequestInit) => {
+      killed.push(`${init?.method ?? "GET"} ${String(input)}`);
+      return Promise.resolve(new Response(null, { status: 204 }));
+    }) as typeof window.fetch;
+
+    press(tree(el), "j");
+    press(tree(el), "x");
+    await Promise.resolve();
+    expect(killed.some((r) => r.startsWith("DELETE") && r.includes(A))).toBe(true);
+  });
+
   it("leaves the keyboard alone while a row is being renamed", () => {
     const { el } = twoFolders();
     press(tree(el), "j");
@@ -126,3 +166,40 @@ describe("sidebar keyboard navigation", () => {
     expect(highlighted(el)).toBe(`session:${A}`);
   });
 });
+
+describe("sidebar preview requests (docs/PREVIEW.md)", () => {
+  it("asks for a preview on every keyboard step, and for none once the list blurs", () => {
+    const seen: (string | null)[] = [];
+    const { el } = twoFolders({ onPreview: (id) => seen.push(id) });
+
+    press(tree(el), "j");
+    press(tree(el), "j");
+    expect(seen).toEqual([A, B]);
+
+    tree(el).dispatchEvent(new FocusEvent("blur"));
+    expect(seen.at(-1)).toBe(null);
+  });
+
+  it("asks for a preview of the hovered card, and clears it on the way out", () => {
+    const seen: (string | null)[] = [];
+    const { el } = twoFolders({ onPreview: (id) => seen.push(id) });
+    const card = el.querySelectorAll<HTMLElement>(".tree-leaf")[0];
+
+    card.dispatchEvent(new PointerEvent("pointerover", { bubbles: true, pointerType: "mouse" }));
+    expect(seen).toEqual([A]);
+    // Moving within the same card is not a new preview.
+    card.dispatchEvent(new PointerEvent("pointerover", { bubbles: true, pointerType: "mouse" }));
+    expect(seen).toHaveLength(1);
+
+    tree(el).dispatchEvent(new PointerEvent("pointerleave", { pointerType: "mouse" }));
+    expect(seen.at(-1)).toBe(null);
+  });
+
+  it("ignores touch, where a tap already opens the session", () => {
+    const seen: (string | null)[] = [];
+    const { el } = twoFolders({ onPreview: (id) => seen.push(id) });
+    const card = el.querySelectorAll<HTMLElement>(".tree-leaf")[0];
+    card.dispatchEvent(new PointerEvent("pointerover", { bubbles: true, pointerType: "touch" }));
+    expect(seen).toEqual([]);
+  });
+});

web/src/styles.css

@@ -1064,7 +1064,6 @@ textarea {
   cursor: pointer;
   font-family: var(--font-mono);
   font-size: var(--fs-12);
-  transition: color var(--dur-fast) var(--ease-out);
 }
 
 .tree-folder-header:hover {
@@ -1076,9 +1075,9 @@ textarea {
   text-align: center;
   color: var(--faint);
   font-size: var(--fs-11);
-  transition:
-    transform var(--dur) var(--ease-out),
-    color var(--dur-fast) var(--ease-out);
+  /* The rotation is the collapse animation and stays; the hover colour is
+     immediate, like the row's own hover. */
+  transition: transform var(--dur) var(--ease-out);
 }
 
 .tree-folder-header[aria-expanded="false"] .chevron {
@@ -1115,9 +1114,11 @@ textarea {
   border-radius: var(--r-1);
   color: var(--ink);
   position: relative;
-  transition:
-    background var(--dur-fast) var(--ease-out),
-    box-shadow var(--dur-fast) var(--ease-out);
+  /* No transition on `background`: it is what hover paints, and easing it puts
+     a visible delay between the pointer landing on a row and the row admitting
+     it. The ring (`.is-highlighted`, `.is-active`) still eases — that one
+     follows a keyboard walk, not the pointer. */
+  transition: box-shadow var(--dur-fast) var(--ease-out);
 }
 
 /* "Alive" reads as a faint wash on the row itself — no per-row status icon. */
@@ -2023,6 +2024,51 @@ input.leaf-rename:focus {
   min-height: 0;
 }
 
