Merge pull request 'colors-rewrite' (#1) from colors-rewrite into master

Reviewed-on: #1

.github/workflows/ci.yml

@@ -63,6 +63,7 @@ jobs:
     steps:
       - uses: actions/checkout@v4
       - uses: dtolnay/rust-toolchain@stable
+      - run: cargo build -p pty-mock
       - run: cargo test --all-targets
 
   test:

Cargo.toml

@@ -2,6 +2,7 @@
 resolver = "2"
 members = [
     "crates/claude-chill",
+    "crates/pty-mock",
 ]
 
 [workspace.package]

crates/claude-chill/Cargo.toml

@@ -25,7 +25,7 @@ nix = { version = "0.30", features = ["term", "signal", "poll", "process", "fs"]
 libc = "0.2"
 serde = { version = "1", features = ["derive"] }
 toml = "0.8"
-vt100 = "0.16"
-termwiz = "0.23"
+termwiz = { git = "https://github.com/wezterm/wezterm", rev = "577474d89ee61aef4a48145cdec82a638d874751" }
+wezterm-term = { git = "https://github.com/wezterm/wezterm", rev = "577474d89ee61aef4a48145cdec82a638d874751" }
 log = "0.4"
 env_logger = "0.11"

crates/claude-chill/src/color_preservation_tests.rs

@@ -0,0 +1,216 @@
+//! Color / SGR / hyperlink preservation tests.
+//!
+//! These tests feed modern terminal styling bytes through a real `Proxy`,
+//! force a render, capture what the proxy emits to its stdout side, and
+//! assert that the styling survives the round-trip.
+//!
+//! After the swap from `vt100 0.16` to `wezterm-term` + `termwiz` Surface
+//! diffing, most of the modern attribute set is preserved end-to-end:
+//! OSC 8 hyperlinks, strikethrough, double underline, and truecolor all
+//! round-trip. Two known gaps remain — both are limitations of termwiz's
+//! `TerminfoRenderer`, not of the cell model:
+//!
+//!   * Curly / dotted / dashed underline styles (`SGR 4:3`, `4:4`, `4:5`):
+//!     stored on the cell, never emitted on render.
+//!   * Underline color (`SGR 58`): stored on the cell, never emitted on
+//!     render.
+//!
+//! Tests for those two are kept `#[ignore]` so CI stays green. They will
+//! pass if/when termwiz's renderer learns to emit them (or we replace
+//! the emit step with a custom serializer).
+
+#[cfg(test)]
+mod tests {
+    use crate::proxy::{Proxy, ProxyConfig};
+    use nix::fcntl::{FcntlArg, OFlag, fcntl};
+    use nix::pty::openpty;
+    use nix::sys::termios::{self, SetArg};
+    use nix::unistd::{pipe, read};
+    use std::os::fd::{AsFd, AsRawFd, OwnedFd};
+    use std::os::unix::process::CommandExt;
+    use std::process::{Child, Command};
+
+    fn pty_mock_binary() -> Option<String> {
+        let manifest_dir = env!("CARGO_MANIFEST_DIR");
+        let bin = format!("{}/../../target/debug/pty-mock", manifest_dir);
+        if std::path::Path::new(&bin).exists() {
+            Some(bin)
+        } else {
+            None
+        }
+    }
+
+    fn spawn_echo_child() -> Option<(OwnedFd, Child)> {
+        let bin = pty_mock_binary()?;
+        let pty = openpty(None, None).expect("openpty failed");
+
+        let slave_fd = pty.slave.as_raw_fd();
+        let mut termios_settings = termios::tcgetattr(&pty.slave).expect("tcgetattr failed");
+        termios::cfmakeraw(&mut termios_settings);
+        termios::tcsetattr(&pty.slave, SetArg::TCSANOW, &termios_settings)
+            .expect("tcsetattr failed");
+
+        let child = unsafe {
+            Command::new(&bin)
