diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 13da6f8..601cd38 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -3,6 +3,7 @@ name: CI
 on:
   push:
     branches: ["main", "master"]
+    tags: ["v*"]
   pull_request:
 
 jobs:
@@ -23,3 +24,36 @@ jobs:
 
       - name: Test
         run: cargo test --workspace --verbose
+
+  build-windows-client:
+    runs-on: ubuntu-latest
+    if: github.event_name == 'push'
+
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Install Rust (stable) + Windows target
+        uses: dtolnay/rust-toolchain@stable
+        with:
+          targets: x86_64-pc-windows-gnu
+
+      - name: Install MinGW cross-compiler
+        run: sudo apt-get update && sudo apt-get install -y gcc-mingw-w64-x86-64
+
+      - name: Cache dependencies
+        uses: Swatinem/rust-cache@v2
+        with:
+          key: windows-gnu
+
+      - name: Build Windows client (cross-compile)
+        run: |
+          cargo build --release --package helios-client --target x86_64-pc-windows-gnu
+        env:
+          CARGO_TARGET_X86_64_PC_WINDOWS_GNU_LINKER: x86_64-w64-mingw32-gcc
+
+      - name: Upload Windows client artifact
+        uses: actions/upload-artifact@v4
+        with:
+          name: helios-remote-client-windows
+          path: target/x86_64-pc-windows-gnu/release/helios-client.exe
+          if-no-files-found: error
diff --git a/crates/client/Cargo.toml b/crates/client/Cargo.toml
index c1b8ecb..6b81376 100644
--- a/crates/client/Cargo.toml
+++ b/crates/client/Cargo.toml
@@ -3,8 +3,27 @@ name = "helios-client"
 version = "0.1.0"
 edition = "2021"
 
-# Phase 2 — Windows client (not yet implemented)
-# See README.md in this crate for the planned implementation.
+[[bin]]
+name = "helios-client"
+path = "src/main.rs"
 
 [dependencies]
+tokio = { version = "1", features = ["full"] }
+tokio-tungstenite = { version = "0.21", features = ["connect"] }
+serde = { version = "1", features = ["derive"] }
+serde_json = "1"
 helios-common = { path = "../common" }
+dirs = "5"
+tracing = "0.1"
+tracing-subscriber = { version = "0.3", features = ["env-filter"] }
+base64 = "0.22"
+png = "0.17"
+futures-util = "0.3"
+
+[target.'cfg(windows)'.dependencies]
+windows = { version = "0.54", features = [
+    "Win32_Foundation",
+    "Win32_Graphics_Gdi",
+    "Win32_UI_Input_KeyboardAndMouse",
+    "Win32_System_Threading",
+] }
diff --git a/crates/client/src/input.rs b/crates/client/src/input.rs
new file mode 100644
index 0000000..152869d
--- /dev/null
+++ b/crates/client/src/input.rs
@@ -0,0 +1,154 @@
+/// Mouse click and keyboard input via Windows SendInput (or stub on non-Windows).
