diff --git a/Cargo.lock b/Cargo.lock
index 0dc420a..3ff1aea 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -17,6 +17,12 @@ version = "1.0.102"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "7f202df86484c868dbad7eaa557ef785d5c66295e41b460ef922eca0723b842c"
 
+[[package]]
+name = "arrayvec"
+version = "0.7.7"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f02882884d3e1bc524fb12c79f107f6ad0e1cfd498c536ffb494301740995dfe"
+
 [[package]]
 name = "beer"
 version = "0.0.0"
@@ -29,6 +35,8 @@ dependencies = [
  "smithay-client-toolkit",
  "tracing",
  "tracing-subscriber",
+ "unicode-width",
+ "vte",
  "wayland-client",
 ]
 
@@ -479,6 +487,12 @@ version = "1.0.24"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "e6e4313cd5fcd3dad5cafa179702e2b244f760991f45397d14d4ebf38247da75"
 
+[[package]]
+name = "unicode-width"
+version = "0.2.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "b4ac048d71ede7ee76d585517add45da530660ef4390e49b098733c6e897f254"
+
 [[package]]
 name = "valuable"
 version = "0.1.1"
@@ -495,6 +509,16 @@ dependencies = [
  "quote",
 ]
 
+[[package]]
+name = "vte"
+version = "0.15.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "a5924018406ce0063cd67f8e008104968b74b563ee1b85dde3ed1f7cb87d3dbd"
+dependencies = [
+ "arrayvec",
+ "memchr",
+]
+
 [[package]]
 name = "wayland-backend"
 version = "0.3.15"
diff --git a/Cargo.toml b/Cargo.toml
index 7f74023..122641a 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -16,6 +16,8 @@ rustix = { version = "1.1.4", features = ["pty", "process", "termios", "stdio",
 smithay-client-toolkit = "0.20.0"
 tracing = "0.1.44"
 tracing-subscriber = { version = "0.3.23", features = ["env-filter"] }
+unicode-width = "0.2.2"
+vte = "0.15.0"
 wayland-client = "0.31.14"
 
