diff --git a/src/protocol.zig b/src/protocol.zig
index 8e1c8ad..5b7ac59 100644
--- a/src/protocol.zig
+++ b/src/protocol.zig
@@ -91,7 +91,20 @@ fn parseToolLog(log_line: []const u8) ?struct { name: []const u8, command: []con
 fn commandResponse(allocator: std.mem.Allocator, session: *session_mod.Session, command: []const u8) ![]u8 {
     if (std.mem.eql(u8, command, "move_left")) return dispatchAndRespond(allocator, session, .move_left);
     if (std.mem.eql(u8, command, "move_right")) return dispatchAndRespond(allocator, session, .move_right);
+    if (std.mem.eql(u8, command, "move_up")) return dispatchAndRespond(allocator, session, .move_up);
+    if (std.mem.eql(u8, command, "move_down")) return dispatchAndRespond(allocator, session, .move_down);
+    if (std.mem.eql(u8, command, "move_word_forward")) return dispatchAndRespond(allocator, session, .move_word_forward);
+    if (std.mem.eql(u8, command, "move_word_back")) return dispatchAndRespond(allocator, session, .move_word_back);
+    if (std.mem.eql(u8, command, "move_word_end")) return dispatchAndRespond(allocator, session, .move_word_end);
+    if (std.mem.eql(u8, command, "move_line_start")) return dispatchAndRespond(allocator, session, .move_line_start);
+    if (std.mem.eql(u8, command, "move_line_end")) return dispatchAndRespond(allocator, session, .move_line_end);
     if (std.mem.eql(u8, command, "delete_backward")) return dispatchAndRespond(allocator, session, .delete_backward);
+    if (std.mem.eql(u8, command, "delete_forward")) return dispatchAndRespond(allocator, session, .delete_forward);
+    if (std.mem.eql(u8, command, "delete_line")) return dispatchAndRespond(allocator, session, .delete_line);
+    if (std.mem.eql(u8, command, "change_line")) return dispatchAndRespond(allocator, session, .change_line);
+    if (std.mem.eql(u8, command, "open_line_below")) return dispatchAndRespond(allocator, session, .open_line_below);
+    if (std.mem.eql(u8, command, "open_line_above")) return dispatchAndRespond(allocator, session, .open_line_above);
+    if (std.mem.startsWith(u8, command, "replace_char ")) return dispatchAndRespond(allocator, session, .{ .replace_char = command[13..] });
     if (std.mem.startsWith(u8, command, "insert ")) return dispatchAndRespond(allocator, session, .{ .insert = command[7..] });
     if (std.mem.startsWith(u8, command, "panel_open ")) return panelRespond(allocator, session, .{ .open = command[11..] });
     if (std.mem.startsWith(u8, command, "list_open ")) return listOpenRespond(allocator, session, command[10..]);
diff --git a/src/session.zig b/src/session.zig
index 7e78fe5..919c80c 100644
--- a/src/session.zig
+++ b/src/session.zig
@@ -26,9 +26,22 @@ pub const Pair = struct {
 pub const Command = union(enum) {
     move_left,
     move_right,
+    move_up,
+    move_down,
+    move_word_forward,
+    move_word_back,
+    move_word_end,
     insert: []const u8,
     insert_pair: Pair,
     delete_backward,
+    delete_forward,
+    delete_line,
+    change_line,
+    open_line_below,
+    open_line_above,
+    replace_char: []const u8,
+    move_line_start,
+    move_line_end,
 };
 
 pub const Snapshot = struct {
@@ -74,9 +87,22 @@ pub const Buffer = struct {
         switch (command) {
             .move_left => self.moveLeft(),
             .move_right => self.moveRight(),
+            .move_up => self.moveUp(),
+            .move_down => self.moveDown(),
+            .move_word_forward => self.moveWordForward(),
+            .move_word_back => self.moveWordBack(),
+            .move_word_end => self.moveWordEnd(),
             .insert => |text| try self.insert(text),
             .insert_pair => |pair| try self.insertPair(pair),
             .delete_backward => self.deleteBackward(),
+            .delete_forward => self.deleteForward(),
+            .delete_line => self.deleteLine(),
+            .change_line => try self.changeLine(),
+            .open_line_below => try self.openLineBelow(),
+            .open_line_above => try self.openLineAbove(),