+use helios_common::MouseButton;
+
+#[cfg(windows)]
+pub fn click(x: i32, y: i32, button: &MouseButton) -> Result<(), String> {
+    use windows::Win32::UI::Input::KeyboardAndMouse::{
+        SendInput, INPUT, INPUT_MOUSE, MOUSEEVENTF_ABSOLUTE, MOUSEEVENTF_LEFTDOWN,
+        MOUSEEVENTF_LEFTUP, MOUSEEVENTF_MIDDLEDOWN, MOUSEEVENTF_MIDDLEUP, MOUSEEVENTF_MOVE,
+        MOUSEEVENTF_RIGHTDOWN, MOUSEEVENTF_RIGHTUP, MOUSEINPUT,
+    };
+    use windows::Win32::UI::WindowsAndMessaging::{GetSystemMetrics, SM_CXSCREEN, SM_CYSCREEN};
+
+    unsafe {
+        let screen_w = GetSystemMetrics(SM_CXSCREEN) as i32;
+        let screen_h = GetSystemMetrics(SM_CYSCREEN) as i32;
+
+        if screen_w == 0 || screen_h == 0 {
+            return Err(format!(
+                "Could not get screen dimensions: {screen_w}x{screen_h}"
+            ));
+        }
+
+        // Convert pixel coords to absolute 0-65535 range
+        let abs_x = ((x * 65535) / screen_w) as i32;
+        let abs_y = ((y * 65535) / screen_h) as i32;
+
+        let (down_flag, up_flag) = match button {
+            MouseButton::Left => (MOUSEEVENTF_LEFTDOWN, MOUSEEVENTF_LEFTUP),
+            MouseButton::Right => (MOUSEEVENTF_RIGHTDOWN, MOUSEEVENTF_RIGHTUP),
+            MouseButton::Middle => (MOUSEEVENTF_MIDDLEDOWN, MOUSEEVENTF_MIDDLEUP),
+        };
+
+        // Move to position
+        let move_input = INPUT {
+            r#type: INPUT_MOUSE,
+            Anonymous: windows::Win32::UI::Input::KeyboardAndMouse::INPUT_0 {
+                mi: MOUSEINPUT {
+                    dx: abs_x,
+                    dy: abs_y,
+                    mouseData: 0,
+                    dwFlags: MOUSEEVENTF_MOVE | MOUSEEVENTF_ABSOLUTE,
+                    time: 0,
+                    dwExtraInfo: 0,
+                },
+            },
+        };
+
+        let down_input = INPUT {
+            r#type: INPUT_MOUSE,
+            Anonymous: windows::Win32::UI::Input::KeyboardAndMouse::INPUT_0 {
+                mi: MOUSEINPUT {
+                    dx: abs_x,
+                    dy: abs_y,
+                    mouseData: 0,
+                    dwFlags: down_flag | MOUSEEVENTF_ABSOLUTE,
+                    time: 0,
+                    dwExtraInfo: 0,
+                },
+            },
+        };
+
+        let up_input = INPUT {
+            r#type: INPUT_MOUSE,
+            Anonymous: windows::Win32::UI::Input::KeyboardAndMouse::INPUT_0 {
+                mi: MOUSEINPUT {
+                    dx: abs_x,
+                    dy: abs_y,
+                    mouseData: 0,
+                    dwFlags: up_flag | MOUSEEVENTF_ABSOLUTE,
+                    time: 0,
+                    dwExtraInfo: 0,
+                },
+            },
+        };
+
+        let inputs = [move_input, down_input, up_input];
+        let result = SendInput(&inputs, std::mem::size_of::<INPUT>() as i32);
+
+        if result != inputs.len() as u32 {
+            return Err(format!(
+                "SendInput for click at ({x},{y}) sent {result}/{} events — some may have been blocked by UIPI",
+                inputs.len()
+            ));
+        }
+
+        Ok(())
+    }
+}
+
+#[cfg(windows)]
+pub fn type_text(text: &str) -> Result<(), String> {
+    use windows::Win32::UI::Input::KeyboardAndMouse::{
+        SendInput, INPUT, INPUT_KEYBOARD, KEYBDINPUT, KEYEVENTF_UNICODE,
+    };
+
+    if text.is_empty() {
+        return Ok(());
+    }
+
+    unsafe {
+        let mut inputs: Vec<INPUT> = Vec::with_capacity(text.len() * 2);
+
+        for ch in text.encode_utf16() {
+            // Key down
+            inputs.push(INPUT {
+                r#type: INPUT_KEYBOARD,
+                Anonymous: windows::Win32::UI::Input::KeyboardAndMouse::INPUT_0 {
+                    ki: KEYBDINPUT {
+                        wVk: windows::Win32::UI::Input::KeyboardAndMouse::VIRTUAL_KEY(0),
+                        wScan: ch,
+                        dwFlags: KEYEVENTF_UNICODE,
+                        time: 0,