 [lints.rust]
diff --git a/src/grid.rs b/src/grid.rs
new file mode 100644
index 0000000..c7fecd6
--- /dev/null
+++ b/src/grid.rs
@@ -0,0 +1,632 @@
+//! The terminal screen: a grid of styled cells, a cursor, and the editing
+//! operations the VT parser drives.
+
+use unicode_width::UnicodeWidthChar;
+
+/// A cell colour: terminal default, a palette index, or direct RGB.
+#[derive(Clone, Copy, PartialEq, Eq, Debug, Default)]
+pub enum Color {
+    #[default]
+    Default,
+    Indexed(u8),
+    Rgb(u8, u8, u8),
+}
+
+/// Per-cell style flags, packed into a `u16`.
+#[derive(Clone, Copy, PartialEq, Eq, Debug, Default)]
+pub struct Flags(u16);
+
+impl Flags {
+    pub const BOLD: Self = Self(1 << 0);
+    pub const DIM: Self = Self(1 << 1);
+    pub const ITALIC: Self = Self(1 << 2);
+    pub const UNDERLINE: Self = Self(1 << 3);
+    pub const BLINK: Self = Self(1 << 4);
+    pub const REVERSE: Self = Self(1 << 5);
+    pub const HIDDEN: Self = Self(1 << 6);
+    pub const STRIKE: Self = Self(1 << 7);
+    /// Trailing column of a double-width glyph; holds no character of its own.
+    pub const WIDE_CONT: Self = Self(1 << 8);
+
+    pub const fn empty() -> Self {
+        Self(0)
+    }
+
+    pub const fn union(self, other: Self) -> Self {
+        Self(self.0 | other.0)
+    }
+
+    pub fn contains(self, other: Self) -> bool {
+        self.0 & other.0 == other.0
+    }
+
+    pub fn insert(&mut self, other: Self) {
+        self.0 |= other.0;
+    }
+
+    pub fn remove(&mut self, other: Self) {
+        self.0 &= !other.0;
+    }
+}
+
+/// One grid cell: a character plus its rendering style.
+#[derive(Clone, PartialEq, Eq, Debug)]
+pub struct Cell {
+    pub c: char,
+    pub fg: Color,
+    pub bg: Color,
+    pub flags: Flags,
+}
+
+impl Default for Cell {
+    fn default() -> Self {
+        Self {
+            c: ' ',
+            fg: Color::Default,
+            bg: Color::Default,
+            flags: Flags::empty(),
+        }
+    }
+}
+
+#[derive(Clone, Copy, Debug, Default)]
+struct Cursor {
+    x: usize,
+    y: usize,
+}
+
+/// The active screen plus cursor, scroll region, and current pen.
+#[derive(Debug)]
+pub struct Grid {
+    cols: usize,
+    rows: usize,
+    lines: Vec<Vec<Cell>>,
+    cursor: Cursor,
+    saved: Cursor,
+    /// Inclusive top/bottom rows of the scroll region.
+    top: usize,
+    bottom: usize,
+    /// Template cell carrying the current SGR colours/flags.
+    pen: Cell,
+    autowrap: bool,
+    origin: bool,
+    insert: bool,
+    /// Cursor parked past the last column, awaiting the next print to wrap.
+    wrap_pending: bool,
+    tabs: Vec<bool>,
+    /// Saved primary screen while the alternate screen is active.
+    alt_saved: Option<Vec<Vec<Cell>>>,
+}
+
+fn default_tabs(cols: usize) -> Vec<bool> {
+    (0..cols).map(|i| i % 8 == 0 && i != 0).collect()
+}
+
+impl Grid {
+    pub fn new(cols: usize, rows: usize) -> Self {
+        let cols = cols.max(1);
+        let rows = rows.max(1);
+        Self {
+            cols,
+            rows,
+            lines: vec![vec![Cell::default(); cols]; rows],
+            cursor: Cursor::default(),
+            saved: Cursor::default(),
+            top: 0,
+            bottom: rows - 1,
+            pen: Cell::default(),
+            autowrap: true,
+            origin: false,
+            insert: false,
+            wrap_pending: false,
+            tabs: default_tabs(cols),
+            alt_saved: None,
+        }
+    }
+
+    pub fn rows(&self) -> usize {
+        self.rows
+    }
+
+    pub fn cursor(&self) -> (usize, usize) {
+        (self.cursor.x, self.cursor.y)
+    }
+
+    // --- pen / attributes ---
+
+    pub fn pen_mut(&mut self) -> &mut Cell {
+        &mut self.pen
+    }
+
+    pub fn reset_pen(&mut self) {
+        self.pen = Cell::default();
+    }
+
+    pub fn set_autowrap(&mut self, on: bool) {
+        self.autowrap = on;
+    }
+
+    pub fn set_origin(&mut self, on: bool) {
+        self.origin = on;
+        self.move_to(0, 0);
+    }
+
+    pub fn set_insert(&mut self, on: bool) {
+        self.insert = on;
+    }
+
+    // --- printing ---
+
+    /// Place a printable character at the cursor, honouring width and autowrap.
+    pub fn print(&mut self, c: char) {
+        let width = c.width().unwrap_or(0);
+        if width == 0 {
+            // Combining/zero-width: no standalone storage yet.
+            return;
+        }
+        if self.wrap_pending {
+            self.cursor.x = 0;
+            self.line_feed();
+            self.wrap_pending = false;
+        }
+        if width == 2 && self.cursor.x + 1 >= self.cols {
+            // A double-width glyph cannot straddle the right edge: wrap first.
+            if self.autowrap {
+                self.cursor.x = 0;
+                self.line_feed();
+            } else {
+                return;
+            }
+        }
+        if self.insert {
+            self.shift_right(width);
+        }
+
+        let (x, y) = (self.cursor.x, self.cursor.y);
+        let mut cell = self.pen.clone();
+        cell.c = c;
+        cell.flags.remove(Flags::WIDE_CONT);
+        self.lines[y][x] = cell;
+        if width == 2 && x + 1 < self.cols {
+            let mut cont = self.pen.clone();
+            cont.c = ' ';
+            cont.flags.insert(Flags::WIDE_CONT);
+            self.lines[y][x + 1] = cont;
+        }
+
+        let advance = width;
+        if self.cursor.x + advance >= self.cols {
+            if self.autowrap {
+                self.cursor.x = self.cols - 1;
+                self.wrap_pending = true;
+            } else {
+                self.cursor.x = self.cols - 1;
+            }
+        } else {
+            self.cursor.x += advance;
+        }
+    }
+
+    fn shift_right(&mut self, n: usize) {
+        let (x, y) = (self.cursor.x, self.cursor.y);
+        let end = self.cols;
+        let blank = self.pen_blank();
+        let row = &mut self.lines[y];
+        for i in (x + n..end).rev() {
+            row[i] = row[i - n].clone();
