diff --git a/rust/crates/rusty-claude-cli/src/chat_mode.rs b/rust/crates/rusty-claude-cli/src/chat_mode.rs
new file mode 100644
index 00000000..45022781
--- /dev/null
+++ b/rust/crates/rusty-claude-cli/src/chat_mode.rs
@@ -0,0 +1,83 @@
+//! Chat mode — controls AI behavior (code/ask/architect).
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum ChatMode {
+    /// Default — full access, edits files and runs commands.
+    Code,
+    /// Discussion only — no file changes.
+    Ask,
+    /// Plan first, then implement after approval.
+    Architect,
+}
+
+impl ChatMode {
+    pub fn label(&self) -> &'static str {
+        match self {
+            ChatMode::Code => "code",
+            ChatMode::Ask => "ask",
+            ChatMode::Architect => "arch",
+        }
+    }
+
+    pub fn description(&self) -> &'static str {
+        match self {
+            ChatMode::Code => "Full access — edits and runs code",
+            ChatMode::Ask => "Discussion only — no changes made",
+            ChatMode::Architect => "Plan first, then implement",
+        }
+    }
+
+    /// Appended to system prompt to instruct the model about mode constraints.
+    pub fn system_prompt_suffix(&self) -> &'static str {
+        match self {
+            ChatMode::Code => "",
+            ChatMode::Ask => "\n\nIMPORTANT: Do NOT modify any files. Only discuss and explain.",
+            ChatMode::Architect => {
+                "\n\nIMPORTANT: First create a plan. After the user approves, implement it."
+            }
+        }
+    }
+
+    /// Cycle to the next mode.
+    pub fn next(self) -> Self {
+        match self {
+            ChatMode::Code => ChatMode::Ask,
+            ChatMode::Ask => ChatMode::Architect,
+            ChatMode::Architect => ChatMode::Code,
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_cycle() {
+        assert_eq!(ChatMode::Code.next(), ChatMode::Ask);
+        assert_eq!(ChatMode::Ask.next(), ChatMode::Architect);
+        assert_eq!(ChatMode::Architect.next(), ChatMode::Code);
+    }
+
+    #[test]
+    fn test_labels() {
+        assert_eq!(ChatMode::Code.label(), "code");
+        assert_eq!(ChatMode::Ask.label(), "ask");
+        assert_eq!(ChatMode::Architect.label(), "arch");
+    }
+
+    #[test]
+    fn test_code_mode_has_no_suffix() {
+        assert_eq!(ChatMode::Code.system_prompt_suffix(), "");
+    }
+
+    #[test]
+    fn test_ask_mode_restrains() {
+        assert!(ChatMode::Ask.system_prompt_suffix().contains("Do NOT modify"));
+    }
+
+    #[test]
+    fn test_architect_mode_plans_first() {
+        assert!(ChatMode::Architect.system_prompt_suffix().contains("plan"));
+    }
+}
diff --git a/rust/crates/rusty-claude-cli/src/main.rs b/rust/crates/rusty-claude-cli/src/main.rs
index 1636d8b1..ab42a55c 100644
--- a/rust/crates/rusty-claude-cli/src/main.rs
+++ b/rust/crates/rusty-claude-cli/src/main.rs
@@ -18,6 +18,7 @@ mod init;
 mod input;
 mod render;
 mod setup_wizard;
+mod chat_mode;
 mod command_palette;
 mod keybindings;
 mod markdown;
@@ -7181,6 +7182,112 @@ fn run_tui_repl(mut cli: LiveCli) -> Result<(), Box<dyn std::error::Error>> {
                     break;
                 }
 
+                // Slash commands handled locally in TUI (not sent to model)
+                if trimmed.starts_with("/theme") {
+                    let args = trimmed.strip_prefix("/theme").unwrap_or("").trim();
+                    if args.is_empty() {
+                        let names = crate::theme::TuiTheme::all_builtin_names();
+                        app.push_system_message(&format!(
+                            "Available themes: {}\nUsage: /theme <name>",
+                            names.join(", ")
+                        ));
+                    } else if let Some(theme) = crate::theme::TuiTheme::builtin(args) {
+                        app.set_theme(theme);
+                        app.push_system_message(&format!("Theme: {args}"));
+                    } else {
+                        app.push_system_message(&format!("Unknown theme: {args}"));
+                    }
+                    continue;
+                }
+                if trimmed.starts_with("/keys") {
+                    let args = trimmed.strip_prefix("/keys").unwrap_or("").trim();
+                    match args {
+                        "emacs" => { app.keymap.set_preset(crate::keybindings::KeyPreset::Emacs); app.push_system_message("Keys: Emacs"); }
+                        "vim" => { app.keymap.set_preset(crate::keybindings::KeyPreset::Vim); app.push_system_message("Keys: Vim — i for insert, Esc for normal"); }
+                        "windows" => { app.keymap.set_preset(crate::keybindings::KeyPreset::Windows); app.push_system_message("Keys: Windows"); }
+                        "" => {
+                            app.push_system_message(&format!("Current: {:?}\nAvailable: emacs, vim, windows\nUsage: /keys <preset>", app.keymap.preset()));
+                        }
+                        _ => { app.push_system_message(&format!("Unknown: {args}. Available: emacs, vim, windows")); }
+                    }
+                    continue;
+                }
+                if matches!(trimmed.as_str(), "/code" | "/ask" | "/architect" | "/arch") {
+                    let mode = match trimmed.as_str() {
