feat(layout): fullscreen + interactive pane resizing

Add a window-management layer so the chat, roster and sandbox-terminal
panes can be resized live and fullscreened, with named presets for
recall.

- New layout.rs: single source of truth for the body split (pty_pct,
  roster_width) and a Zoom state (Normal/Term/Chat), persisted to
  layouts/<slug>.toml like themes. Both ui::draw and app::sbx_dims read
  from it, so resizing just mutates state and clears announced_dims —
  the per-tick loop re-syncs and broadcasts the new PTY grid.
- F4 cycles terminal/chat fullscreen (F-keys aren't forwarded to the
  shell, so nothing is stolen from in-shell apps).
- Interactive editing: click a pane (or F5 to cycle terminal -> chat ->
  roster) to select it; arrows then resize it live, Esc/Enter finishes.
  The selected pane gets a bold accent border and an ✎ title marker.
  ui::pane_at hit-tests against the same body_areas rects draw() paints.
- /layout slimmed to presets only (save/load/list/rm/reset); the old
  numeric pty/chat/roster and full/chatfull/normal verbs are replaced by
  the interactive flow.
- Help menu updated: LAYOUT cluster + KEYS line document F4, click/F5,
  arrows and Esc.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

hh/src/app.rs

@@ -1,6 +1,7 @@
 //! TUI application state, network event model, and the async run loop.
 
 use crate::ft;
+use crate::layout::Layout;
 use crate::net::{self, Session};
 use crate::sbx;
 use crate::theme::Theme;
@@ -10,7 +11,7 @@ use base64::engine::general_purpose::STANDARD;
 use base64::Engine;
 use crossterm::event::{
     DisableMouseCapture, EnableMouseCapture, Event, EventStream, KeyCode, KeyEventKind,
-    KeyModifiers, MouseEventKind,
+    KeyModifiers, MouseButton, MouseEventKind,
 };
 use crossterm::execute;
 use crossterm::terminal::{
@@ -159,6 +160,15 @@ pub struct VboxPicker {
     pub selected: usize,
 }
 
+/// A resizable region of the window, for interactive layout editing. Selected by
+/// clicking it (or cycling with F5); once selected, arrow keys resize it.
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum Pane {
+    Chat,
+    Roster,
+    Terminal,
+}
+
 pub struct App {
     pub me: String,
     pub lines: Vec<ChatLine>,
@@ -211,6 +221,13 @@ pub struct App {
     /// Tracked so the broker Ready handler can re-grant its drive and `/ai stop`
     /// can revoke the right ACL entry.
     pub agent_name: Option<String>,
+    /// Window layout: chat/terminal split, roster width, fullscreen zoom. Read
+    /// by `ui::draw` and `sbx_dims`; mutated by F4/F5 + interactive editing.
+    pub layout: Layout,
+    /// Interactive layout editing: the pane currently selected for resizing
+    /// (click it or cycle with F5), or None when not editing. When set, arrow
+    /// keys resize this pane instead of scrolling.
+    pub focused_pane: Option<Pane>,
 }
 
 impl App {
@@ -244,9 +261,25 @@ impl App {
             spin: 0,
             agent_sbx_allow: false,
             agent_name: None,
+            layout: Layout::default(),
+            focused_pane: None,
         }
     }
 
+    /// Cycle the interactive-edit selection: Terminal → Chat → Roster → off.
+    /// Bound to F5; clicking a pane jumps straight to it instead. The Terminal
+    /// step is skipped when no sandbox is up (nothing to resize there).
+    fn cycle_focus(&mut self) {
+        let has_term = self.sandbox.is_some();
+        self.focused_pane = match self.focused_pane {
+            None if has_term => Some(Pane::Terminal),
+            None => Some(Pane::Chat),
+            Some(Pane::Terminal) => Some(Pane::Chat),
+            Some(Pane::Chat) => Some(Pane::Roster),
+            Some(Pane::Roster) => None,
+        };
+    }
+
     /// Append a chat line. Holds the viewport steady if scrolled up, and caps
     /// the in-memory backlog.
     fn push_line(&mut self, l: ChatLine) {
@@ -463,9 +496,32 @@ impl App {
     }
 }
 