+/* Mobile: the spawn form is the tallest dialog we have, so it takes the whole
+   screen and lays out as one flex column — header, scrolling body, actions
+   pinned to the bottom edge. Below the fold is where the Submit button used to
+   hide. */
+@media (max-width: 599px) {
+  .modal.spawn-modal {
+    height: 100dvh;
+    max-height: none;
+    border: 0;
+    border-radius: 0;
+  }
+
+  .spawn-modal .spawn-form {
+    flex: 1 1 auto;
+    padding-bottom: 0;
+  }
+
+  /* One scroll box, not four: the pickers' own caps stack scrollable regions
+     inside a screen that is already short. Let them grow and let the form
+     scroll. */
+  .spawn-modal .picker,
+  .spawn-modal .picker.projects,
+  .spawn-modal .picker.wt-choices {
+    max-height: none;
+    overflow-y: visible;
+  }
+
+  /* Rides the bottom of the scroll box: reachable at any scroll position, and
+     `margin-top: auto` keeps it at the screen's foot when the form is short. */
+  .spawn-modal .form-actions {
+    position: sticky;
+    bottom: 0;
+    margin-top: auto;
+    padding: var(--sp-2) 0 calc(var(--sp-2) + env(safe-area-inset-bottom, 0px));
+    background: var(--surface);
+    box-shadow: 0 -8px 12px -8px oklch(0 0 0 / 0.5);
+  }
+
+  .spawn-modal .form-actions .btn {
+    flex: 1 1 0;
+    justify-content: center;
+    min-height: 44px;
+  }
+}
+
 /* ---------- forms ---------- */
 
 .spawn-form {
@@ -2838,6 +2884,38 @@ input.leaf-rename:focus {
   color: var(--ink);
 }
 
+/* Preview (docs/PREVIEW.md): the content pane is showing a session the
+   operator only highlighted, so it reads as provisional — a dashed tab and a
+   dashed inset ring on the canvas — and reverts when the highlight moves. */
+.mv-tab.is-preview {
+  border-style: dashed;
+  font-style: italic;
+}
+.mv.mv-previewing .mv-canvas::before {
+  content: "preview";
+  position: absolute;
+  top: var(--sp-2);
+  right: var(--sp-3);
+  z-index: var(--z-sticky);
+  padding: 1px var(--sp-2);
+  border-radius: var(--r-1);
+  font: 500 var(--fs-11) / 1.5 var(--font-mono);
+  letter-spacing: 0.04em;
+  color: var(--accent-ink);
+  background: var(--accent);
+  opacity: 0.85;
+  pointer-events: none;
+}
+.mv.mv-previewing .mv-canvas::after {
+  content: "";
+  position: absolute;
+  inset: 0;
+  pointer-events: none;
+  border: 1px dashed var(--accent-ring);
+  border-radius: var(--r-1);
+  z-index: var(--z-sticky);
+}
+
 /* canvas + welcome */
 .mv-canvas {
   position: relative;

