Make the REPL resilient enough for real interactive workflows

The custom crossterm editor now supports prompt history, slash-command tab
completion, multiline editing, and Ctrl-C semantics that clear partial input
without always terminating the session. The live REPL loop now distinguishes
buffer cancellation from clean exit, persists session state on meaningful
boundaries, and renders tool activity in a more structured way for terminal
use.

Constraint: Keep the active REPL on the existing crossterm path without adding a line-editor dependency
Rejected: Swap to rustyline or reedline | broader integration risk than this polish pass justifies
Confidence: medium
Scope-risk: moderate
Reversibility: clean
Directive: Keep editor state logic generic in input.rs and leave REPL policy decisions in main.rs
Tested: cargo fmt --manifest-path rust/Cargo.toml --all; cargo clippy --manifest-path rust/Cargo.toml --all-targets --all-features -- -D warnings; cargo test --manifest-path rust/Cargo.toml
Not-tested: Interactive manual terminal smoke test for arrow keys/tab/Ctrl-C in a live TTY

rust/crates/rusty-claude-cli/src/app.rs

@@ -2,7 +2,7 @@ use std::io::{self, Write};
 use std::path::PathBuf;
 
 use crate::args::{OutputFormat, PermissionMode};
-use crate::input::LineEditor;
+use crate::input::{LineEditor, ReadOutcome};
 use crate::render::{Spinner, TerminalRenderer};
 use runtime::{ConversationClient, ConversationMessage, RuntimeError, StreamEvent, UsageSummary};
 
@@ -111,17 +111,22 @@ impl CliApp {
     }
 
     pub fn run_repl(&mut self) -> io::Result<()> {
-        let editor = LineEditor::new("› ");
+        let mut editor = LineEditor::new("› ", Vec::new());
         println!("Rusty Claude CLI interactive mode");
         println!("Type /help for commands. Shift+Enter or Ctrl+J inserts a newline.");
 
-        while let Some(input) = editor.read_line()? {
+        loop {
+            match editor.read_line()? {
+                ReadOutcome::Submit(input) => {
                     if input.trim().is_empty() {
                         continue;
                     }
-
                     self.handle_submission(&input, &mut io::stdout())?;
                 }
+                ReadOutcome::Cancel => continue,
+                ReadOutcome::Exit => break,
+            }
+        }
 
         Ok(())
     }

rust/crates/rusty-claude-cli/src/input.rs

@@ -1,9 +1,8 @@
 use std::io::{self, IsTerminal, Write};
 
-use crossterm::cursor::MoveToColumn;
+use crossterm::cursor::{MoveDown, MoveToColumn, MoveUp};
 use crossterm::event::{self, Event, KeyCode, KeyEvent, KeyModifiers};
 use crossterm::queue;
-use crossterm::style::Print;
 use crossterm::terminal::{disable_raw_mode, enable_raw_mode, Clear, ClearType};
 
 #[derive(Debug, Clone, PartialEq, Eq)]
@@ -85,21 +84,124 @@ impl InputBuffer {
         self.buffer.clear();
         self.cursor = 0;
     }
+
+    pub fn replace(&mut self, value: impl Into<String>) {
+        self.buffer = value.into();
+        self.cursor = self.buffer.len();
+    }
+
+    #[must_use]
+    fn current_command_prefix(&self) -> Option<&str> {
+        if self.cursor != self.buffer.len() {
+            return None;
+        }
+        let prefix = &self.buffer[..self.cursor];
+        if prefix.contains(char::is_whitespace) || !prefix.starts_with('/') {
+            return None;
+        }
+        Some(prefix)
+    }
+
+    pub fn complete_slash_command(&mut self, candidates: &[String]) -> bool {
+        let Some(prefix) = self.current_command_prefix() else {
+            return false;
+        };
+
+        let matches = candidates
+            .iter()
+            .filter(|candidate| candidate.starts_with(prefix))
+            .map(String::as_str)
+            .collect::<Vec<_>>();
+        if matches.is_empty() {
+            return false;
+        }
+
+        let replacement = longest_common_prefix(&matches);
+        if replacement == prefix {
+            return false;
+        }
+
+        self.replace(replacement);
+        true
+    }
+}
+
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct RenderedBuffer {
+    lines: Vec<String>,
+    cursor_row: u16,
+    cursor_col: u16,
+}
+
+impl RenderedBuffer {
+    #[must_use]
+    pub fn line_count(&self) -> usize {
+        self.lines.len()
+    }
+
+    fn write(&self, out: &mut impl Write) -> io::Result<()> {
+        for (index, line) in self.lines.iter().enumerate() {
+            if index > 0 {
+                writeln!(out)?;
+            }
+            write!(out, "{line}")?;
+        }
+        Ok(())
+    }
+
+    #[cfg(test)]
+    #[must_use]
+    pub fn lines(&self) -> &[String] {
+        &self.lines
+    }
+
+    #[cfg(test)]
+    #[must_use]
+    pub fn cursor_position(&self) -> (u16, u16) {
+        (self.cursor_row, self.cursor_col)
+    }
+}
+
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub enum ReadOutcome {
+    Submit(String),
+    Cancel,
+    Exit,
 }
 