-fn sbx_dims(term_w: u16, term_h: u16) -> (u16, u16) {
+/// Human label for a resizable pane (used in layout-editing hints).
+fn pane_label(p: Pane) -> &'static str {
+    match p {
+        Pane::Chat => "chat",
+        Pane::Roster => "roster",
+        Pane::Terminal => "terminal",
+    }
+}
+
+/// Join saved-preset names for display, or "none" when there are none.
+fn once_or_none(names: Vec<String>) -> String {
+    if names.is_empty() {
+        "none".to_string()
+    } else {
+        names.join(" · ")
+    }
+}
+
+/// PTY grid (rows, cols) for the sandbox terminal. `pty_pct` is the terminal's
+/// share of the body height (see `layout::Layout`); it must match the split
+/// `ui::draw` paints, so they stay in lock-step via `app.layout`. Width is the
+/// full body width — the terminal pane always spans the frame, only its height
+/// changes with the split.
+fn sbx_dims(term_w: u16, term_h: u16, pty_pct: u16) -> (u16, u16) {
     let body_h = term_h.saturating_sub(4);
-    let sbx_h = (body_h as u32 * 55 / 100) as u16;
+    let sbx_h = (body_h as u32 * pty_pct as u32 / 100) as u16;
     (
         sbx_h.saturating_sub(2).max(1),
         term_w.saturating_sub(2).max(1),
@@ -842,6 +898,10 @@ pub async fn run(params: net::ConnParams, mut session: Session, mut theme: Theme
 
     let mut app = App::new(session.username.clone());
     app.password = params.password.clone();
+    // Seed the roster width from the active vestment so a `--theme` with a wider
+    // roster is honoured; from here on the live layout owns it (so /theme swaps
+    // don't stomp a width the user has set with /layout).
+    app.layout.roster_width = theme.roster_width;
     let mut events = EventStream::new();
     let mut tick = tokio::time::interval(Duration::from_millis(50));
 
@@ -863,7 +923,7 @@ pub async fn run(params: net::ConnParams, mut session: Session, mut theme: Theme
 