+        }
+        for cell in &mut row[x..(x + n).min(end)] {
+            *cell = blank.clone();
+        }
+    }
+
+    fn pen_blank(&self) -> Cell {
+        Cell {
+            c: ' ',
+            fg: Color::Default,
+            bg: self.pen.bg,
+            flags: Flags::empty(),
+        }
+    }
+
+    // --- cursor movement ---
+
+    fn region(&self) -> (usize, usize) {
+        if self.origin {
+            (self.top, self.bottom)
+        } else {
+            (0, self.rows - 1)
+        }
+    }
+
+    pub fn move_to(&mut self, x: usize, y: usize) {
+        let (rt, rb) = self.region();
+        self.cursor.x = x.min(self.cols - 1);
+        self.cursor.y = (y + rt).min(rb).max(rt);
+        self.wrap_pending = false;
+    }
+
+    pub fn move_to_col(&mut self, x: usize) {
+        self.cursor.x = x.min(self.cols - 1);
+        self.wrap_pending = false;
+    }
+
+    pub fn move_to_row(&mut self, y: usize) {
+        let (rt, rb) = self.region();
+        self.cursor.y = (y + rt).min(rb).max(rt);
+        self.wrap_pending = false;
+    }
+
+    pub fn cursor_up(&mut self, n: usize) {
+        let (rt, _) = self.region();
+        self.cursor.y = self.cursor.y.saturating_sub(n).max(rt);
+        self.wrap_pending = false;
+    }
+
+    pub fn cursor_down(&mut self, n: usize) {
+        let (_, rb) = self.region();
+        self.cursor.y = (self.cursor.y + n).min(rb);
+        self.wrap_pending = false;
+    }
+
+    pub fn cursor_fwd(&mut self, n: usize) {
+        self.cursor.x = (self.cursor.x + n).min(self.cols - 1);
+        self.wrap_pending = false;
+    }
+
+    pub fn cursor_back(&mut self, n: usize) {
+        self.cursor.x = self.cursor.x.saturating_sub(n);
+        self.wrap_pending = false;
+    }
+
+    pub fn save_cursor(&mut self) {
+        self.saved = self.cursor;
+    }
+
+    pub fn restore_cursor(&mut self) {
+        self.cursor = self.saved;
+        self.cursor.x = self.cursor.x.min(self.cols - 1);
+        self.cursor.y = self.cursor.y.min(self.rows - 1);
+        self.wrap_pending = false;
+    }
+
+    // --- line discipline ---
+
+    pub fn carriage_return(&mut self) {
+        self.cursor.x = 0;
+        self.wrap_pending = false;
+    }
+
+    pub fn backspace(&mut self) {
+        self.cursor.x = self.cursor.x.saturating_sub(1);
+        self.wrap_pending = false;
+    }
+
+    /// LF/VT/FF: move down one row, scrolling at the region bottom.
+    pub fn line_feed(&mut self) {
+        if self.cursor.y == self.bottom {
+            self.scroll_up(1);
+        } else if self.cursor.y < self.rows - 1 {
+            self.cursor.y += 1;
+        }
+        self.wrap_pending = false;
+    }
+
+    /// RI: move up one row, scrolling down at the region top.
+    pub fn reverse_index(&mut self) {
+        if self.cursor.y == self.top {
+            self.scroll_down(1);
+        } else if self.cursor.y > 0 {
+            self.cursor.y -= 1;
+        }
+        self.wrap_pending = false;
+    }
+
+    /// NEL: carriage return plus line feed.
+    pub fn next_line(&mut self) {
+        self.carriage_return();
+        self.line_feed();
+    }
+
+    // --- tab stops ---
+
+    pub fn tab(&mut self) {
+        let mut x = self.cursor.x + 1;
+        while x < self.cols && !self.tabs[x] {
+            x += 1;
+        }
+        self.cursor.x = x.min(self.cols - 1);
+        self.wrap_pending = false;
+    }
+
+    pub fn set_tab(&mut self) {
+        if self.cursor.x < self.cols {
+            self.tabs[self.cursor.x] = true;
+        }
+    }
+
+    pub fn clear_tab(&mut self) {
+        if self.cursor.x < self.cols {
+            self.tabs[self.cursor.x] = false;
+        }
+    }
+
+    pub fn clear_all_tabs(&mut self) {
+        self.tabs.iter_mut().for_each(|t| *t = false);
+    }
+
+    // --- scrolling within the region ---
+
+    pub fn set_scroll_region(&mut self, top: usize, bottom: usize) {
+        if top < bottom && bottom < self.rows {
+            self.top = top;
+            self.bottom = bottom;
+        } else {
+            self.top = 0;
+            self.bottom = self.rows - 1;
+        }
+        self.move_to(0, 0);
+    }
+
+    pub fn scroll_up(&mut self, n: usize) {
+        let n = n.min(self.bottom - self.top + 1);
+        for y in self.top..=self.bottom {
+            if y + n <= self.bottom {
+                self.lines.swap(y, y + n);
+            }
+        }
+        for y in (self.bottom + 1 - n)..=self.bottom {
+            self.blank_row(y);
+        }
+    }
+
+    pub fn scroll_down(&mut self, n: usize) {
+        let n = n.min(self.bottom - self.top + 1);
+        for y in (self.top..=self.bottom).rev() {
+            if y >= self.top + n {
+                self.lines.swap(y, y - n);
+            }
+        }
+        for y in self.top..(self.top + n) {
+            self.blank_row(y);
+        }
+    }
+
+    fn blank_row(&mut self, y: usize) {
+        let blank = self.pen_blank();
+        for cell in &mut self.lines[y] {
+            *cell = blank.clone();
+        }
+    }
+
+    // --- erase ---
+
+    /// ED: 0=below, 1=above, 2/3=all.
+    pub fn erase_display(&mut self, mode: u16) {
+        let (x, y) = (self.cursor.x, self.cursor.y);
+        match mode {
+            0 => {
+                self.erase_in_row(y, x, self.cols);
+                for r in (y + 1)..self.rows {
+                    self.blank_row(r);
+                }
+            }
+            1 => {
+                for r in 0..y {
+                    self.blank_row(r);
+                }
+                self.erase_in_row(y, 0, x + 1);
+            }
+            _ => {
+                for r in 0..self.rows {
+                    self.blank_row(r);
+                }
+            }
+        }
+        self.wrap_pending = false;
+    }
+
+    /// EL: 0=right, 1=left, 2=line.
+    pub fn erase_line(&mut self, mode: u16) {
+        let (x, y) = (self.cursor.x, self.cursor.y);
+        match mode {
+            0 => self.erase_in_row(y, x, self.cols),