web/src/webglRenderer.test.ts

@@ -0,0 +1,55 @@
+import { describe, expect, it, vi } from "vitest";
+
+import { MAX_CONTEXT_LOSSES, WebglPolicy } from "./webglRenderer.js";
+
+describe("WebglPolicy", () => {
+  it("is enabled when the browser supports WebGL2", () => {
+    expect(new WebglPolicy(() => true).enabled()).toBe(true);
+  });
+
+  it("is disabled when the browser has no WebGL2", () => {
+    expect(new WebglPolicy(() => false).enabled()).toBe(false);
+  });
+
+  it("probes only once, however often it is asked", () => {
+    const probe = vi.fn(() => true);
+    const policy = new WebglPolicy(probe);
+    policy.enabled();
+    policy.enabled();
+    policy.enabled();
+    expect(probe).toHaveBeenCalledTimes(1);
+  });
+
+  it("tolerates a loss below the budget — a backgrounded tab is ordinary", () => {
+    const policy = new WebglPolicy(() => true);
+    policy.noteContextLoss();
+    expect(policy.enabled()).toBe(true);
+  });
+
+  it("gives up for good once losses reach the budget", () => {
+    const policy = new WebglPolicy(() => true);
+    for (let i = 0; i < MAX_CONTEXT_LOSSES; i++) policy.noteContextLoss();
+    expect(policy.enabled()).toBe(false);
+    expect(policy.contextLosses()).toBe(MAX_CONTEXT_LOSSES);
+  });
+
+  it("stays disabled past the budget, and never bothers probing", () => {
+    const probe = vi.fn(() => true);
+    const policy = new WebglPolicy(probe);
+    for (let i = 0; i < MAX_CONTEXT_LOSSES + 3; i++) policy.noteContextLoss();
+    expect(policy.enabled()).toBe(false);
+    expect(probe).not.toHaveBeenCalled();
+  });
+
+  it("treats a throwing probe as unsupported", () => {
+    const policy = new WebglPolicy(() => {
+      throw new Error("no gl for you");
+    });
+    expect(() => policy.enabled()).not.toThrow();
+    expect(policy.enabled()).toBe(false);
+  });
+
+  it("reports no WebGL2 under the test DOM, which has no GPU", () => {
+    expect(new WebglPolicy().enabled()).toBe(false);
+  });
+});

web/src/webglRenderer.ts

@@ -0,0 +1,73 @@
+// WebGL renderer policy for attached terminals. Split out of attach.ts so it
+// can be tested without a DOM or an xterm instance (same reasoning as
+// reconnect.ts).
+//
+// xterm's default renderer builds DOM nodes per cell, which is CPU-bound —
+// exactly the wrong bottleneck on a phone, where a full-screen repaint from an
+// agent dumping output visibly stutters. The WebGL addon moves glyph drawing to
+// a GPU texture atlas instead.
+//
+// The cost is that a WebGL context is a scarce, revocable resource:
+//
+//   * Browsers cap live contexts (~16 on desktop Chrome, fewer on Android) and
+//     silently kill the oldest past the cap. `ConnectionPool` keeps MAX_PARKED
+//     parked connections alive on top of the mounted ones, so handing every
+//     connection its own context would blow that budget on its own and bring a
+//     parked terminal back blank.
+//   * Android drops contexts as routine housekeeping — backgrounding the tab,
+//     locking the screen, memory pressure.
+//
+// So the context follows the *view*, not the connection: acquired on mount,
+// released on park. Losses count against a shared budget, because a device that
+// keeps dropping contexts is telling us it cannot sustain one.
+
+/** Context losses tolerated before the page gives up and stays on the DOM
+ *  renderer. One loss is ordinary (a tab switch); repeated losses mean the
+ *  device is thrashing, and re-acquiring only makes it worse. */
+export const MAX_CONTEXT_LOSSES = 2;
+
+/** Can this browser hand out a WebGL2 context at all? */
+export function probeWebgl2(): boolean {
+  return document.createElement("canvas").getContext("webgl2") !== null;
+}
+
+/**
+ * Whether an attached terminal should try the WebGL renderer right now.
+ *
+ * Shared by every connection on the page: the context budget and the "this
+ * device cannot cope" signal are both global, not per-terminal.
+ */
+export class WebglPolicy {
+  private supported: boolean | null = null;
+  private losses = 0;
+
+  constructor(private readonly probe: () => boolean = probeWebgl2) {}
+
+  /** True while WebGL is both available and still worth attempting. The probe
+   *  runs at most once — support does not change under us, and creating
+   *  throwaway contexts to re-ask would itself consume the budget. */
+  enabled(): boolean {
+    if (this.losses >= MAX_CONTEXT_LOSSES) return false;
+    if (this.supported === null) {
+      try {
+        this.supported = this.probe();
+      } catch {
+        // A browser that throws rather than returning null has no usable
+        // context either way.
+        this.supported = false;
+      }
+    }
+    return this.supported;
+  }
+
+  /** Record a lost context. Past the budget, `enabled()` stays false for the
+   *  life of the page. */
+  noteContextLoss(): void {
+    this.losses += 1;
+  }
+
+  /** Losses recorded so far — for the debug HUD and tests. */
+  contextLosses(): number {
+    return this.losses;
+  }
+}