         if broker.is_some() {
             if let Ok(sz) = term.size() {
-                let dims = sbx_dims(sz.width, sz.height);
+                let dims = sbx_dims(sz.width, sz.height, app.layout.effective_pty_pct());
                 if announced_dims != Some(dims) {
                     announced_dims = Some(dims);
                     if let Some(sb) = &broker {
@@ -1043,6 +1103,64 @@ pub async fn run(params: net::ConnParams, mut session: Session, mut theme: Theme
                             } else {
                                 app.sys("you don't have drive permission — the owner can /grant you");
                             }
+                        } else if k.code == KeyCode::F(4) {
+                            // Fullscreen the terminal (cycle terminal → chat → split).
+                            // Caught before the drive branch so it works mid-session;
+                            // F-keys aren't forwarded to the shell anyway (key_to_pty).
+                            if app.sandbox.is_some() {
+                                app.layout.cycle_zoom();
+                                announced_dims = None; // re-sync PTY to the new height
+                                app.sys(format!("⛧ {}", app.layout.describe()));
+                            } else {
+                                app.sys("no sandbox to fullscreen — /sbx launch first");
+                            }
+                        } else if k.code == KeyCode::F(5) {
+                            // Enter/cycle interactive layout editing: pick a pane to
+                            // resize (Terminal → Chat → Roster → off). Clicking a pane
+                            // selects it directly; arrows then resize it.
+                            app.cycle_focus();
+                            match app.focused_pane {
+                                Some(p) => app.sys(format!(
+                                    "⛧ editing {} — arrows resize · Esc done",
+                                    pane_label(p)
+                                )),
+                                None => app.sys("⛧ layout editing off"),
+                            }
+                        } else if app.focused_pane.is_some() && !app.driving {
+                            // Interactive layout editing: a pane is selected (via click
+                            // or F5). Arrows resize it live; Esc/Enter finishes. Sits
+                            // before the driving branch but is gated on !driving so the
+                            // shell still gets its keys while you hold the PTY.
+                            let pane = app.focused_pane.unwrap();
+                            match (pane, k.code) {
+                                (_, KeyCode::Esc) | (_, KeyCode::Enter) => {
+                                    app.focused_pane = None;
+                                    app.sys(format!("⛧ {}", app.layout.describe()));
+                                }
+                                // Terminal taller / chat shorter (and the mirror image
+                                // when the chat pane is the one selected).
+                                (Pane::Terminal, KeyCode::Up) | (Pane::Chat, KeyCode::Down) => {
+                                    app.layout.grow_pty(3);
+                                    announced_dims = None;
+                                    app.sys(format!("⛧ {}", app.layout.describe()));
+                                }
+                                (Pane::Terminal, KeyCode::Down) | (Pane::Chat, KeyCode::Up) => {
+                                    app.layout.shrink_pty(3);
+                                    announced_dims = None;
+                                    app.sys(format!("⛧ {}", app.layout.describe()));
+                                }
+                                (Pane::Roster, KeyCode::Left) => {
+                                    app.layout.roster_width =
+                                        app.layout.roster_width.saturating_sub(2);
+                                    app.sys(format!("⛧ {}", app.layout.describe()));
+                                }
+                                (Pane::Roster, KeyCode::Right) => {
+                                    app.layout.roster_width =
+                                        (app.layout.roster_width + 2).min(Layout::MAX_ROSTER);
+                                    app.sys(format!("⛧ {}", app.layout.describe()));
+                                }
+                                _ => {} // ignore other keys while editing
+                            }
                         } else if app.driving {
                             // Esc is NOT a release key here — vim & friends need it,
                             // so it's forwarded to the PTY like any other key (see
@@ -1127,6 +1245,27 @@ pub async fn run(params: net::ConnParams, mut session: Session, mut theme: Theme
                                     app.chat_scroll = app.chat_scroll.saturating_sub(3);
                                 }
                             }
+                            // Left-click a pane to select it for interactive resize
+                            // (then arrows adjust it; Esc finishes). Skipped while
+                            // driving the shell or with an overlay up, so clicks there
+                            // don't hijack the terminal/help/picker.
+                            MouseEventKind::Down(MouseButton::Left)
+                                if !app.driving && !app.show_help && app.vbox_picker.is_none() =>
+                            {