+            1 => self.erase_in_row(y, 0, x + 1),
+            _ => self.erase_in_row(y, 0, self.cols),
+        }
+        self.wrap_pending = false;
+    }
+
+    /// ECH: erase n characters from the cursor without moving it.
+    pub fn erase_chars(&mut self, n: usize) {
+        let (x, y) = (self.cursor.x, self.cursor.y);
+        self.erase_in_row(y, x, (x + n).min(self.cols));
+    }
+
+    fn erase_in_row(&mut self, y: usize, from: usize, to: usize) {
+        let blank = self.pen_blank();
+        for cell in &mut self.lines[y][from..to.min(self.cols)] {
+            *cell = blank.clone();
+        }
+    }
+
+    // --- intra-line editing ---
+
+    /// ICH: insert n blanks at the cursor, shifting the rest right.
+    pub fn insert_chars(&mut self, n: usize) {
+        let saved = self.insert;
+        self.insert = true;
+        self.shift_right(n.min(self.cols));
+        self.insert = saved;
+    }
+
+    /// DCH: delete n characters at the cursor, shifting the rest left.
+    pub fn delete_chars(&mut self, n: usize) {
+        let (x, y) = (self.cursor.x, self.cursor.y);
+        let n = n.min(self.cols - x);
+        let blank = self.pen_blank();
+        let row = &mut self.lines[y];
+        for i in x..self.cols {
+            row[i] = if i + n < self.cols {
+                row[i + n].clone()
+            } else {
+                blank.clone()
+            };
+        }
+    }
+
+    /// IL: insert n blank lines at the cursor row, within the scroll region.
+    pub fn insert_lines(&mut self, n: usize) {
+        if self.cursor.y < self.top || self.cursor.y > self.bottom {
+            return;
+        }
+        let n = n.min(self.bottom - self.cursor.y + 1);
+        for y in (self.cursor.y..=self.bottom).rev() {
+            if y >= self.cursor.y + n {
+                self.lines.swap(y, y - n);
+            }
+        }
+        for y in self.cursor.y..(self.cursor.y + n) {
+            self.blank_row(y);
+        }
+    }
+
+    /// DL: delete n lines at the cursor row, within the scroll region.
+    pub fn delete_lines(&mut self, n: usize) {
+        if self.cursor.y < self.top || self.cursor.y > self.bottom {
+            return;
+        }
+        let n = n.min(self.bottom - self.cursor.y + 1);
+        for y in self.cursor.y..=self.bottom {
+            if y + n <= self.bottom {
+                self.lines.swap(y, y + n);
+            }
+        }
+        for y in (self.bottom + 1 - n)..=self.bottom {
+            self.blank_row(y);
+        }
+    }
+
+    // --- alternate screen ---
+
+    pub fn enter_alt_screen(&mut self) {
+        if self.alt_saved.is_some() {
+            return;
+        }
+        let blank = vec![vec![Cell::default(); self.cols]; self.rows];
+        self.alt_saved = Some(std::mem::replace(&mut self.lines, blank));
+    }
+
+    pub fn leave_alt_screen(&mut self) {
+        if let Some(main) = self.alt_saved.take() {
+            self.lines = main;
+        }
+    }
+
+    // --- inspection (logging + tests) ---
+
+    /// The visible text of one row, trailing blanks trimmed.
+    pub fn row_text(&self, y: usize) -> String {
+        self.lines[y]
+            .iter()
+            .filter(|c| !c.flags.contains(Flags::WIDE_CONT))
+            .map(|c| c.c)
+            .collect::<String>()
+            .trim_end()
+            .to_string()
+    }
+
+    #[cfg(test)]
+    pub fn cell(&self, x: usize, y: usize) -> &Cell {
+        &self.lines[y][x]
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn prints_and_wraps() {
+        let mut g = Grid::new(4, 2);
+        for c in "abcde".chars() {
+            g.print(c);
+        }
+        assert_eq!(g.row_text(0), "abcd");
+        assert_eq!(g.row_text(1), "e");
+        assert_eq!(g.cursor(), (1, 1));
+    }
+
+    #[test]
+    fn carriage_return_and_line_feed() {
+        let mut g = Grid::new(8, 4);
+        for c in "hi".chars() {
+            g.print(c);
+        }
+        g.carriage_return();
+        g.line_feed();
+        for c in "yo".chars() {
+            g.print(c);
+        }
+        assert_eq!(g.row_text(0), "hi");
+        assert_eq!(g.row_text(1), "yo");
+    }
+
+    #[test]
+    fn line_feed_scrolls_at_bottom() {
+        let mut g = Grid::new(4, 2);
+        g.print('a');
+        g.next_line();
+        g.print('b');
+        g.next_line(); // scrolls: row0 <- "b", row1 blank
+        assert_eq!(g.row_text(0), "b");
+        assert_eq!(g.row_text(1), "");
+    }
+
+    #[test]
+    fn erase_line_to_right() {
+        let mut g = Grid::new(6, 1);
+        for c in "abcdef".chars() {
+            g.print(c);
+        }
+        g.move_to(2, 0);
+        g.erase_line(0);
+        assert_eq!(g.row_text(0), "ab");
+    }
+
+    #[test]
+    fn delete_and_insert_chars() {
+        let mut g = Grid::new(6, 1);
+        for c in "abcdef".chars() {
+            g.print(c);
+        }
+        g.move_to(1, 0);
+        g.delete_chars(2);
+        assert_eq!(g.row_text(0), "adef");
+        g.move_to(1, 0);
+        g.insert_chars(2);
+        assert_eq!(g.row_text(0), "a  def");
+    }
+
+    #[test]
+    fn wide_char_occupies_two_columns() {
+        let mut g = Grid::new(6, 1);
+        g.print('世');
+        g.print('x');
+        assert_eq!(g.cell(0, 0).c, '世');
+        assert!(g.cell(1, 0).flags.contains(Flags::WIDE_CONT));
+        assert_eq!(g.cell(2, 0).c, 'x');
+    }
+
+    #[test]
+    fn scroll_region_limits_line_feed() {
+        let mut g = Grid::new(4, 4);
+        g.set_scroll_region(1, 2);
+        g.move_to(0, 2); // bottom of region (origin off: absolute row 2)
+        g.print('x');
+        g.move_to(0, 2);
+        g.line_feed(); // at region bottom: scroll [1,2] up, x moves to row 1
+        assert_eq!(g.row_text(1), "x");
+        assert_eq!(g.row_text(2), "");
+    }
+}
diff --git a/src/main.rs b/src/main.rs
index 7634bed..80d2128 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -1,6 +1,8 @@
 //! beer, a fast, software-rendered, Wayland-native terminal emulator.
 