+                        dwExtraInfo: 0,
+                    },
+                },
+            });
+            // Key up
+            inputs.push(INPUT {
+                r#type: INPUT_KEYBOARD,
+                Anonymous: windows::Win32::UI::Input::KeyboardAndMouse::INPUT_0 {
+                    ki: KEYBDINPUT {
+                        wVk: windows::Win32::UI::Input::KeyboardAndMouse::VIRTUAL_KEY(0),
+                        wScan: ch,
+                        dwFlags: KEYEVENTF_UNICODE
+                            | windows::Win32::UI::Input::KeyboardAndMouse::KEYEVENTF_KEYUP,
+                        time: 0,
+                        dwExtraInfo: 0,
+                    },
+                },
+            });
+        }
+
+        let result = SendInput(&inputs, std::mem::size_of::<INPUT>() as i32);
+
+        if result != inputs.len() as u32 {
+            return Err(format!(
+                "SendInput for type_text sent {result}/{} events — some may have been blocked (UIPI or secure desktop)",
+                inputs.len()
+            ));
+        }
+
+        Ok(())
+    }
+}
+
+#[cfg(not(windows))]
+pub fn click(_x: i32, _y: i32, _button: &MouseButton) -> Result<(), String> {
+    Err("click() is only supported on Windows".to_string())
+}
+
+#[cfg(not(windows))]
+pub fn type_text(_text: &str) -> Result<(), String> {
+    Err("type_text() is only supported on Windows".to_string())
+}
diff --git a/crates/client/src/main.rs b/crates/client/src/main.rs
index 8740dca..c3c72b3 100644
--- a/crates/client/src/main.rs
+++ b/crates/client/src/main.rs
@@ -1,7 +1,279 @@
-// helios-client — Phase 2 (not yet implemented)
-// See crates/client/README.md for the planned implementation.
+use std::path::PathBuf;
+use std::sync::Arc;
+use std::time::Duration;
 
-fn main() {
-    eprintln!("helios-client is not yet implemented. See crates/client/README.md.");
-    std::process::exit(1);
+use futures_util::{SinkExt, StreamExt};
+use serde::{Deserialize, Serialize};
+use tokio::sync::Mutex;
+use tokio_tungstenite::{connect_async, tungstenite::Message};
+use tracing::{error, info, warn};
+
+use helios_common::{ClientMessage, ServerMessage};
+
+mod shell;
+mod screenshot;
+mod input;
+
+#[derive(Debug, Serialize, Deserialize)]
+struct Config {
+    relay_url: String,
+    relay_code: String,
+    label: Option<String>,
+}
+
+impl Config {
+    fn config_path() -> PathBuf {
+        let base = dirs::config_dir()
+            .or_else(|| dirs::home_dir())
+            .unwrap_or_else(|| PathBuf::from("."));
+        base.join("helios-remote").join("config.json")
+    }
+
+    fn load() -> Option<Self> {
+        let path = Self::config_path();
+        let data = std::fs::read_to_string(&path).ok()?;
+        serde_json::from_str(&data).ok()
+    }
+
+    fn save(&self) -> std::io::Result<()> {
+        let path = Self::config_path();
+        std::fs::create_dir_all(path.parent().unwrap())?;
+        let data = serde_json::to_string_pretty(self).unwrap();
+        std::fs::write(&path, data)?;
+        Ok(())
+    }
+}
+
+fn prompt_config() -> Config {
+    let relay_url = {
+        println!("Relay server URL [default: ws://46.225.185.232:8765/ws]: ");
+        let mut input = String::new();
+        std::io::stdin().read_line(&mut input).unwrap();
+        let trimmed = input.trim();
+        if trimmed.is_empty() {
+            "ws://46.225.185.232:8765/ws".to_string()
+        } else {
+            trimmed.to_string()
+        }
+    };
+
+    let relay_code = {
+        println!("Enter relay code: ");
+        let mut input = String::new();
+        std::io::stdin().read_line(&mut input).unwrap();
+        input.trim().to_string()
+    };
+
+    let label = {
+        println!("Label for this machine (optional, press Enter to skip): ");
+        let mut input = String::new();
+        std::io::stdin().read_line(&mut input).unwrap();
+        let trimmed = input.trim().to_string();
+        if trimmed.is_empty() { None } else { Some(trimmed) }