+                                if let Ok(sz) = term.size() {
+                                    if let Some(p) =
+                                        ui::pane_at(sz.width, sz.height, &app, m.column, m.row)
+                                    {
+                                        app.focused_pane = Some(p);
+                                        app.sys(format!(
+                                            "⛧ editing {} — arrows resize · Esc done",
+                                            pane_label(p)
+                                        ));
+                                    } else {
+                                        app.focused_pane = None;
+                                    }
+                                }
+                            }
                             _ => {}
                         }
                     }
@@ -1516,6 +1655,73 @@ fn handle_command(
                 )),
             }
         }
+    } else if let Some(rest) = line.strip_prefix("/layout") {
+        // Named layout presets only — live resizing is interactive now (F4
+        // fullscreen, F5 or click a pane then arrows). `/layout` keeps just the
+        // memorable verbs for saving/recalling arrangements, plus `reset`.
+        // Loading a preset clears announced_dims so the run loop re-syncs (and
+        // broadcasts) the live PTY size on the next tick.
+        let rest = rest.trim();
+        let (cmd, arg) = rest
+            .split_once(char::is_whitespace)
+            .map(|(c, a)| (c, a.trim()))
+            .unwrap_or((rest, ""));
+        let mut resized = false;
+        match cmd {
+            "" => {
+                app.sys(format!("⛧ layout: {}", app.layout.describe()));
+                app.sys("  resize live: F4 fullscreen · F5 or click a pane, then arrows · Esc done");
+                app.sys(format!(
+                    "  presets: {} — /layout save <name> · load <name> · rm <name>",
+                    once_or_none(Layout::available())
+                ));
+            }
+            "reset" | "default" => {
+                let roster = app.layout.roster_width;
+                app.layout = Layout::default();
+                app.layout.roster_width = roster; // keep your roster choice on reset
+                resized = true;
+                app.sys(format!("⛧ layout reset — {}", app.layout.describe()));
+            }
+            "save" if !arg.is_empty() => match app.layout.save(arg) {
+                Ok(slug) => app.sys(format!(
+                    "⛧ saved layout '{slug}' — re-apply anytime with /layout load {slug}"
+                )),
+                Err(e) => app.err(format!("couldn't save layout: {e}")),
+            },
+            "load" | "apply" if !arg.is_empty() => match Layout::by_name(arg) {
+                Ok(l) => {
+                    app.layout = l;
+                    resized = true;
+                    app.sys(format!("⛧ loaded layout '{arg}' — {}", app.layout.describe()));
+                }
+                Err(_) => app.err(format!(
+                    "no saved layout '{arg}' — saved: {}",
+                    once_or_none(Layout::available())
+                )),
+            },
+            "list" | "presets" | "ls" => {
+                app.sys(format!("⛧ saved layouts: {}", once_or_none(Layout::available())));
+            }
+            "rm" | "delete" | "del" if !arg.is_empty() => match Layout::remove(arg) {
+                Ok(()) => app.sys(format!("⛧ deleted layout '{arg}'")),
+                Err(e) => app.err(format!("{e}")),
+            },
+            // Bare `/layout <name>` → load a saved preset if it exists.
+            name => match Layout::by_name(name) {
+                Ok(l) => {
+                    app.layout = l;
+                    resized = true;
+                    app.sys(format!("⛧ loaded layout '{name}' — {}", app.layout.describe()));
+                }
+                Err(_) => app.sys(
+                    "usage: /layout [save <name>|load <name>|list|rm <name>|reset] — resize live with F4/F5 or click",
+                ),
+            },
+        }
+        if resized {
+            *announced_dims = None; // force the run loop to re-sync the PTY size
+        }
     } else if line == "/drive" {
         // Mobile-friendly alternative to F2 (no function key needed).
         if app.sandbox.is_none() {
@@ -1656,7 +1862,7 @@ fn handle_command(
                         // install also leaves its daemon up).
                         let install_first = !installed;
                         let sz = term.size().map(|s| (s.width, s.height)).unwrap_or((80, 24));
-                        let (rows, cols) = sbx_dims(sz.0, sz.1);
+                        let (rows, cols) = sbx_dims(sz.0, sz.1, app.layout.effective_pty_pct());
                         *launching = true;
                         let members: Vec<String> =
                             app.users.iter().map(|u| u.username.clone()).collect();
@@ -1762,7 +1968,7 @@ fn handle_command(
                         // (stopped, preserved) instance and re-attaches its shell.
                         let label = label.to_string();
                         let sz = term.size().map(|s| (s.width, s.height)).unwrap_or((80, 24));
-                        let (rows, cols) = sbx_dims(sz.0, sz.1);
+                        let (rows, cols) = sbx_dims(sz.0, sz.1, app.layout.effective_pty_pct());
                         *launching = true;
                         let members: Vec<String> =
                             app.users.iter().map(|u| u.username.clone()).collect();