+mod grid;
 mod pty;
+mod vt;
 mod wayland;
 
 use std::process::ExitCode;
diff --git a/src/vt.rs b/src/vt.rs
new file mode 100644
index 0000000..ab6bc9f
--- /dev/null
+++ b/src/vt.rs
@@ -0,0 +1,459 @@
+//! VT emulation: feed bytes through `vte` and drive the [`Grid`].
+
+use std::io::Write as _;
+
+use vte::{Params, Perform};
+
+use crate::grid::{Color, Flags, Grid};
+
+/// G0/G1 character set designation.
+#[derive(Clone, Copy, PartialEq, Eq, Debug)]
+enum Charset {
+    Ascii,
+    DecSpecial,
+}
+
+/// The terminal model: a grid plus the escape-sequence state around it.
+#[derive(Debug)]
+pub struct Term {
+    grid: Grid,
+    title: Option<String>,
+    response: Vec<u8>,
+    g0: Charset,
+    g1: Charset,
+    shift_out: bool,
+}
+
+impl Term {
+    pub fn new(cols: usize, rows: usize) -> Self {
+        Self {
+            grid: Grid::new(cols, rows),
+            title: None,
+            response: Vec::new(),
+            g0: Charset::Ascii,
+            g1: Charset::Ascii,
+            shift_out: false,
+        }
+    }
+
+    pub fn grid(&self) -> &Grid {
+        &self.grid
+    }
+
+    pub fn title(&self) -> Option<&str> {
+        self.title.as_deref()
+    }
+
+    /// Bytes the terminal needs to send back to the application (DA, CPR, ...).
+    pub fn take_response(&mut self) -> Vec<u8> {
+        std::mem::take(&mut self.response)
+    }
+
+    fn active_charset(&self) -> Charset {
+        if self.shift_out { self.g1 } else { self.g0 }
+    }
+
+    fn set_mode(&mut self, params: &Params, private: bool, on: bool) {
+        for p in params.iter() {
+            let Some(&code) = p.first() else { continue };
+            match (private, code) {
+                (true, 6) => self.grid.set_origin(on),
+                (true, 7) => self.grid.set_autowrap(on),
+                (true, 1049) => {
+                    if on {
+                        self.grid.save_cursor();
+                        self.grid.enter_alt_screen();
+                        self.grid.erase_display(2);
+                    } else {
+                        self.grid.leave_alt_screen();
+                        self.grid.restore_cursor();
+                    }
+                }
+                (true, 47 | 1047) => {
+                    if on {
+                        self.grid.enter_alt_screen();
+                    } else {
+                        self.grid.leave_alt_screen();
+                    }
+                }
+                (false, 4) => self.grid.set_insert(on),
+                // App-cursor/bracketed-paste/mouse/sync modes affect input and
+                // rendering, which arrive with the keyboard and renderer.
+                _ => tracing::trace!("unhandled mode {code} private={private} on={on}"),
+            }
+        }
+    }
+
+    fn sgr(&mut self, params: &Params) {
+        let items: Vec<&[u16]> = params.iter().collect();
+        if items.is_empty() {
+            self.grid.reset_pen();
+            return;
+        }
+        let mut i = 0;
+        while i < items.len() {
+            let p = items[i];
+            let code = p.first().copied().unwrap_or(0);
+            let pen = self.grid.pen_mut();
+            let mut step = 1;
+            match code {
+                0 => *pen = Default::default(),
+                1 => pen.flags.insert(Flags::BOLD),
+                2 => pen.flags.insert(Flags::DIM),
+                3 => pen.flags.insert(Flags::ITALIC),
+                4 => pen.flags.insert(Flags::UNDERLINE),
+                5 | 6 => pen.flags.insert(Flags::BLINK),
+                7 => pen.flags.insert(Flags::REVERSE),
+                8 => pen.flags.insert(Flags::HIDDEN),
+                9 => pen.flags.insert(Flags::STRIKE),
+                21 | 22 => pen.flags.remove(Flags::BOLD.union(Flags::DIM)),
+                23 => pen.flags.remove(Flags::ITALIC),
+                24 => pen.flags.remove(Flags::UNDERLINE),
+                25 => pen.flags.remove(Flags::BLINK),
+                27 => pen.flags.remove(Flags::REVERSE),
+                28 => pen.flags.remove(Flags::HIDDEN),
+                29 => pen.flags.remove(Flags::STRIKE),
+                30..=37 => pen.fg = Color::Indexed((code - 30) as u8),
+                39 => pen.fg = Color::Default,
+                40..=47 => pen.bg = Color::Indexed((code - 40) as u8),
+                49 => pen.bg = Color::Default,
+                90..=97 => pen.fg = Color::Indexed((code - 90 + 8) as u8),
+                100..=107 => pen.bg = Color::Indexed((code - 100 + 8) as u8),
+                38 | 48 => {
+                    let (color, consumed) = ext_color(&items, i);
+                    if let Some(color) = color {
+                        if code == 38 {
+                            pen.fg = color;
+                        } else {
+                            pen.bg = color;
+                        }
+                    }
+                    step = consumed;
+                }
+                // 58/59 (underline colour) and others: no storage yet.
+                _ => {}
+            }
+            i += step;
+        }
+    }
+
+    fn device_attrs(&mut self, secondary: bool) {
+        // Claim a VT220 with ANSI colour (62;22) for DA1, and a generic
+        // firmware level for DA2.
+        if secondary {
+            self.response.extend_from_slice(b"\x1b[>0;276;0c");