+            .replace_char => |text| try self.replaceChar(text),
+            .move_line_start => self.moveLineStart(),
+            .move_line_end => self.moveLineEnd(),
         }
     }
 
@@ -90,6 +116,55 @@ pub const Buffer = struct {
         self.refreshCell();
     }
 
+    pub fn moveUp(self: *Buffer) void {
+        const current = self.currentLineRange(false);
+        if (current.start == 0) return;
+        const previous_end = current.start - 1;
+        var previous_start = previous_end;
+        while (previous_start > 0 and self.bytes.items[previous_start - 1] != '\n') previous_start -= 1;
+        self.cursor.byte = byteForCell(self.bytes.items, previous_start, previous_end, self.cursor.cell);
+        self.refreshCell();
+    }
+
+    pub fn moveDown(self: *Buffer) void {
+        const current = self.currentLineRange(false);
+        if (current.end >= self.bytes.items.len) return;
+        const next_start = current.end + 1;
+        if (next_start > self.bytes.items.len) return;
+        var next_end = next_start;
+        while (next_end < self.bytes.items.len and self.bytes.items[next_end] != '\n') next_end += 1;
+        self.cursor.byte = byteForCell(self.bytes.items, next_start, next_end, self.cursor.cell);
+        self.refreshCell();
+    }
+
+    pub fn moveWordForward(self: *Buffer) void {
+        var at = self.cursor.byte;
+        while (at < self.bytes.items.len and !isWordSeparator(self.bytes.items[at])) at = nextBoundary(self.bytes.items, at);
+        while (at < self.bytes.items.len and isWordSeparator(self.bytes.items[at])) at = nextBoundary(self.bytes.items, at);
+        self.cursor.byte = at;
+        self.refreshCell();
+    }
+
+    pub fn moveWordBack(self: *Buffer) void {
+        var at = self.cursor.byte;
+        while (at > 0 and isWordSeparator(self.bytes.items[previousBoundary(self.bytes.items, at)])) at = previousBoundary(self.bytes.items, at);
+        while (at > 0 and !isWordSeparator(self.bytes.items[previousBoundary(self.bytes.items, at)])) at = previousBoundary(self.bytes.items, at);
+        self.cursor.byte = at;
+        self.refreshCell();
+    }
+
+    pub fn moveWordEnd(self: *Buffer) void {
+        var at = self.cursor.byte;
+        while (at < self.bytes.items.len and isWordSeparator(self.bytes.items[at])) at = nextBoundary(self.bytes.items, at);
+        while (at < self.bytes.items.len) {
+            const next = nextBoundary(self.bytes.items, at);
+            if (next >= self.bytes.items.len or isWordSeparator(self.bytes.items[next])) break;
+            at = next;
+        }
+        self.cursor.byte = at;
+        self.refreshCell();
+    }
+
     pub fn insert(self: *Buffer, text: []const u8) !void {
         if (!std.unicode.utf8ValidateSlice(text)) return error.InvalidUtf8Insertion;
         try self.bytes.insertSlice(self.allocator, self.cursor.byte, text);
@@ -117,6 +192,76 @@ pub const Buffer = struct {
         self.selection = null;
     }
 
+    pub fn deleteForward(self: *Buffer) void {
+        if (self.cursor.byte >= self.bytes.items.len) return;
+        const end = nextBoundary(self.bytes.items, self.cursor.byte);
+        self.bytes.replaceRangeAssumeCapacity(self.cursor.byte, end - self.cursor.byte, "");
+        self.refreshCell();
+        self.selection = null;
+    }
+
+    pub fn replaceChar(self: *Buffer, text: []const u8) !void {
+        if (!std.unicode.utf8ValidateSlice(text)) return error.InvalidUtf8Insertion;
+        if (self.cursor.byte < self.bytes.items.len) self.deleteForward();
+        try self.insert(text);
+        self.moveLeft();
+    }
+
+    pub fn deleteLine(self: *Buffer) void {
+        const range = self.currentLineRange(true);
+        self.bytes.replaceRangeAssumeCapacity(range.start, range.end - range.start, "");
+        self.cursor.byte = @min(range.start, self.bytes.items.len);
+        self.refreshCell();
+        self.selection = null;
+    }
+
+    pub fn changeLine(self: *Buffer) !void {