hh/src/layout.rs

@@ -0,0 +1,239 @@
+//! Window layout ("cell plan"): how the chat, roster and sandbox-terminal panes
+//! divide the screen, plus a fullscreen ("zoom") mode for the terminal or chat.
+//!
+//! The split is a single source of truth shared by `ui::draw` (what's painted)
+//! and `app::sbx_dims` (the PTY grid we resize the real shell to). Because the
+//! run loop re-syncs the PTY every tick, changing these values is all it takes
+//! to live-resize the terminal and broadcast the new dims to the room.
+//!
+//! Named arrangements can be saved to `layouts/<slug>.toml` and re-applied later
+//! with `/layout load <name>`, mirroring how `theme.rs` persists vestments.
+
+use anyhow::Context;
+use serde::{Deserialize, Serialize};
+
+/// Where saved layout presets live (mirrors `theme::THEMES_DIR`).
+pub const LAYOUTS_DIR: &str = concat!(env!("CARGO_MANIFEST_DIR"), "/layouts");
+
+/// Fullscreen state. `Normal` honours the `pty_pct` split; `Term` gives the
+/// whole body to the sandbox terminal (chat + roster hidden); `Chat` hides the
+/// terminal so chat + roster fill the body. The 3-line input bar always stays
+/// visible, so you can always type `/layout normal` or press F4 to get back.
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Serialize, Deserialize)]
+pub enum Zoom {
+    Normal,
+    Term,
+    Chat,
+}
+
+impl Default for Zoom {
+    fn default() -> Self {
+        Zoom::Normal
+    }
+}
+
+#[derive(Debug, Clone, Serialize, Deserialize)]
+#[serde(default)]
+pub struct Layout {
+    /// Sandbox terminal's share of the body height, as a percentage (clamped
+    /// 20–90 so neither chat nor terminal can collapse to nothing).
+    pub pty_pct: u16,
+    /// Roster column width in cells. `0` hides the roster entirely.
+    pub roster_width: u16,
+    /// Fullscreen state (not all presets care; defaults to `Normal`).
+    pub zoom: Zoom,
+}
+
+impl Default for Layout {
+    fn default() -> Self {
+        Self {
+            pty_pct: 55,
+            roster_width: 22,
+            zoom: Zoom::Normal,
+        }
+    }
+}
+
+impl Layout {
+    /// Lower/upper bounds for the terminal's height share.
+    pub const MIN_PCT: u16 = 20;
+    pub const MAX_PCT: u16 = 90;
+    /// Upper bound on roster width (keeps it from eating the whole chat column).
+    pub const MAX_ROSTER: u16 = 60;
+
+    /// Re-clamp every field into its valid range. Call after any mutation that
+    /// came from user input so out-of-range values can never reach the layout.
+    pub fn clamp(&mut self) {
+        self.pty_pct = self.pty_pct.clamp(Self::MIN_PCT, Self::MAX_PCT);
+        self.roster_width = self.roster_width.min(Self::MAX_ROSTER);
+    }
+
+    /// The terminal's effective height share once zoom is taken into account:
+    /// `Term` fills the body (100%); `Normal`/`Chat` use the stored split (the
+    /// terminal is simply not painted under `Chat`, so its size stays steady).
+    pub fn effective_pty_pct(&self) -> u16 {
+        match self.zoom {
+            Zoom::Term => 100,
+            _ => self.pty_pct,
+        }
+    }
+
+    /// Cycle the fullscreen state: Normal → Term → Chat → Normal. Bound to F4.
+    pub fn cycle_zoom(&mut self) {
+        self.zoom = match self.zoom {
+            Zoom::Normal => Zoom::Term,
+            Zoom::Term => Zoom::Chat,
+            Zoom::Chat => Zoom::Normal,
+        };
+    }
+
+    /// Grow the terminal pane by `step` percent (drops out of any zoom first so
+    /// the change is visible). Stays within [MIN_PCT, MAX_PCT].
+    pub fn grow_pty(&mut self, step: u16) {
+        self.zoom = Zoom::Normal;
+        self.pty_pct = (self.pty_pct + step).min(Self::MAX_PCT);
+    }
+
+    /// Shrink the terminal pane by `step` percent (counterpart of `grow_pty`).
+    pub fn shrink_pty(&mut self, step: u16) {
+        self.zoom = Zoom::Normal;
+        self.pty_pct = self.pty_pct.saturating_sub(step).max(Self::MIN_PCT);
+    }
+
+    /// A one-line description of the current arrangement (for `/layout`).
+    pub fn describe(&self) -> String {
+        let zoom = match self.zoom {
+            Zoom::Normal => "split",
+            Zoom::Term => "terminal-fullscreen",
+            Zoom::Chat => "chat-fullscreen",
+        };