 pub struct LineEditor {
     prompt: String,
+    continuation_prompt: String,
+    history: Vec<String>,
+    history_index: Option<usize>,
+    draft: Option<String>,
+    completions: Vec<String>,
 }
 
 impl LineEditor {
     #[must_use]
-    pub fn new(prompt: impl Into<String>) -> Self {
+    pub fn new(prompt: impl Into<String>, completions: Vec<String>) -> Self {
         Self {
             prompt: prompt.into(),
+            continuation_prompt: String::from("> "),
+            history: Vec::new(),
+            history_index: None,
+            draft: None,
+            completions,
         }
     }
 
-    pub fn read_line(&self) -> io::Result<Option<String>> {
+    pub fn push_history(&mut self, entry: impl Into<String>) {
+        let entry = entry.into();
+        if entry.trim().is_empty() {
+            return;
+        }
+        self.history.push(entry);
+        self.history_index = None;
+        self.draft = None;
+    }
+
+    pub fn read_line(&mut self) -> io::Result<ReadOutcome> {
         if !io::stdin().is_terminal() || !io::stdout().is_terminal() {
             return self.read_line_fallback();
         }
@@ -107,29 +209,43 @@ impl LineEditor {
         enable_raw_mode()?;
         let mut stdout = io::stdout();
         let mut input = InputBuffer::new();
-        self.redraw(&mut stdout, &input)?;
+        let mut rendered_lines = 1usize;
+        self.redraw(&mut stdout, &input, rendered_lines)?;
 
         loop {
             let event = event::read()?;
             if let Event::Key(key) = event {
-                match Self::handle_key(key, &mut input) {
-                    EditorAction::Continue => self.redraw(&mut stdout, &input)?,
+                match self.handle_key(key, &mut input) {
+                    EditorAction::Continue => {
+                        rendered_lines = self.redraw(&mut stdout, &input, rendered_lines)?;
+                    }
                     EditorAction::Submit => {
                         disable_raw_mode()?;
                         writeln!(stdout)?;
-                        return Ok(Some(input.as_str().to_owned()));
+                        self.history_index = None;
+                        self.draft = None;
+                        return Ok(ReadOutcome::Submit(input.as_str().to_owned()));
                     }
                     EditorAction::Cancel => {
                         disable_raw_mode()?;
                         writeln!(stdout)?;
-                        return Ok(None);
+                        self.history_index = None;
+                        self.draft = None;
+                        return Ok(ReadOutcome::Cancel);
+                    }
+                    EditorAction::Exit => {
+                        disable_raw_mode()?;
+                        writeln!(stdout)?;
+                        self.history_index = None;
+                        self.draft = None;
+                        return Ok(ReadOutcome::Exit);
                     }
                 }
             }
         }
     }
 
-    fn read_line_fallback(&self) -> io::Result<Option<String>> {
+    fn read_line_fallback(&self) -> io::Result<ReadOutcome> {
         let mut stdout = io::stdout();
         write!(stdout, "{}", self.prompt)?;
         stdout.flush()?;
@@ -137,22 +253,32 @@ impl LineEditor {
         let mut buffer = String::new();
         let bytes_read = io::stdin().read_line(&mut buffer)?;
         if bytes_read == 0 {
-            return Ok(None);
+            return Ok(ReadOutcome::Exit);
         }
 
         while matches!(buffer.chars().last(), Some('\n' | '\r')) {
             buffer.pop();
         }
-        Ok(Some(buffer))
+        Ok(ReadOutcome::Submit(buffer))
     }
 
