diff --git a/crates/tui/src/app.rs b/crates/tui/src/app.rs
index 15f1fb63..0326a19a 100644
--- a/crates/tui/src/app.rs
+++ b/crates/tui/src/app.rs
@@ -10,12 +10,21 @@ use crate::block::{
     Block, CompactEvent, ThinkingBlock, ThinkingState, ToolCallBlock, ToolCallState,
 };
 use crate::cache::FileCache;
-use crate::command::{CommandEnvironment, CommandExecution, CommandInputMode, CommandRegistry};
+use crate::command::{
+    CommandCandidate, CommandEnvironment, CommandExecution, CommandInputMode, CommandRegistry,
+};
 use crate::input::InputBuffer;
 use crate::scroll::Scroll;
 use crate::task::TaskStore;
 use crate::ui::Mode;
 
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum CommandCompletionApply {
+    Applied,
+    Ambiguous,
+    NoCandidates,
+}
+
 /// In-flight completion popup state. Lives on `App` while the user is
 /// typing inside a `@` / `#` / `/` token. Cleared whenever the trigger
 /// is invalidated (cursor moved out, whitespace landed inside the
@@ -99,6 +108,7 @@ pub struct App {
     pub command_input: InputBuffer,
     pub input_mode: CommandInputMode,
     pub command_registry: CommandRegistry,
+    command_completion_selected: Option<usize>,
     pub quit: bool,
     /// 2-tap guard for `Ctrl-C` when the Pod is not running. First press
     /// records the instant; a second press within the timeout exits the
@@ -158,6 +168,7 @@ impl App {
             command_input: InputBuffer::new(),
             input_mode: CommandInputMode::Composer,
             command_registry: CommandRegistry::default(),
+            command_completion_selected: None,
             quit: false,
             quit_confirm: None,
             blocks: Vec::new(),
@@ -1078,26 +1089,137 @@ impl App {
     pub fn enter_command_mode(&mut self) {
         self.input_mode = CommandInputMode::Command;
         self.completion = None;
+        self.command_completion_selected = None;
         self.quit_confirm = None;
     }
 
     pub fn exit_command_mode(&mut self) {
         self.input_mode = CommandInputMode::Composer;
         self.command_input.clear();
+        self.command_completion_selected = None;
     }
 
     pub fn clear_command_input(&mut self) {
         self.command_input.clear();
+        self.command_completion_selected = None;
     }
 
     pub fn command_text(&self) -> String {
         self.command_input.plain_text()
     }
 
-    pub fn command_suggestions(&self) -> Vec<crate::command::CommandCandidate> {
+    pub fn command_suggestions(&self) -> Vec<CommandCandidate> {
         self.command_registry.suggest(&self.command_text())
     }
 