+        } else {
+            self.response.extend_from_slice(b"\x1b[?62;22c");
+        }
+    }
+
+    fn device_status(&mut self, params: &Params) {
+        match params.iter().next().and_then(|p| p.first().copied()) {
+            Some(5) => self.response.extend_from_slice(b"\x1b[0n"),
+            Some(6) => {
+                let (x, y) = self.grid.cursor();
+                let _ = write!(self.response, "\x1b[{};{}R", y + 1, x + 1);
+            }
+            _ => {}
+        }
+    }
+}
+
+/// First param value, with 0/absent folded to `default` (xterm convention for
+/// cursor movement and counts).
+fn n(params: &Params, idx: usize, default: usize) -> usize {
+    match params.iter().nth(idx).and_then(|p| p.first().copied()) {
+        Some(0) | None => default,
+        Some(v) => v as usize,
+    }
+}
+
+/// Raw first param value (0 is meaningful), defaulting to 0 when absent.
+fn raw(params: &Params, idx: usize) -> u16 {
+    params
+        .iter()
+        .nth(idx)
+        .and_then(|p| p.first().copied())
+        .unwrap_or(0)
+}
+
+/// Parse an SGR 38/48 extended colour, returning the colour and how many
+/// top-level params it consumed (1 for colon form, more for semicolon form).
+fn ext_color(items: &[&[u16]], i: usize) -> (Option<Color>, usize) {
+    let head = items[i];
+    if head.len() >= 2 {
+        return (color_from_subparams(&head[1..]), 1);
+    }
+    match items.get(i + 1).and_then(|s| s.first().copied()) {
+        Some(5) => {
+            let idx = items
+                .get(i + 2)
+                .and_then(|s| s.first().copied())
+                .unwrap_or(0);
+            (Some(Color::Indexed(idx as u8)), 3)
+        }
+        Some(2) => {
+            let get = |k: usize| {
+                items
+                    .get(i + k)
+                    .and_then(|s| s.first().copied())
+                    .unwrap_or(0)
+            };
+            (
+                Some(Color::Rgb(get(2) as u8, get(3) as u8, get(4) as u8)),
+                5,
+            )
+        }
+        _ => (None, 1),
+    }
+}
+
+fn color_from_subparams(sub: &[u16]) -> Option<Color> {
+    match sub.first().copied() {
+        Some(5) => sub.get(1).map(|&i| Color::Indexed(i as u8)),
+        Some(2) => {
+            // Either `2:r:g:b` or `2:colorspace:r:g:b`.
+            let rgb = if sub.len() >= 5 {
+                &sub[2..5]
+            } else {
+                &sub[1..]
+            };
+            match rgb {
+                [r, g, b, ..] => Some(Color::Rgb(*r as u8, *g as u8, *b as u8)),
+                _ => None,
+            }
+        }
+        _ => None,
+    }
+}
+
+fn charset(byte: u8) -> Charset {
+    match byte {
+        b'0' => Charset::DecSpecial,
+        _ => Charset::Ascii,
+    }
+}
+
+/// Translate a byte under the DEC special graphics set (line drawing).
+fn dec_special(c: char) -> char {
+    match c {
+        '`' => '◆',
+        'a' => '▒',
+        'f' => '°',
+        'g' => '±',
+        'j' => '┘',
+        'k' => '┐',
+        'l' => '┌',
+        'm' => '└',
+        'n' => '┼',
+        'o' => '⎺',
+        'p' => '⎻',
+        'q' => '─',
+        'r' => '⎼',
+        's' => '⎽',
+        't' => '├',
+        'u' => '┤',
+        'v' => '┴',
+        'w' => '┬',
+        'x' => '│',
+        'y' => '≤',
+        'z' => '≥',
+        '~' => '·',
+        _ => c,
+    }
+}
+
+impl Perform for Term {
+    fn print(&mut self, c: char) {
+        let c = if self.active_charset() == Charset::DecSpecial {
+            dec_special(c)
+        } else {
+            c
+        };
+        self.grid.print(c);
+    }
+
+    fn execute(&mut self, byte: u8) {
+        match byte {
+            0x08 => self.grid.backspace(),
+            0x09 => self.grid.tab(),
+            0x0A..=0x0C => self.grid.line_feed(),
+            0x0D => self.grid.carriage_return(),
+            0x0E => self.shift_out = true,
+            0x0F => self.shift_out = false,
+            _ => {}
+        }
+    }
+
+    fn csi_dispatch(&mut self, params: &Params, intermediates: &[u8], _ignore: bool, action: char) {
+        let private = intermediates.first() == Some(&b'?');
+        let secondary = intermediates.first() == Some(&b'>');
+        match action {
+            'A' => self.grid.cursor_up(n(params, 0, 1)),
+            'B' | 'e' => self.grid.cursor_down(n(params, 0, 1)),
+            'C' | 'a' => self.grid.cursor_fwd(n(params, 0, 1)),
+            'D' => self.grid.cursor_back(n(params, 0, 1)),
+            'E' => {
+                self.grid.cursor_down(n(params, 0, 1));
+                self.grid.carriage_return();
+            }
+            'F' => {
+                self.grid.cursor_up(n(params, 0, 1));
+                self.grid.carriage_return();
+            }
+            'G' | '`' => self.grid.move_to_col(n(params, 0, 1) - 1),
+            'd' => self.grid.move_to_row(n(params, 0, 1) - 1),
+            'H' | 'f' => self.grid.move_to(n(params, 1, 1) - 1, n(params, 0, 1) - 1),
+            'J' => self.grid.erase_display(raw(params, 0)),
+            'K' => self.grid.erase_line(raw(params, 0)),
+            '@' => self.grid.insert_chars(n(params, 0, 1)),
+            'P' => self.grid.delete_chars(n(params, 0, 1)),
+            'L' => self.grid.insert_lines(n(params, 0, 1)),