+    };
+
+    Config { relay_url, relay_code, label }
+}
+
+#[tokio::main]
+async fn main() {
+    tracing_subscriber::fmt()
+        .with_env_filter(
+            std::env::var("RUST_LOG")
+                .unwrap_or_else(|_| "helios_client=info".to_string()),
+        )
+        .init();
+
+    // Load or prompt for config
+    let config = match Config::load() {
+        Some(c) => {
+            info!("Loaded config from {:?}", Config::config_path());
+            c
+        }
+        None => {
+            info!("No config found — prompting for setup");
+            let c = prompt_config();
+            if let Err(e) = c.save() {
+                error!("Failed to save config: {e}");
+            } else {
+                info!("Config saved to {:?}", Config::config_path());
+            }
+            c
+        }
+    };
+
+    let config = Arc::new(config);
+    let shell = Arc::new(Mutex::new(shell::PersistentShell::new()));
+
+    // Connect with exponential backoff
+    let mut backoff = Duration::from_secs(1);
+    const MAX_BACKOFF: Duration = Duration::from_secs(30);
+
+    loop {
+        info!("Connecting to {}", config.relay_url);
+        match connect_async(&config.relay_url).await {
+            Ok((ws_stream, _)) => {
+                info!("Connected!");
+                backoff = Duration::from_secs(1); // reset on success
+
+                let (mut write, mut read) = ws_stream.split();
+
+                // Send Hello
+                let hello = ClientMessage::Hello {
+                    label: config.label.clone(),
+                };
+                let hello_json = serde_json::to_string(&hello).unwrap();
+                if let Err(e) = write.send(Message::Text(hello_json)).await {
+                    error!("Failed to send Hello: {e}");
+                    tokio::time::sleep(backoff).await;
+                    backoff = (backoff * 2).min(MAX_BACKOFF);
+                    continue;
+                }
+
+                // Shared write half
+                let write = Arc::new(Mutex::new(write));
+
+                // Process messages
+                while let Some(msg_result) = read.next().await {
+                    match msg_result {
+                        Ok(Message::Text(text)) => {
+                            let server_msg: ServerMessage = match serde_json::from_str(&text) {
+                                Ok(m) => m,
+                                Err(e) => {
+                                    warn!("Failed to parse server message: {e}\nRaw: {text}");
+                                    continue;
+                                }
+                            };
+
+                            let write_clone = Arc::clone(&write);
+                            let shell_clone = Arc::clone(&shell);
+
+                            tokio::spawn(async move {
+                                let response = handle_message(server_msg, shell_clone).await;
+                                let json = serde_json::to_string(&response).unwrap();
+                                let mut w = write_clone.lock().await;
+                                if let Err(e) = w.send(Message::Text(json)).await {
+                                    error!("Failed to send response: {e}");
+                                }
+                            });
+                        }
+                        Ok(Message::Ping(data)) => {
+                            let mut w = write.lock().await;
+                            let _ = w.send(Message::Pong(data)).await;
+                        }
+                        Ok(Message::Close(_)) => {
+                            info!("Server closed connection");
+                            break;
+                        }
+                        Err(e) => {
+                            error!("WebSocket error: {e}");
+                            break;
+                        }
+                        _ => {}
+                    }
+                }
+