+    pub fn command_completion_selected(&self) -> Option<usize> {
+        let selected = self.command_completion_selected?;
+        (selected < self.command_suggestions().len()).then_some(selected)
+    }
+
+    pub fn command_completion_active(&self) -> bool {
+        !self.command_suggestions().is_empty()
+    }
+
+    pub fn move_command_completion_up(&mut self) {
+        let len = self.command_suggestions().len();
+        if len == 0 {
+            self.command_completion_selected = None;
+            return;
+        }
+        self.command_completion_selected = Some(match self.command_completion_selected() {
+            Some(0) | None => len - 1,
+            Some(selected) => selected - 1,
+        });
+    }
+
+    pub fn move_command_completion_down(&mut self) {
+        let len = self.command_suggestions().len();
+        if len == 0 {
+            self.command_completion_selected = None;
+            return;
+        }
+        self.command_completion_selected = Some(match self.command_completion_selected() {
+            Some(selected) => (selected + 1) % len,
+            None => 0,
+        });
+    }
+
+    pub fn apply_command_completion(&mut self) -> CommandCompletionApply {
+        let suggestions = self.command_suggestions();
+        let candidate = match self.command_completion_selected() {
+            Some(selected) => suggestions.get(selected),
+            None if suggestions.len() == 1 => suggestions.first(),
+            None if suggestions.is_empty() => return CommandCompletionApply::NoCandidates,
+            None => return self.ambiguous_command_completion(),
+        };
+
+        let Some(candidate) = candidate else {
+            self.command_completion_selected = None;
+            return CommandCompletionApply::NoCandidates;
+        };
+        self.replace_command_name(candidate.name);
+        self.command_completion_selected = None;
+        CommandCompletionApply::Applied
+    }
+
+    pub fn submit_command_with_completion(&mut self) -> Option<Method> {
+        let selected = self.command_completion_selected().is_some();
+        let command_text = self.command_text();
+        if command_text.trim().is_empty() && !selected {
+            return self.submit_command();
+        }
+        if !selected && self.command_name_is_complete(&command_text) {
+            return self.submit_command();
+        }
+
+        match self.apply_command_completion() {
+            CommandCompletionApply::Applied | CommandCompletionApply::NoCandidates => {
+                self.submit_command()
+            }
+            CommandCompletionApply::Ambiguous => None,
+        }
+    }
+
+    fn ambiguous_command_completion(&mut self) -> CommandCompletionApply {
+        self.push_command_diagnostic(
+            "Ambiguous command completion; select a candidate with Up/Down or keep typing.",
+        );
+        CommandCompletionApply::Ambiguous
+    }
+
+    fn command_name_is_complete(&self, command_line: &str) -> bool {
+        let trimmed = command_line.trim_start();
+        let name = trimmed
+            .find(char::is_whitespace)
+            .map(|idx| &trimmed[..idx])
+            .unwrap_or(trimmed);
+        !name.is_empty() && self.command_registry.find(name).is_some()
+    }
+
+    fn replace_command_name(&mut self, canonical_name: &str) {
+        let command_line = self.command_text();
+        let leading_len = command_line.len() - command_line.trim_start().len();
+        let after_leading = &command_line[leading_len..];
+        let name_end = after_leading
+            .find(char::is_whitespace)
+            .map(|idx| leading_len + idx)
+            .unwrap_or(command_line.len());
+        let rest = &command_line[name_end..];
+
+        let mut completed = String::with_capacity(command_line.len().max(canonical_name.len() + 1));
+        completed.push_str(&command_line[..leading_len]);
+        completed.push_str(canonical_name);
+        if rest.is_empty() {
+            completed.push(' ');
+        } else {
+            completed.push_str(rest);
+        }
+
+        self.command_input.clear();
+        self.command_input.insert_str(&completed);
+    }
+
     fn command_environment(&self) -> CommandEnvironment {
         CommandEnvironment {
             connected: self.connected,
@@ -1119,9 +1241,11 @@ impl App {
         }
         if result.clear_input {
             self.command_input.clear();
+            self.command_completion_selected = None;
         }
         if result.exit_command_mode {
             self.input_mode = CommandInputMode::Composer;
+            self.command_completion_selected = None;
         }
         result.method
     }
@@ -1146,23 +1270,40 @@ impl App {
     // stay readable. In command mode these operate on the command line,
     // keeping the normal composer buffer intact.
     pub fn insert_char(&mut self, c: char) {
+        let command_mode = self.is_command_mode();
         self.active_input_mut().insert_char(c);
+        if command_mode {
+            self.command_completion_selected = None;
+        }
     }
     pub fn insert_newline(&mut self) {
+        let command_mode = self.is_command_mode();
         self.active_input_mut().insert_newline();
+        if command_mode {
+            self.command_completion_selected = None;
+        }
     }
     pub fn insert_paste(&mut self, content: String) {
         if self.is_command_mode() {
             self.command_input.insert_str(&content);
+            self.command_completion_selected = None;
         } else {
             self.input.insert_paste(content);
         }
     }
     pub fn delete_char_before(&mut self) {
+        let command_mode = self.is_command_mode();
         self.active_input_mut().delete_before();
+        if command_mode {
+            self.command_completion_selected = None;
+        }
     }
     pub fn delete_char_after(&mut self) {
+        let command_mode = self.is_command_mode();
         self.active_input_mut().delete_after();
+        if command_mode {
+            self.command_completion_selected = None;
+        }
     }
     pub fn move_cursor_left(&mut self) {
         self.active_input_mut().move_left();
diff --git a/crates/tui/src/main.rs b/crates/tui/src/main.rs
index 6d4d4f8a..15430301 100644
--- a/crates/tui/src/main.rs
+++ b/crates/tui/src/main.rs
@@ -992,7 +992,7 @@ fn handle_command_key(app: &mut App, key: KeyEvent) -> Option<Method> {
             app.exit_command_mode();
             None
         }
-        KeyCode::Enter => app.submit_command(),
+        KeyCode::Enter => app.submit_command_with_completion(),
         KeyCode::Backspace => {
             if app.command_text().is_empty() {
                 app.exit_command_mode();
@@ -1014,11 +1014,19 @@ fn handle_command_key(app: &mut App, key: KeyEvent) -> Option<Method> {
             None
         }
         KeyCode::Up => {
-            app.move_cursor_up();
+            if app.command_completion_active() {
+                app.move_command_completion_up();
+            } else {
+                app.move_cursor_up();
+            }
             None
         }
         KeyCode::Down => {
-            app.move_cursor_down();
+            if app.command_completion_active() {
+                app.move_command_completion_down();
+            } else {
+                app.move_cursor_down();
+            }
             None
         }
         KeyCode::Home => {
@@ -1029,7 +1037,10 @@ fn handle_command_key(app: &mut App, key: KeyEvent) -> Option<Method> {
             app.move_cursor_end();
             None
         }
-        KeyCode::Tab => None,
+        KeyCode::Tab => {
+            app.apply_command_completion();
+            None
+        }
         KeyCode::Char(c) => {
             if key
                 .modifiers
@@ -1558,6 +1569,204 @@ mod tests {
         assert_eq!(suggestions[0].name, "noop");
     }
 