-    fn handle_key(key: KeyEvent, input: &mut InputBuffer) -> EditorAction {
+    #[allow(clippy::too_many_lines)]
+    fn handle_key(&mut self, key: KeyEvent, input: &mut InputBuffer) -> EditorAction {
         match key {
             KeyEvent {
                 code: KeyCode::Char('c'),
                 modifiers,
                 ..
-            } if modifiers.contains(KeyModifiers::CONTROL) => EditorAction::Cancel,
+            } if modifiers.contains(KeyModifiers::CONTROL) => {
+                if input.as_str().is_empty() {
+                    EditorAction::Exit
+                } else {
+                    input.clear();
+                    self.history_index = None;
+                    self.draft = None;
+                    EditorAction::Cancel
+                }
+            }
             KeyEvent {
                 code: KeyCode::Char('j'),
                 modifiers,
@@ -194,6 +320,25 @@ impl LineEditor {
                 input.move_right();
                 EditorAction::Continue
             }
+            KeyEvent {
+                code: KeyCode::Up, ..
+            } => {
+                self.navigate_history_up(input);
+                EditorAction::Continue
+            }
+            KeyEvent {
+                code: KeyCode::Down,
+                ..
+            } => {
+                self.navigate_history_down(input);
+                EditorAction::Continue
+            }
+            KeyEvent {
+                code: KeyCode::Tab, ..
+            } => {
+                input.complete_slash_command(&self.completions);
+                EditorAction::Continue
+            }
             KeyEvent {
                 code: KeyCode::Home,
                 ..
@@ -211,6 +356,8 @@ impl LineEditor {
                 code: KeyCode::Esc, ..
             } => {
                 input.clear();
+                self.history_index = None;
+                self.draft = None;
                 EditorAction::Cancel
             }
             KeyEvent {
@@ -219,22 +366,74 @@ impl LineEditor {
                 ..
             } if modifiers.is_empty() || modifiers == KeyModifiers::SHIFT => {
                 input.insert(ch);
+                self.history_index = None;
+                self.draft = None;
                 EditorAction::Continue
             }
             _ => EditorAction::Continue,
         }
     }
 
-    fn redraw(&self, out: &mut impl Write, input: &InputBuffer) -> io::Result<()> {
-        let display = input.as_str().replace('\n', "\\n\n> ");
+    fn navigate_history_up(&mut self, input: &mut InputBuffer) {
+        if self.history.is_empty() {
+            return;
+        }
+
+        match self.history_index {
+            Some(0) => {}
+            Some(index) => {
+                let next_index = index - 1;
+                input.replace(self.history[next_index].clone());
+                self.history_index = Some(next_index);
+            }
+            None => {
+                self.draft = Some(input.as_str().to_owned());
+                let next_index = self.history.len() - 1;
+                input.replace(self.history[next_index].clone());
+                self.history_index = Some(next_index);
+            }
+        }
+    }
+
+    fn navigate_history_down(&mut self, input: &mut InputBuffer) {
+        let Some(index) = self.history_index else {
+            return;
+        };
+
+        if index + 1 < self.history.len() {
+            let next_index = index + 1;
+            input.replace(self.history[next_index].clone());
+            self.history_index = Some(next_index);
+            return;
+        }
+
+        input.replace(self.draft.take().unwrap_or_default());
+        self.history_index = None;
+    }
+
+    fn redraw(
+        &self,
+        out: &mut impl Write,
+        input: &InputBuffer,
+        previous_line_count: usize,
+    ) -> io::Result<usize> {
+        let rendered = render_buffer(&self.prompt, &self.continuation_prompt, input);
+        if previous_line_count > 1 {
+            queue!(out, MoveUp(saturating_u16(previous_line_count - 1)))?;
+        }
+        queue!(out, MoveToColumn(0), Clear(ClearType::FromCursorDown),)?;
+        rendered.write(out)?;
         queue!(
             out,
+            MoveUp(saturating_u16(rendered.line_count().saturating_sub(1))),
             MoveToColumn(0),
-            Clear(ClearType::CurrentLine),
-            Print(&self.prompt),
-            Print(display),
         )?;
-        out.flush()
+        if rendered.cursor_row > 0 {
+            queue!(out, MoveDown(rendered.cursor_row))?;
+        }
+        queue!(out, MoveToColumn(rendered.cursor_col))?;
+        out.flush()?;
+        Ok(rendered.line_count())
     }
 }
 