+                .arg("echo")
+                .stdin(pty.slave.try_clone().expect("clone slave"))
+                .stdout(pty.slave.try_clone().expect("clone slave"))
+                .stderr(pty.slave.try_clone().expect("clone slave"))
+                .pre_exec(move || {
+                    if libc::setsid() == -1 {
+                        return Err(std::io::Error::last_os_error());
+                    }
+                    if libc::ioctl(slave_fd, libc::TIOCSCTTY as libc::c_ulong, 0) == -1 {
+                        return Err(std::io::Error::last_os_error());
+                    }
+                    Ok(())
+                })
+                .spawn()
+                .expect("failed to spawn pty-mock echo")
+        };
+
+        drop(pty.slave);
+
+        let flags = fcntl(&pty.master, FcntlArg::F_GETFL).expect("F_GETFL");
+        let flags = OFlag::from_bits_truncate(flags);
+        fcntl(&pty.master, FcntlArg::F_SETFL(flags | OFlag::O_NONBLOCK)).expect("F_SETFL");
+
+        Some((pty.master, child))
+    }
+
+    fn make_proxy(master: OwnedFd, child: Child) -> Proxy {
+        Proxy::new_for_test(master, child, ProxyConfig::default(), 24, 80)
+    }
+
+    /// Make a non-blocking pipe to capture proxy output.
+    fn capture_pipe() -> (OwnedFd, OwnedFd) {
+        let (rx, tx) = pipe().expect("pipe failed");
+        let flags = fcntl(&rx, FcntlArg::F_GETFL).expect("F_GETFL");
+        let flags = OFlag::from_bits_truncate(flags);
+        fcntl(&rx, FcntlArg::F_SETFL(flags | OFlag::O_NONBLOCK)).expect("F_SETFL");
+        (rx, tx)
+    }
+
+    fn drain(rx: &OwnedFd) -> Vec<u8> {
+        let mut buf = [0u8; 65536];
+        let mut out = Vec::new();
+        loop {
+            match read(rx.as_fd(), &mut buf) {
+                Ok(0) => break,
+                Ok(n) => out.extend_from_slice(&buf[..n]),
+                Err(_) => break,
+            }
+        }
+        out
+    }
+
+    /// Feed `input` through the proxy, force a render to a captured pipe,
+    /// and return what the proxy emitted.
+    fn render_and_capture(input: &[u8]) -> Option<Vec<u8>> {
+        let (master, child) = spawn_echo_child()?;
+        let mut proxy = make_proxy(master, child);
+        let (rx, tx) = capture_pipe();
+
+        proxy.process_output(input, &tx).expect("process_output");
+        proxy.force_render(&tx).expect("force_render");
+
+        Some(drain(&rx))
+    }
+
+    fn contains_bytes(haystack: &[u8], needle: &[u8]) -> bool {
+        haystack.windows(needle.len()).any(|w| w == needle)
+    }
+
+    #[test]
+    fn osc8_hyperlink_survives_render() {
+        // OSC 8 hyperlinks — used for clickable file paths / URLs.
+        // Format: ESC ] 8 ; ; URL ESC \ ... ESC ] 8 ; ; ESC \
+        let mut input = Vec::new();
+        input.extend_from_slice(b"\x1b]8;;https://example.com/foo\x1b\\");
+        input.extend_from_slice(b"link text");
+        input.extend_from_slice(b"\x1b]8;;\x1b\\");
+
+        let captured = render_and_capture(&input).expect("pty-mock binary missing");
+        assert!(
+            contains_bytes(&captured, b"\x1b]8;;https://example.com/foo"),
+            "OSC 8 hyperlink open should survive render, got: {:?}",
+            String::from_utf8_lossy(&captured)
+        );
+        assert!(