+                warn!("Disconnected. Reconnecting in {:?}...", backoff);
+            }
+            Err(e) => {
+                error!("Connection failed: {e}");
+            }
+        }
+
+        tokio::time::sleep(backoff).await;
+        backoff = (backoff * 2).min(MAX_BACKOFF);
+    }
+}
+
+async fn handle_message(
+    msg: ServerMessage,
+    shell: Arc<Mutex<shell::PersistentShell>>,
+) -> ClientMessage {
+    match msg {
+        ServerMessage::ScreenshotRequest { request_id } => {
+            match screenshot::take_screenshot() {
+                Ok((image_base64, width, height)) => ClientMessage::ScreenshotResponse {
+                    request_id,
+                    image_base64,
+                    width,
+                    height,
+                },
+                Err(e) => {
+                    error!("Screenshot failed: {e}");
+                    ClientMessage::Error {
+                        request_id,
+                        message: format!("Screenshot failed: {e}"),
+                    }
+                }
+            }
+        }
+
+        ServerMessage::ExecRequest { request_id, command } => {
+            info!("Exec: {command}");
+            let mut sh = shell.lock().await;
+            match sh.run(&command).await {
+                Ok((stdout, stderr, exit_code)) => ClientMessage::ExecResponse {
+                    request_id,
+                    stdout,
+                    stderr,
+                    exit_code,
+                },
+                Err(e) => {
+                    error!("Exec failed for command {:?}: {e}", command);
+                    ClientMessage::Error {
+                        request_id,
+                        message: format!(
+                            "Exec failed for command {:?}.\nError: {e}\nContext: persistent shell may have died.",
+                            command
+                        ),
+                    }
+                }
+            }
+        }
+
+        ServerMessage::ClickRequest { request_id, x, y, button } => {
+            info!("Click: ({x},{y}) {:?}", button);
+            match input::click(x, y, &button) {
+                Ok(()) => ClientMessage::Ack { request_id },
+                Err(e) => {
+                    error!("Click failed at ({x},{y}): {e}");
+                    ClientMessage::Error {
+                        request_id,
+                        message: format!("Click at ({x},{y}) failed: {e}"),
+                    }
+                }
+            }
+        }
+
+        ServerMessage::TypeRequest { request_id, text } => {
+            info!("Type: {} chars", text.len());
+            match input::type_text(&text) {
+                Ok(()) => ClientMessage::Ack { request_id },
+                Err(e) => {
+                    error!("Type failed: {e}");
+                    ClientMessage::Error {
+                        request_id,
+                        message: format!("Type failed: {e}"),
+                    }
+                }
+            }
+        }
+
+        ServerMessage::Ack { request_id } => {
+            info!("Server ack for {request_id}");
+            // Nothing to do - server acked something we sent
+            ClientMessage::Ack { request_id }
+        }
+
+        ServerMessage::Error { request_id, message } => {
+            error!("Server error (req={request_id:?}): {message}");
+            // No meaningful response needed but we need to return something
+            // Use a dummy ack if we have a request_id
+            if let Some(rid) = request_id {
+                ClientMessage::Ack { request_id: rid }
+            } else {
+                ClientMessage::Hello { label: None }
+            }
+        }
+    }
 }
diff --git a/crates/client/src/screenshot.rs b/crates/client/src/screenshot.rs
new file mode 100644
index 0000000..d867ea4
--- /dev/null
+++ b/crates/client/src/screenshot.rs
@@ -0,0 +1,146 @@
+/// Screenshot capture — Windows GDI on Windows, stub on other platforms.