@@ -243,11 +442,76 @@ enum EditorAction {
     Continue,
     Submit,
     Cancel,
+    Exit,
+}
+
+#[must_use]
+pub fn render_buffer(
+    prompt: &str,
+    continuation_prompt: &str,
+    input: &InputBuffer,
+) -> RenderedBuffer {
+    let before_cursor = &input.as_str()[..input.cursor];
+    let cursor_row = saturating_u16(before_cursor.chars().filter(|ch| *ch == '\n').count());
+    let cursor_line = before_cursor.rsplit('\n').next().unwrap_or_default();
+    let cursor_prompt = if cursor_row == 0 {
+        prompt
+    } else {
+        continuation_prompt
+    };
+    let cursor_col = saturating_u16(cursor_prompt.chars().count() + cursor_line.chars().count());
+
+    let mut lines = Vec::new();
+    for (index, line) in input.as_str().split('\n').enumerate() {
+        let prefix = if index == 0 {
+            prompt
+        } else {
+            continuation_prompt
+        };
+        lines.push(format!("{prefix}{line}"));
+    }
+    if lines.is_empty() {
+        lines.push(prompt.to_string());
+    }
+
+    RenderedBuffer {
+        lines,
+        cursor_row,
+        cursor_col,
+    }
+}
+
+#[must_use]
+fn longest_common_prefix(values: &[&str]) -> String {
+    let Some(first) = values.first() else {
+        return String::new();
+    };
+
+    let mut prefix = (*first).to_string();
+    for value in values.iter().skip(1) {
+        while !value.starts_with(&prefix) {
+            prefix.pop();
+            if prefix.is_empty() {
+                break;
+            }
+        }
+    }
+    prefix
+}
+
+#[must_use]
+fn saturating_u16(value: usize) -> u16 {
+    u16::try_from(value).unwrap_or(u16::MAX)
 }
 
 #[cfg(test)]
 mod tests {
-    use super::InputBuffer;
+    use super::{render_buffer, InputBuffer, LineEditor};
+    use crossterm::event::{KeyCode, KeyEvent, KeyModifiers};
+
+    fn key(code: KeyCode) -> KeyEvent {
+        KeyEvent::new(code, KeyModifiers::NONE)
+    }
 
     #[test]
     fn supports_basic_line_editing() {
@@ -266,4 +530,119 @@ mod tests {
         assert_eq!(input.as_str(), "hix");
         assert_eq!(input.cursor(), 2);
     }
+
+    #[test]
+    fn completes_unique_slash_command() {
+        let mut input = InputBuffer::new();
+        for ch in "/he".chars() {
+            input.insert(ch);
+        }
+
+        assert!(input.complete_slash_command(&[
+            "/help".to_string(),
+            "/hello".to_string(),
+            "/status".to_string(),
+        ]));
+        assert_eq!(input.as_str(), "/hel");
+
+        assert!(input.complete_slash_command(&["/help".to_string(), "/status".to_string()]));
+        assert_eq!(input.as_str(), "/help");
+    }
+
+    #[test]
+    fn ignores_completion_when_prefix_is_not_a_slash_command() {
+        let mut input = InputBuffer::new();
+        for ch in "hello".chars() {
+            input.insert(ch);
+        }
+
+        assert!(!input.complete_slash_command(&["/help".to_string()]));
+        assert_eq!(input.as_str(), "hello");
+    }
+
+    #[test]
+    fn history_navigation_restores_current_draft() {
+        let mut editor = LineEditor::new("› ", vec![]);
+        editor.push_history("/help");
+        editor.push_history("status report");
+
+        let mut input = InputBuffer::new();
+        for ch in "draft".chars() {
+            input.insert(ch);
+        }
+
+        let _ = editor.handle_key(key(KeyCode::Up), &mut input);
+        assert_eq!(input.as_str(), "status report");
+
+        let _ = editor.handle_key(key(KeyCode::Up), &mut input);
+        assert_eq!(input.as_str(), "/help");
+
+        let _ = editor.handle_key(key(KeyCode::Down), &mut input);
+        assert_eq!(input.as_str(), "status report");
+
+        let _ = editor.handle_key(key(KeyCode::Down), &mut input);
+        assert_eq!(input.as_str(), "draft");
+    }
+
+    #[test]
+    fn tab_key_completes_from_editor_candidates() {
+        let mut editor = LineEditor::new(
+            "› ",
+            vec![
+                "/help".to_string(),
+                "/status".to_string(),
+                "/session".to_string(),
+            ],
+        );
+        let mut input = InputBuffer::new();
+        for ch in "/st".chars() {
+            input.insert(ch);
+        }
+
+        let _ = editor.handle_key(key(KeyCode::Tab), &mut input);
+        assert_eq!(input.as_str(), "/status");
+    }
+
+    #[test]
+    fn renders_multiline_buffers_with_continuation_prompt() {
+        let mut input = InputBuffer::new();
+        for ch in "hello\nworld".chars() {
+            if ch == '\n' {
+                input.insert_newline();
+            } else {
+                input.insert(ch);
+            }
+        }
+
+        let rendered = render_buffer("› ", "> ", &input);
+        assert_eq!(
+            rendered.lines(),
+            &["› hello".to_string(), "> world".to_string()]
+        );
+        assert_eq!(rendered.cursor_position(), (1, 7));
+    }
+
+    #[test]
+    fn ctrl_c_exits_only_when_buffer_is_empty() {
+        let mut editor = LineEditor::new("› ", vec![]);
+        let mut empty = InputBuffer::new();
+        assert!(matches!(
+            editor.handle_key(
+                KeyEvent::new(KeyCode::Char('c'), KeyModifiers::CONTROL),
+                &mut empty,
+            ),
+            super::EditorAction::Exit
+        ));
+
+        let mut filled = InputBuffer::new();
+        filled.insert('x');
+        assert!(matches!(
+            editor.handle_key(
+                KeyEvent::new(KeyCode::Char('c'), KeyModifiers::CONTROL),
+                &mut filled,
+            ),
+            super::EditorAction::Cancel
+        ));
+        assert!(filled.as_str().is_empty());
+    }
 }