+            contains_bytes(&captured, b"\x1b]8;;\x1b\\"),
+            "OSC 8 hyperlink close should survive render, got: {:?}",
+            String::from_utf8_lossy(&captured)
+        );
+    }
+
+    #[test]
+    fn strikethrough_survives_render() {
+        // SGR 9 = strikethrough. vt100 0.16 has no field for it.
+        let input = b"\x1b[9mstruck through text\x1b[0m";
+        let captured = render_and_capture(input).expect("pty-mock binary missing");
+        assert!(
+            contains_bytes(&captured, b"\x1b[9m") || contains_bytes(&captured, b";9m"),
+            "SGR 9 strikethrough should survive render, got: {:?}",
+            String::from_utf8_lossy(&captured)
+        );
+    }
+
+    #[test]
+    #[ignore] // termwiz TerminfoRenderer only emits Single/Double underline.
+    fn curly_underline_survives_render() {
+        // SGR 4:3 = curly underline (kitty/wezterm/ghostty all support).
+        let input = b"\x1b[4:3mcurly underline\x1b[0m";
+        let captured = render_and_capture(input).expect("pty-mock binary missing");
+        assert!(
+            contains_bytes(&captured, b"4:3"),
+            "SGR 4:3 curly underline should survive render, got: {:?}",
+            String::from_utf8_lossy(&captured)
+        );
+    }
+
+    #[test]
+    #[ignore] // termwiz TerminfoRenderer doesn't emit SGR 58 underline color.
+    fn underline_color_survives_render() {
+        // SGR 58:2::R:G:B = truecolor underline color.
+        let input = b"\x1b[4m\x1b[58:2::255:0:0mcolored underline\x1b[0m";
+        let captured = render_and_capture(input).expect("pty-mock binary missing");
+        assert!(
+            contains_bytes(&captured, b"58:2") || contains_bytes(&captured, b"58;2"),
+            "SGR 58 underline color should survive render, got: {:?}",
+            String::from_utf8_lossy(&captured)
+        );
+    }
+
+    #[test]
+    fn double_underline_survives_render() {
+        // SGR 21 = doubly underlined.
+        let input = b"\x1b[21mdouble underlined\x1b[0m";
+        let captured = render_and_capture(input).expect("pty-mock binary missing");
+        assert!(
+            contains_bytes(&captured, b"\x1b[21m")
+                || contains_bytes(&captured, b";21m")
+                || contains_bytes(&captured, b"4:2"),
+            "SGR 21 double underline should survive render, got: {:?}",
+            String::from_utf8_lossy(&captured)
+        );
+    }
+
+    /// Sanity check: confirm a styling attribute that vt100 *does* support
+    /// already survives the render. If this ever fails, something more
+    /// fundamental is broken than just attribute coverage.
+    #[test]
+    fn truecolor_foreground_survives_render() {
+        // SGR 38;2;R;G;B = truecolor foreground. vt100 supports this.
+        let input = b"\x1b[38;2;255;128;0morange text\x1b[0m";
+        let Some(captured) = render_and_capture(input) else {
+            // pty-mock not built — skip.
+            return;
+        };
+        assert!(
+            contains_bytes(&captured, b"38;2;255;128;0")
+                || contains_bytes(&captured, b"38:2::255:128:0"),
+            "truecolor foreground should survive render (sanity), got: {:?}",
+            String::from_utf8_lossy(&captured)
+        );
+    }
+}