+    #[test]
+    fn command_completion_tab_applies_unambiguous_candidate() {
+        let mut app = App::new("agent".to_string());
+        enter_command_mode(&mut app);
+        type_keys(&mut app, "no");
+
+        assert!(handle_key(&mut app, key(KeyCode::Tab)).is_none());
+
+        assert!(app.is_command_mode());
+        assert_eq!(app.command_text(), "noop ");
+        assert_eq!(input_text(&app), "");
+    }
+
+    #[test]
+    fn command_completion_enter_applies_and_executes_unambiguous_candidate() {
+        let mut app = App::new("agent".to_string());
+        enter_command_mode(&mut app);
+        type_keys(&mut app, "no");
+
+        let method = handle_key(&mut app, key(KeyCode::Enter));
+
+        assert!(method.is_none());
+        assert!(!app.is_command_mode());
+        assert_eq!(input_text(&app), "");
+        assert!(has_alert(&app, "noop: no action"));
+    }
+
+    #[test]
+    fn command_completion_ambiguous_candidate_requires_selection_or_more_input() {
+        let mut app = App::new("agent".to_string());
+        register_test_command(&mut app, "open", "open", parse_no_args, "open executed");
+        register_test_command(
+            &mut app,
+            "options",
+            "options",
+            parse_no_args,
+            "options executed",
+        );
+        enter_command_mode(&mut app);
+        type_keys(&mut app, "o");
+
+        assert!(handle_key(&mut app, key(KeyCode::Tab)).is_none());
+        assert_eq!(app.command_text(), "o");
+        assert!(app.is_command_mode());
+        assert!(has_alert(&app, "Ambiguous command completion"));
+
+        let before = app.blocks.len();
+        let method = handle_key(&mut app, key(KeyCode::Enter));
+        assert!(method.is_none());
+        assert_eq!(app.command_text(), "o");
+        assert!(app.is_command_mode());
+        assert!(app.blocks.len() > before);
+        assert!(!has_alert(&app, "open executed"));
+        assert!(!has_alert(&app, "options executed"));
+    }
+
+    #[test]
+    fn command_completion_selected_candidate_applies_on_enter() {
+        let mut app = App::new("agent".to_string());
+        register_test_command(&mut app, "open", "open", parse_no_args, "open executed");
+        register_test_command(
+            &mut app,
+            "options",
+            "options",
+            parse_no_args,
+            "options executed",
+        );
+        enter_command_mode(&mut app);
+        type_keys(&mut app, "o");
+
+        assert!(handle_key(&mut app, key(KeyCode::Down)).is_none());
+        let method = handle_key(&mut app, key(KeyCode::Enter));
+
+        assert!(method.is_none());
+        assert!(!app.is_command_mode());
+        assert!(has_alert(&app, "open executed"));
+        assert!(!has_alert(&app, "options executed"));
+    }
+
+    #[test]
+    fn command_completion_argument_required_keeps_command_mode_after_name_completion() {
+        let mut app = App::new("agent".to_string());
+        register_test_command(
+            &mut app,
+            "open",
+            "open <path>",
+            parse_required_arg,
+            "open executed",
+        );
+        enter_command_mode(&mut app);
+        type_keys(&mut app, "op");
+
+        let method = handle_key(&mut app, key(KeyCode::Enter));
+
+        assert!(method.is_none());
+        assert!(app.is_command_mode());
+        assert_eq!(app.command_text(), "open ");
+        assert!(has_alert(&app, "Invalid arguments. Usage: open <path>"));
+        assert!(!has_alert(&app, "open executed"));
+        assert_eq!(input_text(&app), "");
+    }
+
+    #[test]
+    fn command_completion_does_not_affect_normal_composer_without_popup() {
+        let mut app = App::new("agent".to_string());
+        type_keys(&mut app, "hello");
+
+        assert!(handle_key(&mut app, key(KeyCode::Tab)).is_none());
+
+        assert!(!app.is_command_mode());
+        assert_eq!(input_text(&app), "hello");
+    }
+
+    fn enter_command_mode(app: &mut App) {
+        assert!(handle_key(app, key(KeyCode::Char(':'))).is_none());
+        assert!(app.is_command_mode());
+    }
+
+    fn type_keys(app: &mut App, text: &str) {
+        for c in text.chars() {