+            'M' => self.grid.delete_lines(n(params, 0, 1)),
+            'X' => self.grid.erase_chars(n(params, 0, 1)),
+            'S' => self.grid.scroll_up(n(params, 0, 1)),
+            'T' => self.grid.scroll_down(n(params, 0, 1)),
+            'm' => self.sgr(params),
+            'r' => {
+                let top = n(params, 0, 1) - 1;
+                let bottom = match params.iter().nth(1).and_then(|p| p.first().copied()) {
+                    Some(0) | None => self.grid.rows() - 1,
+                    Some(v) => (v as usize).saturating_sub(1),
+                };
+                self.grid.set_scroll_region(top, bottom);
+            }
+            'h' => self.set_mode(params, private, true),
+            'l' => self.set_mode(params, private, false),
+            'c' => self.device_attrs(secondary),
+            'n' => self.device_status(params),
+            's' => self.grid.save_cursor(),
+            'u' => self.grid.restore_cursor(),
+            'g' => match raw(params, 0) {
+                3 => self.grid.clear_all_tabs(),
+                _ => self.grid.clear_tab(),
+            },
+            _ => tracing::trace!("unhandled CSI {action:?} {intermediates:?}"),
+        }
+    }
+
+    fn esc_dispatch(&mut self, intermediates: &[u8], _ignore: bool, byte: u8) {
+        match (intermediates.first().copied(), byte) {
+            (None, b'D') => self.grid.line_feed(),
+            (None, b'M') => self.grid.reverse_index(),
+            (None, b'E') => self.grid.next_line(),
+            (None, b'7') => self.grid.save_cursor(),
+            (None, b'8') => self.grid.restore_cursor(),
+            (None, b'H') => self.grid.set_tab(),
+            (None, b'c') => {
+                self.grid.reset_pen();
+                self.grid.set_scroll_region(0, self.grid.rows() - 1);
+                self.grid.set_autowrap(true);
+                self.grid.set_origin(false);
+                self.grid.erase_display(2);
+                self.grid.move_to(0, 0);
+                self.g0 = Charset::Ascii;
+                self.g1 = Charset::Ascii;
+                self.shift_out = false;
+            }
+            (Some(b'('), c) => self.g0 = charset(c),
+            (Some(b')'), c) => self.g1 = charset(c),
+            _ => {}
+        }
+    }
+
+    fn osc_dispatch(&mut self, params: &[&[u8]], _bell_terminated: bool) {
+        match params.first() {
+            Some(&n) if n == b"0" || n == b"2" => {
+                if let Some(text) = params.get(1) {
+                    self.title = Some(String::from_utf8_lossy(text).into_owned());
+                }
+            }
+            _ => {}
+        }
+    }
+
+    fn hook(&mut self, _: &Params, _: &[u8], _: bool, _: char) {}
+    fn put(&mut self, _: u8) {}
+    fn unhook(&mut self) {}
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    fn feed(term: &mut Term, bytes: &[u8]) {
+        let mut parser = vte::Parser::new();
+        parser.advance(term, bytes);
+    }
+
+    #[test]
+    fn plain_text_lands_in_the_grid() {
+        let mut t = Term::new(20, 4);
+        feed(&mut t, b"hello");
+        assert_eq!(t.grid().row_text(0), "hello");
+    }
+
+    #[test]
+    fn cursor_position_and_erase() {
+        let mut t = Term::new(20, 4);
+        feed(&mut t, b"abcde\x1b[Hxyz");
+        assert_eq!(t.grid().row_text(0), "xyzde");
+    }
+
+    #[test]
+    fn newline_sequence() {
+        let mut t = Term::new(20, 4);
+        feed(&mut t, b"one\r\ntwo");
+        assert_eq!(t.grid().row_text(0), "one");
+        assert_eq!(t.grid().row_text(1), "two");
+    }
+
+    #[test]
+    fn sgr_sets_pen_colours() {
+        let mut t = Term::new(20, 1);
+        feed(&mut t, b"\x1b[31;1mX");
+        let cell = t.grid().cell(0, 0);
+        assert_eq!(cell.fg, Color::Indexed(1));
+        assert!(cell.flags.contains(Flags::BOLD));
+    }
+
+    #[test]
+    fn truecolor_semicolon_and_colon() {
+        let mut t = Term::new(20, 1);
+        feed(&mut t, b"\x1b[38;2;10;20;30mA");
+        assert_eq!(t.grid().cell(0, 0).fg, Color::Rgb(10, 20, 30));
+        feed(&mut t, b"\x1b[38:2:40:50:60mB");
+        assert_eq!(t.grid().cell(1, 0).fg, Color::Rgb(40, 50, 60));
+    }
+
+    #[test]
+    fn device_status_reports_cursor() {
+        let mut t = Term::new(20, 4);
+        feed(&mut t, b"\x1b[3;5H\x1b[6n");
+        assert_eq!(t.take_response(), b"\x1b[3;5R");
+    }
+
+    #[test]
+    fn line_drawing_charset() {
+        let mut t = Term::new(20, 1);
+        feed(&mut t, b"\x1b(0qx\x1b(B");
+        assert_eq!(t.grid().row_text(0), "─│");
+    }
+
+    #[test]
+    fn title_via_osc() {
+        let mut t = Term::new(20, 1);
+        feed(&mut t, b"\x1b]0;hello\x07");
+        assert_eq!(t.title(), Some("hello"));
+    }
+
+    #[test]
+    fn alt_screen_preserves_primary() {
+        let mut t = Term::new(20, 2);
+        feed(&mut t, b"main");
+        feed(&mut t, b"\x1b[?1049h");
+        assert_eq!(t.grid().row_text(0), "");
+        feed(&mut t, b"\x1b[?1049l");
+        assert_eq!(t.grid().row_text(0), "main");
+    }
+}
diff --git a/src/wayland.rs b/src/wayland.rs
index cd4ad5e..7bae825 100644
--- a/src/wayland.rs
+++ b/src/wayland.rs
@@ -3,6 +3,7 @@
 //! Uses smithay-client-toolkit for protocol boilerplate and calloop for the
 //! event loop, so the PTY master fd and timers share one loop.
 