rust/crates/rusty-claude-cli/src/main.rs

@@ -14,7 +14,9 @@ use api::{
     ToolResultContentBlock,
 };
 
-use commands::{render_slash_command_help, resume_supported_slash_commands, SlashCommand};
+use commands::{
+    render_slash_command_help, resume_supported_slash_commands, slash_command_specs, SlashCommand,
+};
 use compat_harness::{extract_manifest, UpstreamPaths};
 use render::{Spinner, TerminalRenderer};
 use runtime::{
@@ -716,22 +718,35 @@ fn run_repl(
     allowed_tools: Option<AllowedToolSet>,
 ) -> Result<(), Box<dyn std::error::Error>> {
     let mut cli = LiveCli::new(model, true, allowed_tools)?;
-    let editor = input::LineEditor::new("› ");
+    let mut editor = input::LineEditor::new("› ", slash_command_completion_candidates());
     println!("{}", cli.startup_banner());
 
-    while let Some(input) = editor.read_line()? {
-        let trimmed = input.trim();
+    loop {
+        match editor.read_line()? {
+            input::ReadOutcome::Submit(input) => {
+                let trimmed = input.trim().to_string();
                 if trimmed.is_empty() {
                     continue;
                 }
-        if matches!(trimmed, "/exit" | "/quit") {
+                if matches!(trimmed.as_str(), "/exit" | "/quit") {
+                    cli.persist_session()?;
                     break;
                 }
-        if let Some(command) = SlashCommand::parse(trimmed) {
-            cli.handle_repl_command(command)?;
+                if let Some(command) = SlashCommand::parse(&trimmed) {
+                    if cli.handle_repl_command(command)? {
+                        cli.persist_session()?;
+                    }
                     continue;
                 }
-        cli.run_turn(trimmed)?;
+                editor.push_history(input);
+                cli.run_turn(&trimmed)?;
+            }
+            input::ReadOutcome::Cancel => {}
+            input::ReadOutcome::Exit => {
+                cli.persist_session()?;
+                break;
+            }
+        }
     }
 