+        const range = self.currentLineRange(false);
+        self.bytes.replaceRangeAssumeCapacity(range.start, range.end - range.start, "");
+        self.cursor.byte = @min(range.start, self.bytes.items.len);
+        self.refreshCell();
+        self.selection = null;
+    }
+
+    pub fn openLineBelow(self: *Buffer) !void {
+        const range = self.currentLineRange(false);
+        const has_line_break = range.end < self.bytes.items.len and self.bytes.items[range.end] == '\n';
+        const at = if (has_line_break) range.end + 1 else self.bytes.items.len;
+        try self.bytes.insertSlice(self.allocator, at, "\n");
+        self.cursor.byte = if (has_line_break) at else at + 1;
+        self.refreshCell();
+        self.selection = null;
+    }
+
+    pub fn openLineAbove(self: *Buffer) !void {
+        const range = self.currentLineRange(false);
+        try self.bytes.insertSlice(self.allocator, range.start, "\n");
+        self.cursor.byte = range.start;
+        self.refreshCell();
+        self.selection = null;
+    }
+
+    pub fn moveLineStart(self: *Buffer) void {
+        self.cursor.byte = self.currentLineRange(false).start;
+        self.refreshCell();
+    }
+
+    pub fn moveLineEnd(self: *Buffer) void {
+        self.cursor.byte = self.currentLineRange(false).end;
+        self.refreshCell();
+    }
+
+    const LineRange = struct { start: usize, end: usize };
+
+    fn currentLineRange(self: *const Buffer, include_newline: bool) LineRange {
+        var start = self.cursor.byte;
+        while (start > 0 and self.bytes.items[start - 1] != '\n') start -= 1;
+        var end = self.cursor.byte;
+        while (end < self.bytes.items.len and self.bytes.items[end] != '\n') end += 1;
+        if (include_newline and end < self.bytes.items.len and self.bytes.items[end] == '\n') end += 1;
+        return .{ .start = start, .end = end };
+    }
+
     fn refreshCell(self: *Buffer) void {
         self.cursor.cell = cellWidth(self.bytes.items[0..self.cursor.byte]);
     }
@@ -227,6 +372,23 @@ pub const Session = struct {
     }
 };
 
+fn isWordSeparator(byte: u8) bool {
+    return std.ascii.isWhitespace(byte) or std.mem.indexOfScalar(u8, "(){}[]<>.,;:+-*/=\"'`", byte) != null;
+}
+
+fn byteForCell(bytes: []const u8, start: usize, end: usize, target_cell: usize) usize {
+    var at = start;
+    var best = start;
+    while (at < end) {
+        const rel = cellWidth(bytes[start..at]);
+        if (rel > target_cell) break;
+        best = at;
+        at = nextBoundary(bytes, at);
+    }
+    if (cellWidth(bytes[start..@min(at, end)]) <= target_cell) return @min(at, end);
+    return best;
+}
+
 pub fn boundaryAtOrBefore(bytes: []const u8, cursor: usize) usize {
     var i = @min(cursor, bytes.len);
     if (i == bytes.len) return i;
@@ -441,3 +603,52 @@ test "adversarial: session panel operations fail clearly on empty or invalid sta
     const snap = try session.snapshot();
     try std.testing.expectEqual(@as(usize, 0), snap.panel_depth);
 }
+
+test "regular: buffer moves by line word and line edges" {
+    var buffer = try Buffer.openFromBytes(std.testing.allocator, "one\nab cd\nxy");
+    defer buffer.deinit();
+
+    buffer.moveDown();
+    try std.testing.expectEqual(@as(usize, 4), buffer.cursor.byte);
+    buffer.moveRight();
+    buffer.moveRight();
+    buffer.moveDown();
+    try std.testing.expectEqual(@as(usize, 12), buffer.cursor.byte);
+    buffer.moveUp();
+    try std.testing.expectEqual(@as(usize, 9), buffer.cursor.byte);
+    buffer.moveLineStart();
+    try std.testing.expectEqual(@as(usize, 4), buffer.cursor.byte);
+    buffer.moveWordForward();
+    try std.testing.expectEqual(@as(usize, 7), buffer.cursor.byte);
+    buffer.moveWordEnd();
+    try std.testing.expectEqual(@as(usize, 8), buffer.cursor.byte);
+    buffer.moveWordBack();
+    try std.testing.expectEqual(@as(usize, 7), buffer.cursor.byte);
+    buffer.moveLineEnd();
+    try std.testing.expectEqual(@as(usize, 9), buffer.cursor.byte);