+        let roster = if self.roster_width == 0 {
+            "off".to_string()
+        } else {
+            self.roster_width.to_string()
+        };
+        format!(
+            "terminal {}% · chat {}% · roster {} · {}",
+            self.pty_pct,
+            100 - self.pty_pct,
+            roster,
+            zoom
+        )
+    }
+
+    /// Persist this arrangement to `layouts/<slug>.toml` so it can be re-applied
+    /// later with `/layout load <slug>`. Returns the slug actually written.
+    pub fn save(&self, name: &str) -> anyhow::Result<String> {
+        let slug = slugify(name);
+        anyhow::ensure!(!slug.is_empty(), "give the layout a name (letters/digits)");
+        std::fs::create_dir_all(LAYOUTS_DIR)
+            .with_context(|| format!("creating {LAYOUTS_DIR}"))?;
+        let path = format!("{LAYOUTS_DIR}/{slug}.toml");
+        let body = toml::to_string_pretty(self)
+            .with_context(|| format!("serialize layout '{slug}'"))?;
+        std::fs::write(&path, body).with_context(|| format!("write {path}"))?;
+        Ok(slug)
+    }
+
+    /// Load a saved arrangement by name (`layouts/<slug>.toml`), re-clamped.
+    pub fn by_name(name: &str) -> anyhow::Result<Self> {
+        let slug = slugify(name);
+        let path = format!("{LAYOUTS_DIR}/{slug}.toml");
+        let s = std::fs::read_to_string(&path)
+            .with_context(|| format!("layout '{slug}' ({path})"))?;
+        let mut l: Layout = toml::from_str(&s)?;
+        l.clamp();
+        Ok(l)
+    }
+
+    /// Names of saved presets, sorted, for `/layout list`.
+    pub fn available() -> Vec<String> {
+        let mut names: Vec<String> = std::fs::read_dir(LAYOUTS_DIR)
+            .into_iter()
+            .flatten()
+            .flatten()
+            .filter_map(|e| {
+                e.file_name()
+                    .to_str()
+                    .and_then(|f| f.strip_suffix(".toml"))
+                    .map(str::to_string)
+            })
+            .collect();
+        names.sort();
+        names
+    }
+
+    /// Delete a saved preset. Errors if it doesn't exist.
+    pub fn remove(name: &str) -> anyhow::Result<()> {
+        let slug = slugify(name);
+        let path = format!("{LAYOUTS_DIR}/{slug}.toml");
+        std::fs::remove_file(&path).with_context(|| format!("no saved layout '{slug}'"))?;
+        Ok(())
+    }
+}
+
+/// Reduce a free-form name to a safe lowercase `<slug>` (ascii letters/digits,
+/// any other run folded to a single '-'), matching theme.rs's convention.
+fn slugify(name: &str) -> String {
+    let mut out = String::new();
+    let mut dash = false;
+    for c in name.trim().chars() {
+        if c.is_ascii_alphanumeric() {
+            if dash && !out.is_empty() {
+                out.push('-');
+            }
+            out.extend(c.to_lowercase());
+            dash = false;
+        } else {
+            dash = true;
+        }
+    }
+    out
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn clamp_bounds_pct_and_roster() {
+        let mut l = Layout {
+            pty_pct: 999,
+            roster_width: 999,
+            zoom: Zoom::Normal,
+        };
+        l.clamp();
+        assert_eq!(l.pty_pct, Layout::MAX_PCT);
+        assert_eq!(l.roster_width, Layout::MAX_ROSTER);
+        let mut low = Layout {
+            pty_pct: 1,
+            roster_width: 0,
+            zoom: Zoom::Normal,
+        };
+        low.clamp();
+        assert_eq!(low.pty_pct, Layout::MIN_PCT);
+        assert_eq!(low.roster_width, 0); // 0 is valid (hidden)
+    }
+
+    #[test]
+    fn effective_pct_full_under_term_zoom() {
+        let mut l = Layout::default();
+        assert_eq!(l.effective_pty_pct(), 55);
+        l.zoom = Zoom::Term;
+        assert_eq!(l.effective_pty_pct(), 100);
+        l.zoom = Zoom::Chat;
+        assert_eq!(l.effective_pty_pct(), 55); // chat hidden ≠ resize the pty
+    }
+
+    #[test]
+    fn cycle_and_resize_drop_out_of_zoom() {
+        let mut l = Layout::default();
+        l.cycle_zoom();
+        assert_eq!(l.zoom, Zoom::Term);
+        l.grow_pty(5);
+        assert_eq!(l.zoom, Zoom::Normal);
+        assert_eq!(l.pty_pct, 60);
+        l.shrink_pty(100);
+        assert_eq!(l.pty_pct, Layout::MIN_PCT);
+    }
+}