+use base64::Engine;
+
+#[cfg(windows)]
+pub fn take_screenshot() -> Result<(String, u32, u32), String> {
+    use windows::Win32::Foundation::RECT;
+    use windows::Win32::Graphics::Gdi::{
+        BitBlt, CreateCompatibleBitmap, CreateCompatibleDC, DeleteDC, DeleteObject,
+        GetDIBits, GetObjectW, SelectObject, BITMAP, BITMAPINFO, BITMAPINFOHEADER,
+        DIB_RGB_COLORS, SRCCOPY,
+    };
+    use windows::Win32::UI::WindowsAndMessaging::GetDesktopWindow;
+    use windows::Win32::Graphics::Gdi::GetWindowDC;
+    use windows::Win32::Graphics::Gdi::ReleaseDC;
+
+    unsafe {
+        let hwnd = GetDesktopWindow();
+        let hdc_screen = GetWindowDC(hwnd);
+        if hdc_screen.is_invalid() {
+            return Err("GetWindowDC failed — cannot capture screen".to_string());
+        }
+
+        // Get screen dimensions
+        use windows::Win32::Graphics::Gdi::{GetDeviceCaps, HORZRES, VERTRES};
+        let width = GetDeviceCaps(hdc_screen, HORZRES) as u32;
+        let height = GetDeviceCaps(hdc_screen, VERTRES) as u32;
+
+        if width == 0 || height == 0 {
+            ReleaseDC(hwnd, hdc_screen);
+            return Err(format!("Invalid screen dimensions: {width}x{height}"));
+        }
+
+        // Create compatible DC and bitmap
+        let hdc_mem = CreateCompatibleDC(hdc_screen);
+        if hdc_mem.is_invalid() {
+            ReleaseDC(hwnd, hdc_screen);
+            return Err("CreateCompatibleDC failed".to_string());
+        }
+
+        let hbm = CreateCompatibleBitmap(hdc_screen, width as i32, height as i32);
+        if hbm.is_invalid() {
+            DeleteDC(hdc_mem);
+            ReleaseDC(hwnd, hdc_screen);
+            return Err("CreateCompatibleBitmap failed".to_string());
+        }
+
+        let old_obj = SelectObject(hdc_mem, hbm);
+
+        // BitBlt the screen into our bitmap
+        let blt_result = BitBlt(
+            hdc_mem,
+            0, 0,
+            width as i32, height as i32,
+            hdc_screen,
+            0, 0,
+            SRCCOPY,
+        );
+
+        if blt_result.is_err() {
+            SelectObject(hdc_mem, old_obj);
+            DeleteObject(hbm);
+            DeleteDC(hdc_mem);
+            ReleaseDC(hwnd, hdc_screen);
+            return Err("BitBlt failed — could not copy screen pixels".to_string());
+        }
+
+        // Get raw pixel data via GetDIBits
+        let mut bmi = BITMAPINFO {
+            bmiHeader: BITMAPINFOHEADER {
+                biSize: std::mem::size_of::<BITMAPINFOHEADER>() as u32,
+                biWidth: width as i32,
+                biHeight: -(height as i32), // negative = top-down
+                biPlanes: 1,
+                biBitCount: 32,
+                biCompression: 0, // BI_RGB
+                biSizeImage: 0,
+                biXPelsPerMeter: 0,
+                biYPelsPerMeter: 0,
+                biClrUsed: 0,
+                biClrImportant: 0,
+            },
+            bmiColors: [Default::default()],
+        };
+
+        let buf_size = (width * height * 4) as usize;
+        let mut pixel_buf: Vec<u8> = vec![0u8; buf_size];
+
+        let lines = GetDIBits(
+            hdc_mem,
+            hbm,
+            0,
+            height,
+            Some(pixel_buf.as_mut_ptr() as *mut _),
+            &mut bmi,
+            DIB_RGB_COLORS,
+        );
+
+        SelectObject(hdc_mem, old_obj);
+        DeleteObject(hbm);
+        DeleteDC(hdc_mem);
+        ReleaseDC(hwnd, hdc_screen);
+
+        if lines == 0 {
+            return Err(format!("GetDIBits failed — returned 0 scan lines (expected {height})"));