+}
+
+test "regular: buffer line operations replace delete and open around utf8" {
+    var buffer = try Buffer.openFromBytes(std.testing.allocator, "éx\nsecond");
+    defer buffer.deinit();
+
+    try buffer.replaceChar("A");
+    var snap = buffer.snapshot();
+    try std.testing.expectEqualStrings("Ax\nsecond", snap.bytes);
+    try std.testing.expectEqual(@as(usize, 0), snap.cursor_byte);
+
+    try buffer.openLineBelow();
+    try buffer.insert("below");
+    snap = buffer.snapshot();
+    try std.testing.expectEqualStrings("Ax\nbelow\nsecond", snap.bytes);
+
+    buffer.moveLineStart();
+    try buffer.changeLine();
+    try buffer.insert("changed");
+    snap = buffer.snapshot();
+    try std.testing.expectEqualStrings("Ax\nchanged\nsecond", snap.bytes);
+
+    buffer.deleteLine();
+    snap = buffer.snapshot();
+    try std.testing.expectEqualStrings("Ax\nsecond", snap.bytes);
+}
diff --git a/src/tui.zig b/src/tui.zig
index 86bd5fb..c4f92a5 100644
--- a/src/tui.zig
+++ b/src/tui.zig
@@ -34,6 +34,15 @@ const PrefixRail = enum {
     match,
     go,
     repeat,
+    delete,
+    change,
+    yank,
+    replace,
+};
+
+const EditSnapshot = struct {
+    bytes: []u8,
+    cursor_byte: usize,
 };
 
 pub const Error = error{
@@ -116,6 +125,9 @@ pub const Client = struct {
     prefix: PrefixRail = .none,
     pending_count: usize = 0,
     last_rail: PrefixRail = .none,
+    undo_stack: std.ArrayList(EditSnapshot) = .empty,
+    redo_stack: std.ArrayList(EditSnapshot) = .empty,
+    yank_bytes: ?[]u8 = null,
 
     pub fn init(allocator: std.mem.Allocator, viewport: Viewport) !Client {
         return initWithIo(allocator, viewport, null);
@@ -135,6 +147,9 @@ pub const Client = struct {
 
     pub fn deinit(self: *Client) void {
         if (self.saved_bytes) |bytes| self.allocator.free(bytes);
+        if (self.yank_bytes) |bytes| self.allocator.free(bytes);
+        self.freeSnapshotStack(&self.undo_stack);
+        self.freeSnapshotStack(&self.redo_stack);
         self.repo.deinit();
         self.leader.deinit();
         self.session.deinit();
@@ -206,7 +221,7 @@ pub const Client = struct {
         if (std.mem.startsWith(u8, line, "insert ")) return self.applyProtocolCommand(line);
         if (std.mem.eql(u8, line, "left")) return self.applyProtocol("command move_left");
         if (std.mem.eql(u8, line, "right")) return self.applyProtocol("command move_right");
-        if (std.mem.eql(u8, line, "backspace")) return self.applyProtocol("command delete_backward");
+        if (std.mem.eql(u8, line, "backspace")) return self.applyMutatingProtocol("command delete_backward");
         if (std.mem.eql(u8, line, "save")) return self.save();
         if (std.mem.startsWith(u8, line, "resize ")) return self.resize(line[7..]);
         if (std.mem.eql(u8, line, "render")) return;
@@ -400,6 +415,10 @@ pub const Client = struct {
             .match => "match: m jump  s inside  a around  ( { [ quotes",
             .go => "go: d definition  r references  e diagnostic  a parameter",
             .repeat => "repeat: digits count  . repeat-last",
+            .delete => "delete: d line  h previous-char  l char",
+            .change => "change: c line  h previous-char  l char",
+            .yank => "yank: y line",
+            .replace => "replace: next key replaces char",
         };
     }
 
@@ -735,26 +754,51 @@ pub const Client = struct {
                     self.pending_count = 0;
                     return;
                 }
+                if (std.mem.eql(u8, text, "a")) {
+                    try self.applyProtocol("command move_right");
+                    self.mode = .insert;
+                    self.message = "insert";
+                    self.pending_count = 0;
+                    return;
+                }
+                if (std.mem.eql(u8, text, "o")) {
+                    try self.applyMutatingProtocol("command open_line_below");
+                    self.mode = .insert;