crates/claude-chill/src/integration_tests.rs

@@ -0,0 +1,539 @@
+#[cfg(test)]
+mod tests {
+    use crate::proxy::{Proxy, ProxyConfig};
+    use nix::fcntl::{FcntlArg, OFlag, fcntl};
+    use nix::poll::{PollFd, PollFlags, PollTimeout, poll};
+    use nix::pty::openpty;
+    use nix::sys::termios::{self, SetArg};
+    use nix::unistd::read;
+    use std::os::fd::{AsFd, AsRawFd, FromRawFd, OwnedFd};
+    use std::os::unix::process::CommandExt;
+    use std::process::{Child, Command};
+    use std::time::Duration;
+
+    fn pty_mock_binary() -> Option<String> {
+        let manifest_dir = env!("CARGO_MANIFEST_DIR");
+        let bin = format!("{}/../../target/debug/pty-mock", manifest_dir);
+        if std::path::Path::new(&bin).exists() {
+            return Some(bin);
+        }
+        None
+    }
+
+    fn spawn_command(cmd: &str, args: &[&str]) -> (OwnedFd, Child) {
+        let pty = openpty(None, None).expect("openpty failed");
+
+        let slave_fd = pty.slave.as_raw_fd();
+        let mut termios_settings = termios::tcgetattr(&pty.slave).expect("tcgetattr failed");
+        termios::cfmakeraw(&mut termios_settings);
+        termios::tcsetattr(&pty.slave, SetArg::TCSANOW, &termios_settings)
+            .expect("tcsetattr failed");
+
+        let child = unsafe {
+            Command::new(cmd)
+                .args(args)
+                .stdin(pty.slave.try_clone().expect("clone slave"))
+                .stdout(pty.slave.try_clone().expect("clone slave"))
+                .stderr(pty.slave.try_clone().expect("clone slave"))
+                .pre_exec(move || {
+                    if libc::setsid() == -1 {
+                        return Err(std::io::Error::last_os_error());
+                    }
+                    if libc::ioctl(slave_fd, libc::TIOCSCTTY as libc::c_ulong, 0) == -1 {
+                        return Err(std::io::Error::last_os_error());
+                    }
+                    Ok(())
+                })
+                .spawn()
+                .expect("failed to spawn command")
+        };
+
+        drop(pty.slave);
+
+        // Set master to non-blocking
+        let flags = fcntl(&pty.master, FcntlArg::F_GETFL).expect("F_GETFL");
+        let flags = OFlag::from_bits_truncate(flags);
+        fcntl(&pty.master, FcntlArg::F_SETFL(flags | OFlag::O_NONBLOCK)).expect("F_SETFL");
+
+        (pty.master, child)
+    }
+
+    fn spawn_mock(subcommand: &str) -> Option<(OwnedFd, Child)> {
+        let bin = pty_mock_binary()?;
+        Some(spawn_command(&bin, &[subcommand]))
+    }
+
+    fn read_pty_output(master: &OwnedFd, timeout_ms: u16) -> Vec<u8> {
+        let mut result = Vec::new();
+        let mut buf = [0u8; 65536];
+        let mut poll_fds = [PollFd::new(master.as_fd(), PollFlags::POLLIN)];
+
+        loop {
+            match poll(&mut poll_fds, PollTimeout::from(timeout_ms)) {
+                Ok(0) => break,
+                Ok(_) => match read(master.as_fd(), &mut buf) {
+                    Ok(0) => break,
+                    Ok(n) => result.extend_from_slice(&buf[..n]),
+                    Err(nix::errno::Errno::EAGAIN) => break,
+                    Err(_) => break,
+                },
+                Err(_) => break,
+            }
+        }
+        result
+    }
+
+    fn make_proxy(master: OwnedFd, child: Child) -> Proxy {
+        let config = ProxyConfig::default();
+        Proxy::new_for_test(master, child, config, 24, 80)
+    }
+
+    fn dev_null() -> OwnedFd {
+        use std::fs::OpenOptions;
+        let f = OpenOptions::new()
+            .write(true)
+            .open("/dev/null")
+            .expect("open /dev/null");
+        OwnedFd::from(f)
+    }
+
+    fn dup_master(proxy: &Proxy) -> OwnedFd {
+        let raw = proxy.pty_master_fd_raw();
+        unsafe { OwnedFd::from_raw_fd(libc::dup(raw)) }
+    }
+
+    #[test]
+    fn test_echo_baseline() {
+        let Some((master, child)) = spawn_mock("echo") else {
+            return;
+        };
+        let mut proxy = make_proxy(master, child);
+        let sink = dev_null();
+
+        proxy
+            .process_input(b"hello world\r\n", &sink)
+            .expect("process_input");
+        proxy.flush_drain_buffer(&sink).expect("flush drain");
+
+        std::thread::sleep(Duration::from_millis(50));
+
+        let master_dup = dup_master(&proxy);