+        }
+
+        // Convert BGRA → RGBA
+        for chunk in pixel_buf.chunks_exact_mut(4) {
+            chunk.swap(0, 2); // B <-> R
+        }
+
+        // Encode as PNG
+        let png_bytes = encode_png(&pixel_buf, width, height)?;
+        let b64 = base64::engine::general_purpose::STANDARD.encode(&png_bytes);
+
+        Ok((b64, width, height))
+    }
+}
+
+#[cfg(not(windows))]
+pub fn take_screenshot() -> Result<(String, u32, u32), String> {
+    // Stub for non-Windows builds
+    // In a real scenario, could use X11/scrot on Linux
+    let width = 1u32;
+    let height = 1u32;
+    let pixel_data = vec![0u8, 0u8, 0u8, 255u8]; // single black pixel RGBA
+    let png_bytes = encode_png(&pixel_data, width, height)?;
+    let b64 = base64::engine::general_purpose::STANDARD.encode(&png_bytes);
+    Ok((b64, width, height))
+}
+
+fn encode_png(rgba: &[u8], width: u32, height: u32) -> Result<Vec<u8>, String> {
+    let mut buf = Vec::new();
+    {
+        let mut encoder = png::Encoder::new(&mut buf, width, height);
+        encoder.set_color(png::ColorType::Rgba);
+        encoder.set_depth(png::BitDepth::Eight);
+        let mut writer = encoder
+            .write_header()
+            .map_err(|e| format!("PNG header error: {e}"))?;
+        writer
+            .write_image_data(rgba)
+            .map_err(|e| format!("PNG write error: {e}"))?;
+    }
+    Ok(buf)
+}
diff --git a/crates/client/src/shell.rs b/crates/client/src/shell.rs
new file mode 100644
index 0000000..39addca
--- /dev/null
+++ b/crates/client/src/shell.rs
@@ -0,0 +1,161 @@
+/// Persistent shell session that keeps a cmd.exe (Windows) or sh (Unix) alive
+/// between commands, so state like `cd` is preserved.
+use std::process::Stdio;
+use tokio::io::{AsyncBufReadExt, AsyncWriteExt, BufReader};
+use tokio::process::{Child, ChildStdin, ChildStdout, ChildStderr};
+use tracing::{debug, warn};
+
+const OUTPUT_TIMEOUT_MS: u64 = 10_000;
+/// Unique sentinel appended after every command to know when output is done.
+const SENTINEL: &str = "__HELIOS_DONE__";
+
+pub struct PersistentShell {
+    child: Option<ShellProcess>,
+}
+
+struct ShellProcess {
+    _child: Child,
+    stdin: ChildStdin,
+    stdout_lines: tokio::sync::Mutex<BufReader<ChildStdout>>,
+    stderr_lines: tokio::sync::Mutex<BufReader<ChildStderr>>,
+}
+
+impl PersistentShell {
+    pub fn new() -> Self {
+        Self { child: None }
+    }
+
+    async fn spawn(&mut self) -> Result<(), String> {
+        #[cfg(windows)]
+        let (program, args) = ("cmd.exe", vec!["/Q"]);
+        #[cfg(not(windows))]
+        let (program, args) = ("sh", vec!["-s"]);
+
+        let mut cmd = tokio::process::Command::new(program);
+        for arg in &args {
+            cmd.arg(arg);
+        }
+        cmd.stdin(Stdio::piped())
+            .stdout(Stdio::piped())
+            .stderr(Stdio::piped())
+            .kill_on_drop(true);
+
+        let mut child = cmd
+            .spawn()
+            .map_err(|e| format!("Failed to spawn shell '{program}': {e}"))?;
+
+        let stdin = child.stdin.take().ok_or("no stdin")?;
+        let stdout = child.stdout.take().ok_or("no stdout")?;
+        let stderr = child.stderr.take().ok_or("no stderr")?;
+
+        self.child = Some(ShellProcess {
+            _child: child,
+            stdin,
+            stdout_lines: tokio::sync::Mutex::new(BufReader::new(stdout)),
+            stderr_lines: tokio::sync::Mutex::new(BufReader::new(stderr)),
+        });
+
+        Ok(())
+    }
+
+    /// Run a command in the persistent shell, returning (stdout, stderr, exit_code).