     Ok(())
@@ -885,28 +900,60 @@ impl LiveCli {
     fn handle_repl_command(
         &mut self,
         command: SlashCommand,
-    ) -> Result<(), Box<dyn std::error::Error>> {
-        match command {
-            SlashCommand::Help => println!("{}", render_repl_help()),
-            SlashCommand::Status => self.print_status(),
-            SlashCommand::Compact => self.compact()?,
+    ) -> Result<bool, Box<dyn std::error::Error>> {
+        Ok(match command {
+            SlashCommand::Help => {
+                println!("{}", render_repl_help());
+                false
+            }
+            SlashCommand::Status => {
+                self.print_status();
+                false
+            }
+            SlashCommand::Compact => {
+                self.compact()?;
+                false
+            }
             SlashCommand::Model { model } => self.set_model(model)?,
             SlashCommand::Permissions { mode } => self.set_permissions(mode)?,
             SlashCommand::Clear { confirm } => self.clear_session(confirm)?,
-            SlashCommand::Cost => self.print_cost(),
+            SlashCommand::Cost => {
+                self.print_cost();
+                false
+            }
             SlashCommand::Resume { session_path } => self.resume_session(session_path)?,
-            SlashCommand::Config { section } => Self::print_config(section.as_deref())?,
-            SlashCommand::Memory => Self::print_memory()?,
-            SlashCommand::Init => Self::run_init()?,
-            SlashCommand::Diff => Self::print_diff()?,
-            SlashCommand::Version => Self::print_version(),
-            SlashCommand::Export { path } => self.export_session(path.as_deref())?,
+            SlashCommand::Config { section } => {
+                Self::print_config(section.as_deref())?;
+                false
+            }
+            SlashCommand::Memory => {
+                Self::print_memory()?;
+                false
+            }
+            SlashCommand::Init => {
+                Self::run_init()?;
+                false
+            }
+            SlashCommand::Diff => {
+                Self::print_diff()?;
+                false
+            }
+            SlashCommand::Version => {
+                Self::print_version();
+                false
+            }
+            SlashCommand::Export { path } => {
+                self.export_session(path.as_deref())?;
+                false
+            }
             SlashCommand::Session { action, target } => {
-                self.handle_session_command(action.as_deref(), target.as_deref())?;
+                self.handle_session_command(action.as_deref(), target.as_deref())?
             }
-            SlashCommand::Unknown(name) => eprintln!("unknown slash command: /{name}"),
+            SlashCommand::Unknown(name) => {
+                eprintln!("unknown slash command: /{name}");
+                false
             }
-        Ok(())
+        })
     }
 
     fn persist_session(&self) -> Result<(), Box<dyn std::error::Error>> {
@@ -934,7 +981,7 @@ impl LiveCli {
         );
     }
 
-    fn set_model(&mut self, model: Option<String>) -> Result<(), Box<dyn std::error::Error>> {
+    fn set_model(&mut self, model: Option<String>) -> Result<bool, Box<dyn std::error::Error>> {
         let Some(model) = model else {
             println!(
                 "{}",
@@ -944,7 +991,7 @@ impl LiveCli {
                     self.runtime.usage().turns(),
                 )
             );
-            return Ok(());
+            return Ok(false);
         };
 
         if model == self.model {
@@ -956,7 +1003,7 @@ impl LiveCli {
                     self.runtime.usage().turns(),
                 )
             );
-            return Ok(());
+            return Ok(false);
         }
 
         let previous = self.model.clone();
@@ -970,18 +1017,20 @@ impl LiveCli {
             self.allowed_tools.clone(),
         )?;
         self.model.clone_from(&model);
-        self.persist_session()?;
         println!(
             "{}",
             format_model_switch_report(&previous, &model, message_count)
         );
-        Ok(())
+        Ok(true)
     }
 
-    fn set_permissions(&mut self, mode: Option<String>) -> Result<(), Box<dyn std::error::Error>> {
+    fn set_permissions(
+        &mut self,
+        mode: Option<String>,
+    ) -> Result<bool, Box<dyn std::error::Error>> {
         let Some(mode) = mode else {
             println!("{}", format_permissions_report(permission_mode_label()));
-            return Ok(());
+            return Ok(false);
         };
 
         let normalized = normalize_permission_mode(&mode).ok_or_else(|| {
@@ -992,7 +1041,7 @@ impl LiveCli {
 
         if normalized == permission_mode_label() {
             println!("{}", format_permissions_report(normalized));
-            return Ok(());
+            return Ok(false);
         }
 
         let previous = permission_mode_label().to_string();
@@ -1005,20 +1054,19 @@ impl LiveCli {
             self.allowed_tools.clone(),
             normalized,
         )?;
-        self.persist_session()?;
         println!(
             "{}",
             format_permissions_switch_report(&previous, normalized)
         );
-        Ok(())
+        Ok(true)
     }
 