+use std::os::fd::OwnedFd;
 use std::time::Duration;
 
 use anyhow::Context;
@@ -11,6 +12,7 @@ use calloop::{EventLoop, Interest, Mode, PostAction};
 use calloop_wayland_source::WaylandSource;
 
 use crate::pty::Pty;
+use crate::vt::Term;
 use smithay_client_toolkit::{
     compositor::{CompositorHandler, CompositorState},
     delegate_compositor, delegate_output, delegate_registry, delegate_seat, delegate_shm,
@@ -39,7 +41,7 @@ const DEFAULT_W: u32 = 800;
 const DEFAULT_H: u32 = 600;
 /// Background fill, 0xAARRGGBB. Foot-ish dark grey.
 const BG: u32 = 0xFF18_1818;
-/// Terminal size handed to the shell until cell geometry drives it.
+/// Terminal size handed to the shell.
 const COLS: u16 = 80;
 const ROWS: u16 = 24;
 
@@ -72,15 +74,17 @@ pub fn run() -> anyhow::Result<()> {
         .context("create shm slot pool")?;
 
     let pty = Pty::spawn(COLS, ROWS).context("spawn shell on pty")?;
+    let term = Term::new(COLS as usize, ROWS as usize);
+    let mut parser = vte::Parser::new();
 
     // Read child output off a clone of the master; the original stays in `pty`
-    // for writes and resizing.
+    // for writing input back.
     let read_fd = pty.master().try_clone().context("clone pty master")?;
     event_loop
         .handle()
         .insert_source(
             Generic::new(read_fd, Interest::READ, Mode::Level),
-            |_, fd, app: &mut App| {
+            move |_, fd, app: &mut App| {
                 let mut buf = [0u8; 4096];
                 match rustix::io::read(&*fd, &mut buf) {
                     Ok(0) => {
@@ -88,7 +92,8 @@ pub fn run() -> anyhow::Result<()> {
                         Ok(PostAction::Remove)
                     }
                     Ok(n) => {
-                        tracing::debug!("pty -> {n} bytes: {:02x?}", &buf[..n]);
+                        parser.advance(&mut app.term, &buf[..n]);
+                        app.after_feed();
                         Ok(PostAction::Continue)
                     }
                     Err(rustix::io::Errno::INTR | rustix::io::Errno::AGAIN) => {
@@ -111,6 +116,8 @@ pub fn run() -> anyhow::Result<()> {
         pool,
         window,
         pty,
+        term,
+        title: None,
         width: DEFAULT_W,
         height: DEFAULT_H,
         configured: false,
@@ -125,6 +132,19 @@ pub fn run() -> anyhow::Result<()> {
     Ok(())
 }
 
+/// Write every byte to `fd`, retrying short writes and interrupts.
+fn write_all(fd: &OwnedFd, mut buf: &[u8]) -> rustix::io::Result<()> {
+    while !buf.is_empty() {
+        match rustix::io::write(fd, buf) {
+            Ok(0) => return Err(rustix::io::Errno::IO),
+            Ok(n) => buf = &buf[n..],
+            Err(rustix::io::Errno::INTR) => {}
+            Err(e) => return Err(e),
+        }
+    }
+    Ok(())
+}
+
 /// Window + Wayland client state shared across all protocol handlers.
 #[derive(Debug)]
 struct App {
@@ -135,6 +155,9 @@ struct App {
     pool: SlotPool,
     window: Window,
     pty: Pty,
+    term: Term,
+    /// Last title applied to the toplevel, to avoid redundant requests.
+    title: Option<String>,
     width: u32,
     height: u32,
     configured: bool,
@@ -142,6 +165,29 @@ struct App {
 }
 
 impl App {
+    /// After parsing child output: send any replies and sync the title.
+    fn after_feed(&mut self) {
+        let reply = self.term.take_response();
+        if !reply.is_empty()
+            && let Err(err) = write_all(self.pty.master(), &reply)
+        {
+            tracing::warn!("write to pty: {err}");
+        }
+
+        if tracing::enabled!(tracing::Level::TRACE) {
+            let grid = self.term.grid();
+            for y in 0..grid.rows() {
+                tracing::trace!("{y:2}|{}", grid.row_text(y));
+            }
+        }
+
+        if self.term.title() != self.title.as_deref() {
+            self.title = self.term.title().map(str::to_owned);
+            self.window
+                .set_title(self.title.clone().unwrap_or_default());
+        }
+    }
+
     /// The child shell has gone away; reap it and tear the window down.
     fn child_exited(&mut self) {
         match self.pty.wait() {