+    /// exit_code is always 0 for intermediate commands; we read the exit code via `echo %ERRORLEVEL%`.
+    pub async fn run(&mut self, command: &str) -> Result<(String, String, i32), String> {
+        // Restart shell if it died
+        if self.child.is_none() {
+            self.spawn().await?;
+        }
+
+        let result = self.run_inner(command).await;
+
+        match result {
+            Ok(r) => Ok(r),
+            Err(e) => {
+                // Shell probably died — drop it and report error
+                warn!("Shell error, will respawn next time: {e}");
+                self.child = None;
+                Err(e)
+            }
+        }
+    }
+
+    async fn run_inner(&mut self, command: &str) -> Result<(String, String, i32), String> {
+        let shell = self.child.as_mut().ok_or("no shell")?;
+
+        // Write command + sentinel echo to stdin
+        #[cfg(windows)]
+        let cmd_line = format!("{command}\r\necho {SENTINEL}%ERRORLEVEL%\r\n");
+        #[cfg(not(windows))]
+        let cmd_line = format!("{command}\necho {SENTINEL}$?\n");
+
+        debug!("Shell input: {cmd_line:?}");
+
+        shell
+            .stdin
+            .write_all(cmd_line.as_bytes())
+            .await
+            .map_err(|e| format!("Failed to write to shell stdin: {e}"))?;
+        shell
+            .stdin
+            .flush()
+            .await
+            .map_err(|e| format!("Failed to flush shell stdin: {e}"))?;
+
+        // Read stdout until we see the sentinel line
+        let mut stdout_buf = String::new();
+        #[allow(unused_assignments)]
+        let mut exit_code = 0i32;
+
+        let timeout = tokio::time::Duration::from_millis(OUTPUT_TIMEOUT_MS);
+
+        {
+            let mut reader = shell.stdout_lines.lock().await;
+            loop {
+                let mut line = String::new();
+                let read_fut = reader.read_line(&mut line);
+                match tokio::time::timeout(timeout, read_fut).await {
+                    Ok(Ok(0)) => {
+                        return Err("Shell stdout EOF — process likely died".to_string());
+                    }
+                    Ok(Ok(_)) => {
+                        debug!("stdout line: {line:?}");
+                        if line.trim_end().starts_with(SENTINEL) {
+                            // Parse exit code from sentinel line
+                            let code_str = line.trim_end().trim_start_matches(SENTINEL);
+                            exit_code = code_str.trim().parse().unwrap_or(0);
+                            break;
+                        } else {
+                            stdout_buf.push_str(&line);
+                        }
+                    }
+                    Ok(Err(e)) => {
+                        return Err(format!("Shell stdout read error: {e}"));
+                    }
+                    Err(_) => {
+                        return Err(format!(
+                            "Shell stdout timed out after {}ms waiting for command to finish.\nCommand: {command}\nOutput so far: {stdout_buf}",
+                            OUTPUT_TIMEOUT_MS
+                        ));
+                    }
+                }
+            }
+        }
+
+        // Drain available stderr (non-blocking)
+        let mut stderr_buf = String::new();
+        {
+            let mut reader = shell.stderr_lines.lock().await;
+            let drain_timeout = tokio::time::Duration::from_millis(100);
+            loop {
+                let mut line = String::new();
+                match tokio::time::timeout(drain_timeout, reader.read_line(&mut line)).await {
+                    Ok(Ok(0)) | Err(_) => break,
+                    Ok(Ok(_)) => stderr_buf.push_str(&line),
+                    Ok(Err(_)) => break,
+                }
+            }
+        }
+
+        Ok((stdout_buf, stderr_buf, exit_code))
+    }
+}