+                        "/code" => crate::chat_mode::ChatMode::Code,
+                        "/ask" => crate::chat_mode::ChatMode::Ask,
+                        _ => crate::chat_mode::ChatMode::Architect,
+                    };
+                    app.chat_mode = mode;
+                    app.push_system_message(&format!("Mode: {} — {}", mode.label(), mode.description()));
+                    continue;
+                }
+                if trimmed == "/diff" {
+                    let output = std::process::Command::new("git")
+                        .args(["diff"])
+                        .current_dir(std::env::current_dir().unwrap_or_default())
+                        .output();
+                    match output {
+                        Ok(out) if out.status.success() => {
+                            let diff = String::from_utf8_lossy(&out.stdout);
+                            if diff.is_empty() {
+                                app.push_system_message("No uncommitted changes.");
+                            } else {
+                                app.push_diff(&diff);
+                            }
+                        }
+                        Ok(out) => {
+                            let err = String::from_utf8_lossy(&out.stderr);
+                            app.push_system_message(&format!("git diff failed: {err}"));
+                        }
+                        Err(e) => { app.push_system_message(&format!("Failed to run git: {e}")); }
+                    }
+                    continue;
+                }
+                if trimmed.starts_with("/undo") {
+                    let args = trimmed.strip_prefix("/undo").unwrap_or("").trim();
+                    if args == "--confirm" || args == "-y" {
+                        let output = std::process::Command::new("git")
+                            .args(["checkout", "--", "."])
+                            .current_dir(std::env::current_dir().unwrap_or_default())
+                            .output();
+                        match output {
+                            Ok(out) if out.status.success() => app.push_system_message("✓ Reverted all uncommitted changes."),
+                            Ok(out) => { let err = String::from_utf8_lossy(&out.stderr); app.push_system_message(&format!("Undo failed: {err}")); }
+                            Err(e) => { app.push_system_message(&format!("Failed to run git: {e}")); }
+                        }
+                    } else {
+                        let output = std::process::Command::new("git")
+                            .args(["diff", "--stat"])
+                            .current_dir(std::env::current_dir().unwrap_or_default())
+                            .output();
+                        let stat = output.ok().filter(|o| o.status.success())
+                            .map(|o| String::from_utf8_lossy(&o.stdout).to_string())
+                            .unwrap_or_default();
+                        if stat.is_empty() {
+                            app.push_system_message("Nothing to undo — no uncommitted changes.");
+                        } else {
+                            app.push_system_message(&format!("This will revert:\n{stat}\nType /undo --confirm to proceed."));
+                        }
+                    }
+                    continue;
+                }
+                if trimmed.starts_with("/ls") {
+                    let path = trimmed.strip_prefix("/ls").unwrap_or("").trim();
+                    if path.is_empty() {
+                        app.push_system_message("Usage: /ls <file-path>");
+                    } else {
+                        match std::fs::read_to_string(path) {
+                            Ok(content) => {
+                                app.push_system_message(&format!("── {path} ──"));
+                                app.push_output(&content, false);
+                            }
+                            Err(e) => app.push_system_message(&format!("Cannot read {path}: {e}")),
+                        }
+                    }
+                    continue;
+                }
+
                 app.push_user_input(&input);
                 cli.record_prompt_history(&trimmed);
                 update_dashboard(&dashboard_state, &cli);
diff --git a/rust/crates/rusty-claude-cli/src/tui.rs b/rust/crates/rusty-claude-cli/src/tui.rs
index bdfe6ae7..37734bb4 100644
--- a/rust/crates/rusty-claude-cli/src/tui.rs
+++ b/rust/crates/rusty-claude-cli/src/tui.rs
@@ -182,6 +182,7 @@ pub struct TuiApp {
     pub theme: crate::theme::TuiTheme,
     pub keymap: crate::keybindings::KeyMap,
     pub command_palette: crate::command_palette::CommandPalette,
+    pub chat_mode: crate::chat_mode::ChatMode,
 }
 
 const SPINNER_FRAMES: &[&str] = &["⠋", "⠙", "⠹", "⠸", "⠼", "⠴", "⠦", "⠧", "⠇", "⠏"];
@@ -238,6 +239,7 @@ impl TuiApp {
             theme: crate::theme::TuiTheme::builtin("default").unwrap(),
             keymap: crate::keybindings::KeyMap::new(crate::keybindings::KeyPreset::Emacs),
             command_palette: crate::command_palette::CommandPalette::new(),
+            chat_mode: crate::chat_mode::ChatMode::Code,
             needs_redraw: true,
         };
         me.draw_screen()?;