-    fn clear_session(&mut self, confirm: bool) -> Result<(), Box<dyn std::error::Error>> {
+    fn clear_session(&mut self, confirm: bool) -> Result<bool, Box<dyn std::error::Error>> {
         if !confirm {
             println!(
                 "clear: confirmation required; run /clear --confirm to start a fresh session."
             );
-            return Ok(());
+            return Ok(false);
         }
 
         self.session = create_managed_session_handle()?;
@@ -1030,14 +1078,13 @@ impl LiveCli {
             self.allowed_tools.clone(),
             permission_mode_label(),
         )?;
-        self.persist_session()?;
         println!(
             "Session cleared\n  Mode             fresh session\n  Preserved model  {}\n  Permission mode  {}\n  Session          {}",
             self.model,
             permission_mode_label(),
             self.session.id,
         );
-        Ok(())
+        Ok(true)
     }
 
     fn print_cost(&self) {
@@ -1048,10 +1095,10 @@ impl LiveCli {
     fn resume_session(
         &mut self,
         session_path: Option<String>,
-    ) -> Result<(), Box<dyn std::error::Error>> {
+    ) -> Result<bool, Box<dyn std::error::Error>> {
         let Some(session_ref) = session_path else {
             println!("Usage: /resume <session-path>");
-            return Ok(());
+            return Ok(false);
         };
 
         let handle = resolve_session_reference(&session_ref)?;
@@ -1066,7 +1113,6 @@ impl LiveCli {
             permission_mode_label(),
         )?;
         self.session = handle;
-        self.persist_session()?;
         println!(
             "{}",
             format_resume_report(
@@ -1075,7 +1121,7 @@ impl LiveCli {
                 self.runtime.usage().turns(),
             )
         );
-        Ok(())
+        Ok(true)
     }
 
     fn print_config(section: Option<&str>) -> Result<(), Box<dyn std::error::Error>> {
@@ -1120,16 +1166,16 @@ impl LiveCli {
         &mut self,
         action: Option<&str>,
         target: Option<&str>,
-    ) -> Result<(), Box<dyn std::error::Error>> {
+    ) -> Result<bool, Box<dyn std::error::Error>> {
         match action {
             None | Some("list") => {
                 println!("{}", render_session_list(&self.session.id)?);
-                Ok(())
+                Ok(false)
             }
             Some("switch") => {
                 let Some(target) = target else {
                     println!("Usage: /session switch <session-id>");
-                    return Ok(());
+                    return Ok(false);
                 };
                 let handle = resolve_session_reference(target)?;
                 let session = Session::load_from_path(&handle.path)?;
@@ -1143,18 +1189,17 @@ impl LiveCli {
                     permission_mode_label(),
                 )?;
                 self.session = handle;
-                self.persist_session()?;
                 println!(
                     "Session switched\n  Active session   {}\n  File             {}\n  Messages         {}",
                     self.session.id,
                     self.session.path.display(),
                     message_count,
                 );
-                Ok(())
+                Ok(true)
             }
             Some(other) => {
                 println!("Unknown /session action '{other}'. Use /session list or /session switch <session-id>.");
-                Ok(())
+                Ok(false)
             }
         }
     }
@@ -1283,6 +1328,10 @@ fn render_repl_help() -> String {
         "REPL".to_string(),
         "  /exit                Quit the REPL".to_string(),
         "  /quit                Quit the REPL".to_string(),
+        "  Up/Down              Navigate prompt history".to_string(),
+        "  Tab                  Complete slash commands".to_string(),
+        "  Ctrl-C               Clear input (or exit on empty prompt)".to_string(),
+        "  Shift+Enter/Ctrl+J   Insert a newline".to_string(),
         String::new(),
         render_slash_command_help(),
     ]
@@ -1866,6 +1915,63 @@ impl ApiClient for AnthropicRuntimeClient {
     }
 }
 