+            assert!(handle_key(app, key(KeyCode::Char(c))).is_none());
+        }
+    }
+
+    fn key(code: KeyCode) -> KeyEvent {
+        KeyEvent::new(code, KeyModifiers::NONE)
+    }
+
+    fn has_alert(app: &App, needle: &str) -> bool {
+        app.blocks.iter().any(|block| match block {
+            crate::block::Block::Alert { message, .. } => message.contains(needle),
+            _ => false,
+        })
+    }
+
+    fn register_test_command(
+        app: &mut App,
+        name: &'static str,
+        usage: &'static str,
+        argument_parser: crate::command::ArgumentParser,
+        message: &'static str,
+    ) {
+        app.command_registry.register(crate::command::CommandSpec {
+            name,
+            aliases: &[],
+            usage,
+            description: "test command",
+            argument_parser,
+            can_execute: test_command_available,
+            executor: test_command_executor,
+        });
+        TEST_COMMAND_MESSAGES.with(|messages| messages.borrow_mut().push((name, message)));
+    }
+
+    thread_local! {
+        static TEST_COMMAND_MESSAGES: std::cell::RefCell<Vec<(&'static str, &'static str)>> =
+            const { std::cell::RefCell::new(Vec::new()) };
+    }
+
+    fn parse_no_args(
+        raw: &str,
+    ) -> Result<crate::command::CommandArgs, crate::command::CommandDiagnostic> {
+        Ok(crate::command::CommandArgs::parse_whitespace(raw))
+    }
+
+    fn parse_required_arg(
+        raw: &str,
+    ) -> Result<crate::command::CommandArgs, crate::command::CommandDiagnostic> {
+        let args = crate::command::CommandArgs::parse_whitespace(raw);
+        if args.argv().is_empty() {
+            return Err(crate::command::CommandDiagnostic::new(
+                "Invalid arguments. Usage: open <path>",
+            ));
+        }
+        Ok(args)
+    }
+
+    fn test_command_available(
+        _environment: &crate::command::CommandEnvironment,
+    ) -> Result<(), crate::command::CommandDiagnostic> {
+        Ok(())
+    }
+
+    fn test_command_executor(
+        invocation: crate::command::CommandInvocation<'_>,
+    ) -> crate::command::CommandExecution {
+        let message = TEST_COMMAND_MESSAGES
+            .with(|messages| {
+                messages
+                    .borrow()
+                    .iter()
+                    .find(|(name, _)| *name == invocation.command.name)
+                    .map(|(_, message)| *message)
+            })
+            .unwrap_or("test command executed");
+        crate::command::CommandExecution::notice(message)
+    }
+
     fn input_text(app: &App) -> String {
         protocol::Segment::flatten_to_text(&app.input.submit_segments())
     }
diff --git a/crates/tui/src/ui.rs b/crates/tui/src/ui.rs
index 5ef06cb9..5cf5ddd5 100644
--- a/crates/tui/src/ui.rs
+++ b/crates/tui/src/ui.rs
@@ -291,11 +291,29 @@ fn draw_command_popup(frame: &mut Frame, app: &App, input_area: Rect) {
         .add_modifier(Modifier::BOLD);
     let description_style = Style::default().fg(Color::DarkGray);
     let mut lines: Vec<Line<'static>> = Vec::with_capacity(popup_h as usize);
-    for candidate in visible_suggestions.iter().take(popup_h as usize) {
+    let selected = app.command_completion_selected();
+    for (idx, candidate) in visible_suggestions
+        .iter()
+        .take(popup_h as usize)
+        .enumerate()
+    {
+        let selected_style = if Some(idx) == selected {
+            Style::default()
+                .bg(Color::DarkGray)
+                .add_modifier(Modifier::BOLD)
+        } else {
+            Style::default()
+        };
         lines.push(Line::from(vec![
-            Span::styled(candidate.name.to_owned(), command_style),
-            Span::styled(" — ", description_style),
-            Span::styled(candidate.description.to_owned(), description_style),
+            Span::styled(
+                candidate.name.to_owned(),
+                command_style.patch(selected_style),
+            ),
+            Span::styled(" — ", description_style.patch(selected_style)),
+            Span::styled(
+                candidate.description.to_owned(),
+                description_style.patch(selected_style),
+            ),
         ]));
     }