hh/src/main.rs

@@ -7,6 +7,7 @@
 mod app;
 mod crypto;
 mod ft;
+mod layout;
 mod net;
 mod sbx;
 mod theme;

hh/src/ui.rs

@@ -1,9 +1,10 @@
 //! ratatui rendering — top bar, chat, roster, input.
 
 use crate::app::{App, ChatLine, Role};
+use crate::layout::Zoom;
 use crate::theme::Theme;
 use ratatui::layout::{Constraint, Layout, Position, Rect};
-use ratatui::style::{Modifier, Style};
+use ratatui::style::{Color, Modifier, Style};
 use ratatui::text::{Line, Span};
 use ratatui::widgets::{Block, Clear, List, ListItem, Paragraph, Wrap};
 use ratatui::Frame;
@@ -26,20 +27,17 @@ pub fn draw(f: &mut Frame, app: &App, theme: &Theme) {
 
     draw_top(f, rows[0], app, theme);
 
-    // When a sandbox is live, split the body: chat+roster on top, PTY below.
-    let (chat_area, sbx_area) = if app.sandbox.is_some() {
-        let split = Layout::vertical([Constraint::Percentage(45), Constraint::Percentage(55)])
-            .split(rows[1]);
-        (split[0], Some(split[1]))
-    } else {
-        (rows[1], None)
-    };
-
-    let body = Layout::horizontal([Constraint::Min(1), Constraint::Length(theme.roster_width)])
-        .split(chat_area);
-    draw_chat(f, body[0], app, theme);
-    draw_roster(f, body[1], app, theme);
-    if let Some(area) = sbx_area {
+    // Divide the body into chat / roster / sandbox-terminal rects. `body_areas`
+    // is the single source of truth for that geometry, shared with `pane_at`
+    // (mouse hit-testing) so what you click is exactly what's painted.
+    let areas = body_areas(rows[1], app);
+    if let Some(chat_area) = areas.chat {
+        draw_chat(f, chat_area, app, theme);
+    }
+    if let Some(roster_area) = areas.roster {
+        draw_roster(f, roster_area, app, theme);
+    }
+    if let Some(area) = areas.sbx {
         draw_sandbox(f, area, app, theme);
     }
     draw_input(f, rows[2], app, theme);
@@ -55,6 +53,101 @@ pub fn draw(f: &mut Frame, app: &App, theme: &Theme) {
     }
 }
 
+/// The body's pane rectangles. Any field is `None` when that pane is hidden
+/// (terminal absent, fullscreen zoom, or roster width 0).
+struct BodyAreas {
+    chat: Option<Rect>,
+    roster: Option<Rect>,
+    sbx: Option<Rect>,
+}
+
+/// Carve the body region (`rows[1]`) into chat / roster / sandbox rectangles,
+/// honouring the sandbox presence, `Zoom`, and roster width. This is the single
+/// source of truth used by both `draw` (painting) and `pane_at` (hit-testing).
+fn body_areas(body: Rect, app: &App) -> BodyAreas {
+    // Vertical split: chat-column vs sandbox terminal.
+    let (chat_col, sbx) = if app.sandbox.is_some() {
+        match app.layout.zoom {
+            Zoom::Term => (None, Some(body)), // terminal fullscreen
+            Zoom::Chat => (Some(body), None), // chat fullscreen (terminal hidden)
+            Zoom::Normal => {
+                let pty = app.layout.pty_pct;
+                let split = Layout::vertical([
+                    Constraint::Percentage(100 - pty),
+                    Constraint::Percentage(pty),
+                ])
+                .split(body);
+                (Some(split[0]), Some(split[1]))
+            }
+        }
+    } else {
+        (Some(body), None) // no sandbox → chat owns the whole body
+    };
+
+    // Horizontal split of the chat column into chat vs roster.
+    let (chat, roster) = match chat_col {
+        Some(col) if app.layout.roster_width != 0 => {
+            let lr = Layout::horizontal([
+                Constraint::Min(1),
+                Constraint::Length(app.layout.roster_width),
+            ])
+            .split(col);
+            (Some(lr[0]), Some(lr[1]))
+        }
+        Some(col) => (Some(col), None), // roster hidden
+        None => (None, None),
+    };
+
+    BodyAreas { chat, roster, sbx }
+}
+
+/// Hit-test a screen cell against the laid-out panes, for click-to-select in
+/// interactive layout editing. Recomputes the exact rects `draw` used (via the
+/// shared `body_areas`) so a click lands on the pane the user actually sees.
+pub fn pane_at(w: u16, h: u16, app: &App, col: u16, row: u16) -> Option<crate::app::Pane> {
+    use crate::app::Pane;
+    let area = Rect {
+        x: 0,
+        y: 0,
+        width: w,
+        height: h,
+    };
+    // Mirror draw()'s top-bar / body / input split; only the body is selectable.
+    let rows = Layout::vertical([
+        Constraint::Length(1),
+        Constraint::Min(1),
+        Constraint::Length(3),
+    ])
+    .split(area);
+    let areas = body_areas(rows[1], app);
+    let p = Position { x: col, y: row };
+    if areas.sbx.is_some_and(|r| r.contains(p)) {
+        Some(Pane::Terminal)
+    } else if areas.roster.is_some_and(|r| r.contains(p)) {
+        Some(Pane::Roster)
+    } else if areas.chat.is_some_and(|r| r.contains(p)) {
+        Some(Pane::Chat)
+    } else {
+        None
+    }
+}
+
+/// Border decoration for a pane: when it's the one selected for interactive
+/// resize (F5 / click), give it a bold accent border and an "✎" title marker so
+/// it's obvious which pane the arrows will move; otherwise the plain `base`.
+fn edit_decor(app: &App, pane: crate::app::Pane, theme: &Theme, base: Color) -> (Style, &'static str) {
+    if app.focused_pane == Some(pane) {
+        (
+            Style::default()
+                .fg(theme.accent)
+                .add_modifier(Modifier::BOLD),
+            "✎ ",
+        )
+    } else {
+        (Style::default().fg(base), "")
+    }
+}
+
 /// Transient error popup, anchored top-right over the clergy so it never bleeds
 /// onto the input box. Cleared by the next keypress (see the run loop).
 fn draw_error(f: &mut Frame, area: Rect, theme: &Theme, msg: &str) {
@@ -267,11 +360,34 @@ fn help_clusters(theme: &Theme) -> Vec<HelpCluster> {
                 ),
             ],
         },
+        HelpCluster {
+            title: "LAYOUT (resize panes)",
+            items: vec![
+                kv("F4", "fullscreen the terminal (cycle: terminal → chat → split)"),
+                kv(
+                    "click a pane  ·  F5",
+                    "select a pane to resize (✎ marks it) — F5 cycles terminal → chat → roster",
+                ),
+                kv(
+                    "↑ / ↓  (terminal/chat selected)",
+                    "grow / shrink that pane's height share",
+                ),
+                kv("← / →  (roster selected)", "narrow / widen the roster column"),
+                kv("Esc / Enter", "finish editing the selected pane"),
+                kv("/layout reset", "restore the default split"),
+                kv(
+                    "/layout save <name>  ·  load <name>",
+                    "remember an arrangement and re-apply it later",
+                ),
+                kv("/layout list  ·  rm <name>", "list or delete saved layouts"),
+            ],
+        },
         HelpCluster {
             title: "KEYS",
             items: vec![
                 kv("Enter", "send chat message"),
                 kv("F1  ·  /help", "toggle this help"),
+                kv("F4 · F5 · click", "layout: fullscreen terminal · select pane to resize (see LAYOUT)"),
                 kv("Ctrl-C  (while driving)", "interrupt the running command"),
                 kv(
                     "Ctrl-X  (owner, not driving)",
@@ -472,15 +588,16 @@ fn draw_sandbox(f: &mut Frame, area: ratatui::layout::Rect, app: &App, theme: &T
     } else {
         " · /drive (or F2) · ↑/↓/wheel scroll".to_string()
     };
-    let title = format!(" sandbox · {}{} ", sv.backend, drive);
-    let border = if app.driving {
+    let base = if app.driving {
         theme.accent
     } else {
         theme.border
     };
+    let (border_style, mark) = edit_decor(app, crate::app::Pane::Terminal, theme, base);
+    let title = format!(" {mark}sandbox · {}{} ", sv.backend, drive);
     let pane = Paragraph::new(lines).block(
         Block::bordered()
-            .border_style(Style::default().fg(border))
+            .border_style(border_style)
             .title(Span::styled(title, Style::default().fg(theme.title))),
     );
     f.render_widget(pane, area);
@@ -586,15 +703,16 @@ fn draw_chat(f: &mut Frame, area: ratatui::layout::Rect, app: &App, theme: &Them
     let max_scroll = total_rows.saturating_sub(inner_h);
     let scroll = max_scroll.saturating_sub(app.chat_scroll) as u16;
 