+fn slash_command_completion_candidates() -> Vec<String> {
+    slash_command_specs()
+        .iter()
+        .map(|spec| format!("/{}", spec.name))
+        .collect()
+}
+
+fn format_tool_call_start(name: &str, input: &str) -> String {
+    format!(
+        "Tool call
+  Name             {name}
+  Input            {}",
+        summarize_tool_payload(input)
+    )
+}
+
+fn format_tool_result(name: &str, output: &str, is_error: bool) -> String {
+    let status = if is_error { "error" } else { "ok" };
+    format!(
+        "### Tool `{name}`
+
+- Status: {status}
+- Output:
+
+```json
+{}
+```
+",
+        prettify_tool_payload(output)
+    )
+}
+
+fn summarize_tool_payload(payload: &str) -> String {
+    let compact = match serde_json::from_str::<serde_json::Value>(payload) {
+        Ok(value) => value.to_string(),
+        Err(_) => payload.trim().to_string(),
+    };
+    truncate_for_summary(&compact, 96)
+}
+
+fn prettify_tool_payload(payload: &str) -> String {
+    match serde_json::from_str::<serde_json::Value>(payload) {
+        Ok(value) => serde_json::to_string_pretty(&value).unwrap_or_else(|_| payload.to_string()),
+        Err(_) => payload.to_string(),
+    }
+}
+
+fn truncate_for_summary(value: &str, limit: usize) -> String {
+    let mut chars = value.chars();
+    let truncated = chars.by_ref().take(limit).collect::<String>();
+    if chars.next().is_some() {
+        format!("{truncated}…")
+    } else {
+        truncated
+    }
+}
+
 fn push_output_block(
     block: OutputContentBlock,
     out: &mut impl Write,
@@ -1882,6 +1988,14 @@ fn push_output_block(
             }
         }
         OutputContentBlock::ToolUse { id, name, input } => {
+            writeln!(
+                out,
+                "
+{}",
+                format_tool_call_start(&name, &input.to_string())
+            )
+            .and_then(|()| out.flush())
+            .map_err(|error| RuntimeError::new(error.to_string()))?;
             *pending_tool = Some((id, name, input.to_string()));
         }
     }
@@ -1941,13 +2055,19 @@ impl ToolExecutor for CliToolExecutor {
             .map_err(|error| ToolError::new(format!("invalid tool input JSON: {error}")))?;
         match execute_tool(tool_name, &value) {
             Ok(output) => {
-                let markdown = format!("### Tool `{tool_name}`\n\n```json\n{output}\n```\n");
+                let markdown = format_tool_result(tool_name, &output, false);
                 self.renderer
                     .stream_markdown(&markdown, &mut io::stdout())
                     .map_err(|error| ToolError::new(error.to_string()))?;
                 Ok(output)
             }
-            Err(error) => Err(ToolError::new(error)),
+            Err(error) => {
+                let markdown = format_tool_result(tool_name, &error, true);
+                self.renderer
+                    .stream_markdown(&markdown, &mut io::stdout())
+                    .map_err(|stream_error| ToolError::new(stream_error.to_string()))?;
+                Err(ToolError::new(error))
+            }
         }
     }
 }
@@ -2051,10 +2171,10 @@ mod tests {
         filter_tool_specs, format_compact_report, format_cost_report, format_init_report,
         format_model_report, format_model_switch_report, format_permissions_report,
         format_permissions_switch_report, format_resume_report, format_status_report,
-        normalize_permission_mode, parse_args, parse_git_status_metadata, render_config_report,
-        render_init_claude_md, render_memory_report, render_repl_help,
-        resume_supported_slash_commands, status_context, CliAction, CliOutputFormat, SlashCommand,
-        StatusUsage, DEFAULT_MODEL,
+        format_tool_call_start, format_tool_result, normalize_permission_mode, parse_args,
+        parse_git_status_metadata, render_config_report, render_init_claude_md,
+        render_memory_report, render_repl_help, resume_supported_slash_commands, status_context,
+        CliAction, CliOutputFormat, SlashCommand, StatusUsage, DEFAULT_MODEL,
     };
     use runtime::{ContentBlock, ConversationMessage, MessageRole};
     use std::path::{Path, PathBuf};
@@ -2516,4 +2636,22 @@ mod tests {
         assert_eq!(converted[1].role, "assistant");
         assert_eq!(converted[2].role, "user");
     }
+    #[test]
+    fn repl_help_mentions_history_completion_and_multiline() {
+        let help = render_repl_help();
+        assert!(help.contains("Up/Down"));
+        assert!(help.contains("Tab"));
+        assert!(help.contains("Shift+Enter/Ctrl+J"));
+    }
+
+    #[test]
+    fn tool_rendering_helpers_compact_output() {
+        let start = format_tool_call_start("read_file", r#"{"path":"src/main.rs"}"#);
+        assert!(start.contains("Tool call"));
+        assert!(start.contains("src/main.rs"));
+
+        let done = format_tool_result("read_file", r#"{"contents":"hello"}"#, false);
+        assert!(done.contains("Tool `read_file`"));
+        assert!(done.contains("contents"));
+    }
 }