+                    self.message = "insert";
+                    self.pending_count = 0;
+                    return;
+                }
+                if (std.mem.eql(u8, text, "O")) {
+                    try self.applyMutatingProtocol("command open_line_above");
+                    self.mode = .insert;
+                    self.message = "insert";
+                    self.pending_count = 0;
+                    return;
+                }
                 if (std.mem.eql(u8, text, "s")) {
                     self.mode = .select;
                     self.message = "select";
                     self.pending_count = 0;
                     return;
                 }
+                if (std.mem.eql(u8, text, "d")) return self.openPrefix(.delete);
+                if (std.mem.eql(u8, text, "c")) return self.openPrefix(.change);
+                if (std.mem.eql(u8, text, "y")) return self.openPrefix(.yank);
+                if (std.mem.eql(u8, text, "r")) return self.openPrefix(.replace);
+                if (std.mem.eql(u8, text, "p")) return self.pasteRegister();
+                if (std.mem.eql(u8, text, "u")) return self.undoEdit();
+                if (std.mem.eql(u8, text, "U")) return self.redoEdit();
+                if (std.mem.eql(u8, text, "0")) return self.applyProtocol("command move_line_start");
+                if (std.mem.eql(u8, text, "$")) return self.applyProtocol("command move_line_end");
                 if (std.mem.eql(u8, text, "m")) return self.openPrefix(.match);
                 if (std.mem.eql(u8, text, "g")) return self.openPrefix(.go);
-                if (std.mem.eql(u8, text, "j")) {
-                    _ = self.takeRepeat();
-                    self.message = "vertical movement is not built in this profile yet";
-                    return;
-                }
-                if (std.mem.eql(u8, text, "k")) {
-                    _ = self.takeRepeat();
-                    self.message = "vertical movement is not built in this profile yet";
-                    return;
-                }
+                if (std.mem.eql(u8, text, "j")) return self.repeatProtocol("command move_down", self.takeRepeat());
+                if (std.mem.eql(u8, text, "k")) return self.repeatProtocol("command move_up", self.takeRepeat());
                 if (std.mem.eql(u8, text, "h")) return self.repeatProtocol("command move_left", self.takeRepeat());
                 if (std.mem.eql(u8, text, "l")) return self.repeatProtocol("command move_right", self.takeRepeat());
+                if (std.mem.eql(u8, text, "w")) return self.repeatProtocol("command move_word_forward", self.takeRepeat());
+                if (std.mem.eql(u8, text, "b")) return self.repeatProtocol("command move_word_back", self.takeRepeat());
+                if (std.mem.eql(u8, text, "e")) return self.repeatProtocol("command move_word_end", self.takeRepeat());
                 self.unknownPrefixOrInput("normal");
             },
             .key => |key| switch (key) {
@@ -762,13 +806,11 @@ pub const Client = struct {
                     self.pending_count = 0;
                     self.message = "normal";
                 },
-                .backspace => try self.applyProtocol("command delete_backward"),
+                .backspace => try self.applyMutatingProtocol("command delete_backward"),
                 .arrow_left => try self.repeatProtocol("command move_left", self.takeRepeat()),
                 .arrow_right => try self.repeatProtocol("command move_right", self.takeRepeat()),
-                .arrow_up, .arrow_down => {
-                    _ = self.takeRepeat();
-                    self.message = "vertical movement is not built in this profile yet";
-                },
+                .arrow_up => try self.repeatProtocol("command move_up", self.takeRepeat()),
+                .arrow_down => try self.repeatProtocol("command move_down", self.takeRepeat()),
                 else => self.unknownPrefixOrInput("normal"),
             },