+    let (border_style, mark) = edit_decor(app, crate::app::Pane::Chat, theme, theme.border);
     let title = if app.chat_scroll > 0 {
-        format!(" chat ↑{} (End=live) ", app.chat_scroll)
+        format!(" {mark}chat ↑{} (End=live) ", app.chat_scroll)
     } else {
-        " chat ".to_string()
+        format!(" {mark}chat ")
     };
     let chat = Paragraph::new(lines)
         .block(
             Block::bordered()
-                .border_style(Style::default().fg(theme.border))
+                .border_style(border_style)
                 .title(Span::styled(title, Style::default().fg(theme.title))),
         )
         .wrap(Wrap { trim: false })
@@ -639,10 +757,14 @@ fn draw_roster(f: &mut Frame, area: ratatui::layout::Rect, app: &App, theme: &Th
             )))
         })
         .collect();
+    let (border_style, mark) = edit_decor(app, crate::app::Pane::Roster, theme, theme.border);
     let roster = List::new(items).block(
         Block::bordered()
-            .border_style(Style::default().fg(theme.border))
-            .title(Span::styled(" clergy ", Style::default().fg(theme.title))),
+            .border_style(border_style)
+            .title(Span::styled(
+                format!(" {mark}clergy "),
+                Style::default().fg(theme.title),
+            )),
     );
     f.render_widget(roster, area);
 }