             .unknown => self.unknownPrefixOrInput("normal"),
@@ -784,7 +826,7 @@ pub const Client = struct {
                     self.mode = .normal;
                     self.message = "normal";
                 },
-                .backspace => try self.applyProtocol("command delete_backward"),
+                .backspace => try self.applyMutatingProtocol("command delete_backward"),
                 .arrow_left => try self.applyProtocol("command move_left"),
                 .arrow_right => try self.applyProtocol("command move_right"),
                 else => {},
@@ -848,6 +890,10 @@ pub const Client = struct {
             .match => self.applyKnownRailOrMessage(event, "match rail ready"),
             .go => self.applyKnownRailOrMessage(event, "go rail ready"),
             .repeat => self.applyKnownRailOrMessage(event, "repeat rail ready"),
+            .delete => try self.applyDeleteRail(event),
+            .change => try self.applyChangeRail(event),
+            .yank => try self.applyYankRail(event),
+            .replace => try self.applyReplaceRail(event),
         }
     }
 
@@ -908,10 +954,146 @@ pub const Client = struct {
         self.message = null;
     }
 
+    fn applyDeleteRail(self: *Client, event: input.Event) !void {
+        const text = eventText(event) orelse return self.unknownPrefixOrInput("normal");
+        if (std.mem.eql(u8, text, "d")) {
+            try self.yankCurrentLine(true);
+            try self.applyMutatingProtocol("command delete_line");
+            return;
+        }
+        if (std.mem.eql(u8, text, "h")) return self.applyMutatingProtocol("command delete_backward");
+        if (std.mem.eql(u8, text, "l")) return self.applyMutatingProtocol("command delete_forward");
+        self.unknownPrefixOrInput("normal");
+    }
+
+    fn applyChangeRail(self: *Client, event: input.Event) !void {
+        const text = eventText(event) orelse return self.unknownPrefixOrInput("normal");
+        if (std.mem.eql(u8, text, "c")) {
+            try self.yankCurrentLine(false);
+            try self.applyMutatingProtocol("command change_line");
+            self.mode = .insert;
+            self.message = "insert";
+            return;
+        }
+        if (std.mem.eql(u8, text, "h")) {
+            try self.applyMutatingProtocol("command delete_backward");
+            self.mode = .insert;
+            self.message = "insert";
+            return;
+        }
+        if (std.mem.eql(u8, text, "l")) {
+            try self.applyMutatingProtocol("command delete_forward");
+            self.mode = .insert;
+            self.message = "insert";
+            return;
+        }
+        self.unknownPrefixOrInput("normal");
+    }
+
+    fn applyYankRail(self: *Client, event: input.Event) !void {
+        const text = eventText(event) orelse return self.unknownPrefixOrInput("normal");
+        if (std.mem.eql(u8, text, "y")) {
+            try self.yankCurrentLine(true);
+            self.message = "yanked line";
+            return;
+        }
+        self.unknownPrefixOrInput("normal");
+    }
+
+    fn applyReplaceRail(self: *Client, event: input.Event) !void {
+        const text = eventText(event) orelse return self.unknownPrefixOrInput("normal");
+        const command = try std.fmt.allocPrint(self.allocator, "command replace_char {s}", .{text});
+        defer self.allocator.free(command);
+        try self.applyMutatingProtocol(command);
+    }
+
+    fn eventText(event: input.Event) ?[]const u8 {
+        return switch (event) {
+            .text => |text| text,
+            .key => |key| switch (key) {
+                .space => " ",
+                else => null,
+            },
+            .unknown => null,
+        };
+    }
+
+    fn pasteRegister(self: *Client) !void {
+        const bytes = self.yank_bytes orelse {
+            self.message = "nothing yanked";
+            return;
+        };
+        try self.recordUndo();
+        self.clearRedo();
+        self.session.dispatch(.{ .insert = bytes }) catch |err| {
+            self.dropLastUndoSnapshot();
+            return err;
+        };
+    }
+
+    fn yankCurrentLine(self: *Client, include_newline: bool) !void {
+        const snap = try self.session.snapshot();
+        var start = snap.cursor_byte;
+        while (start > 0 and snap.bytes[start - 1] != '\n') start -= 1;
+        var end = snap.cursor_byte;
+        while (end < snap.bytes.len and snap.bytes[end] != '\n') end += 1;
+        if (include_newline and end < snap.bytes.len and snap.bytes[end] == '\n') end += 1;
+        const copy = try self.allocator.dupe(u8, snap.bytes[start..end]);
+        if (self.yank_bytes) |old| self.allocator.free(old);
+        self.yank_bytes = copy;
+    }
+
+    fn undoEdit(self: *Client) !void {
+        const previous = self.undo_stack.pop() orelse {
+            self.message = "nothing to undo";
+            return;
+        };
+        const current = try self.takeCurrentSnapshot();
+        try self.redo_stack.append(self.allocator, current);
+        try self.restoreSnapshot(previous);
+        self.allocator.free(previous.bytes);
+        self.message = "undo";
+    }
+
+    fn redoEdit(self: *Client) !void {
+        const next = self.redo_stack.pop() orelse {
+            self.message = "nothing to redo";
+            return;
+        };
+        const current = try self.takeCurrentSnapshot();
+        try self.undo_stack.append(self.allocator, current);
+        try self.restoreSnapshot(next);
+        self.allocator.free(next.bytes);
+        self.message = "redo";
+    }
+
+    fn takeCurrentSnapshot(self: *Client) !EditSnapshot {
+        const snap = try self.session.snapshot();
+        return .{ .bytes = try self.allocator.dupe(u8, snap.bytes), .cursor_byte = snap.cursor_byte };
+    }
+
     fn insertText(self: *Client, text: []const u8) !void {
         const line = try std.fmt.allocPrint(self.allocator, "insert {s}", .{text});
         defer self.allocator.free(line);
-        try self.applyProtocolCommand(line);
+        try self.applyMutatingProtocolCommand(line);
+    }
+
+    fn applyMutatingProtocolCommand(self: *Client, line: []const u8) !void {
+        try self.recordUndo();
+        self.clearRedo();
+        self.applyProtocolCommand(line) catch |err| {
+            self.dropLastUndoSnapshot();
+            return err;
+        };
+    }
+
+    fn applyMutatingProtocol(self: *Client, line: []const u8) !void {
+        try self.recordUndo();
+        self.clearRedo();
+        self.applyProtocol(line) catch |err| {
+            self.dropLastUndoSnapshot();
+            return err;
+        };
     }
 
     fn repeatProtocol(self: *Client, line: []const u8, repeat: usize) !void {
@@ -919,6 +1101,39 @@ pub const Client = struct {
         while (i < repeat) : (i += 1) try self.applyProtocol(line);
     }
 
+    fn repeatMutatingProtocol(self: *Client, line: []const u8, repeat: usize) !void {
+        var i: usize = 0;
+        while (i < repeat) : (i += 1) try self.applyMutatingProtocol(line);
+    }
+
+    fn recordUndo(self: *Client) !void {
+        const snap = try self.session.snapshot();
+        const bytes = try self.allocator.dupe(u8, snap.bytes);
+        errdefer self.allocator.free(bytes);
+        try self.undo_stack.append(self.allocator, .{
+            .bytes = bytes,
+            .cursor_byte = snap.cursor_byte,
+        });
+    }
+
+    fn dropLastUndoSnapshot(self: *Client) void {
+        if (self.undo_stack.pop()) |snap| self.allocator.free(snap.bytes);
+    }
+
+    fn restoreSnapshot(self: *Client, snap: EditSnapshot) !void {
+        try self.session.openFixtureAt(snap.bytes, snap.cursor_byte);
+    }
+
+    fn freeSnapshotStack(self: *Client, stack: *std.ArrayList(EditSnapshot)) void {
+        for (stack.items) |snap| self.allocator.free(snap.bytes);
+        stack.deinit(self.allocator);
+    }
+
+    fn clearRedo(self: *Client) void {
+        self.freeSnapshotStack(&self.redo_stack);
+        self.redo_stack = .empty;
+    }
+
     fn unknownPrefixOrInput(self: *Client, mode: []const u8) void {
         self.pending_count = 0;
         self.message = if (std.mem.eql(u8, mode, "normal"))
@@ -2448,3 +2663,89 @@ test "regular: insert pending space commits literal space or returns normal" {
     try client.handleInput("n");
     try std.testing.expectEqualStrings("normal", client.modeName());
 }
+
+test "regular: normal core editing delete yank paste undo redo" {
+    var client = try Client.init(std.testing.allocator, .{ .width = 48, .height = 8 });
+    defer client.deinit();
+    try client.handleTraceLine("open abc\ndef");
+
+    try client.handleInput("d");
+    try client.handleInput("d");
+    const after_delete = try client.snapshotBytesAlloc(std.testing.allocator);
+    defer std.testing.allocator.free(after_delete);
+    try std.testing.expectEqualStrings("def", after_delete);
+
+    try client.handleInput("p");
+    const after_paste = try client.snapshotBytesAlloc(std.testing.allocator);
+    defer std.testing.allocator.free(after_paste);
+    try std.testing.expectEqualStrings("abc\ndef", after_paste);
+
+    try client.handleInput("u");
+    const after_undo = try client.snapshotBytesAlloc(std.testing.allocator);
+    defer std.testing.allocator.free(after_undo);
+    try std.testing.expectEqualStrings("def", after_undo);
+
+    try client.handleInput("U");
+    const after_redo = try client.snapshotBytesAlloc(std.testing.allocator);
+    defer std.testing.allocator.free(after_redo);
+    try std.testing.expectEqualStrings("abc\ndef", after_redo);
+}
+
+test "regular: normal change replace open lines and movement enter insert" {
+    var client = try Client.init(std.testing.allocator, .{ .width = 48, .height = 8 });
+    defer client.deinit();
+    try client.handleTraceLine("open abc\ndef");
+
+    try client.handleInput("r");
+    try client.handleInput("Z");
+    const after_replace = try client.snapshotBytesAlloc(std.testing.allocator);
+    defer std.testing.allocator.free(after_replace);
+    try std.testing.expectEqualStrings("Zbc\ndef", after_replace);
+
+    try client.handleInput("c");
+    try client.handleInput("c");
+    try std.testing.expectEqualStrings("insert", client.modeName());
+    try client.handleInput("X");
+    try client.handleInput(" ");
+    try client.handleInput("n");
+    const after_change = try client.snapshotBytesAlloc(std.testing.allocator);
+    defer std.testing.allocator.free(after_change);
+    try std.testing.expectEqualStrings("X\ndef", after_change);
+
+    try client.handleInput("o");
+    try client.handleInput("Y");
+    try client.handleInput(" ");
+    try client.handleInput("n");
+    const after_open = try client.snapshotBytesAlloc(std.testing.allocator);
+    defer std.testing.allocator.free(after_open);
+    try std.testing.expectEqualStrings("X\nY\ndef", after_open);
+
+    try client.handleInput("0");
+    try client.handleInput("l");
+    try client.handleInput("k");
+    try client.handleInput("w");
+    try client.handleInput("e");
+    try client.handleInput("b");
+}
+
+test "adversarial: replace rejects invalid utf8 and undo preserves content" {
+    var client = try Client.init(std.testing.allocator, .{ .width = 48, .height = 8 });
+    defer client.deinit();
+    try client.handleTraceLine("open safe");
+
+    const bad = [_]u8{ 0xc3, 0x28 };
+    try client.handleInput("r");
+    try client.handleInput(&bad);
+    const after_bad_replace = try client.snapshotBytesAlloc(std.testing.allocator);
+    defer std.testing.allocator.free(after_bad_replace);
+    try std.testing.expectEqualStrings("safe", after_bad_replace);
+
+    try client.handleInput("i");
+    try client.handleInput("!");
+    try client.handleInput(" ");
+    try client.handleInput("n");
+    try client.handleInput("u");
+    const after_undo = try client.snapshotBytesAlloc(std.testing.allocator);
+    defer std.testing.allocator.free(after_undo);
+    try std.testing.expectEqualStrings("safe", after_undo);
+}