+        let output = read_pty_output(&master_dup, 100);
+        assert!(!output.is_empty(), "expected output from echo child");
+        proxy
+            .process_output(&output, &sink)
+            .expect("process_output");
+
+        let mut history = Vec::new();
+        proxy.history().append_all(&mut history);
+        let history_str = String::from_utf8_lossy(&history);
+        assert!(
+            history_str.contains("hello world"),
+            "history should contain echoed text, got: {:?}",
+            history_str
+        );
+    }
+
+    #[test]
+    fn test_alt_screen_tracking() {
+        let Some((master, child)) = spawn_mock("alt-screen") else {
+            return;
+        };
+        let mut proxy = make_proxy(master, child);
+        let sink = dev_null();
+
+        std::thread::sleep(Duration::from_millis(50));
+
+        let master_dup = dup_master(&proxy);
+        let output = read_pty_output(&master_dup, 100);
+        if !output.is_empty() {
+            proxy
+                .process_output(&output, &sink)
+                .expect("process_output");
+        }
+
+        assert!(
+            proxy.is_in_alternate_screen(),
+            "proxy should be in alt screen"
+        );
+
+        proxy.process_input(b"x", &sink).expect("process_input");
+        proxy.flush_drain_buffer(&sink).expect("flush drain");
+
+        std::thread::sleep(Duration::from_millis(50));
+
+        let master_dup = dup_master(&proxy);
+        let output = read_pty_output(&master_dup, 100);
+        if !output.is_empty() {
+            proxy
+                .process_output(&output, &sink)
+                .expect("process_output");
+        }
+
+        assert!(
+            !proxy.is_in_alternate_screen(),
+            "proxy should have exited alt screen"
+        );
+    }
+
+    #[test]
+    fn test_bracketed_paste_flow() {
+        let Some((master, child)) = spawn_mock("paste-echo") else {
+            return;
+        };
+        let mut proxy = make_proxy(master, child);
+        let sink = dev_null();
+
+        std::thread::sleep(Duration::from_millis(50));
+        let master_dup = dup_master(&proxy);
+        let output = read_pty_output(&master_dup, 100);
+        if !output.is_empty() {
+            proxy
+                .process_output(&output, &sink)
+                .expect("process_output");
+        }
+
+        let mut paste = Vec::new();
+        paste.extend_from_slice(b"\x1b[200~");
+        paste.extend_from_slice(b"pasted content\r\n");
+        paste.extend_from_slice(b"\x1b[201~");
+
+        proxy.process_input(&paste, &sink).expect("process_input");
+        proxy.flush_drain_buffer(&sink).expect("flush drain");
+
+        assert!(
+            !proxy.is_in_bracketed_paste(),
+            "paste mode should be off after complete paste"
+        );
+    }
+
+    #[test]
+    fn test_split_paste_end_marker() {
+        let Some((master, child)) = spawn_mock("paste-echo") else {
+            return;
+        };
+        let mut proxy = make_proxy(master, child);
+        let sink = dev_null();
+
+        std::thread::sleep(Duration::from_millis(50));
+        let master_dup = dup_master(&proxy);
+        let output = read_pty_output(&master_dup, 100);
+        if !output.is_empty() {
+            proxy
+                .process_output(&output, &sink)
+                .expect("process_output");
+        }
+
+        let mut chunk1 = Vec::new();
+        chunk1.extend_from_slice(b"\x1b[200~");
+        chunk1.extend_from_slice(b"split test\r\n");
+        chunk1.extend_from_slice(b"\x1b[20"); // partial end marker
+
+        proxy
+            .process_input(&chunk1, &sink)
+            .expect("process_input chunk1");
+        proxy.flush_drain_buffer(&sink).expect("flush drain");
+
+        assert!(
+            proxy.is_in_bracketed_paste(),
+            "should still be in paste mode after partial end marker"
+        );
+
+        proxy
+            .process_input(b"1~", &sink)
+            .expect("process_input chunk2");
+        proxy.flush_drain_buffer(&sink).expect("flush drain");
+
+        assert!(
+            !proxy.is_in_bracketed_paste(),
+            "paste mode should be off after completing split end marker"
+        );
+    }
+
+    #[test]
+    fn test_alt_screen_exit_restores_main_content() {
+        let Some((master, child)) = spawn_mock("echo") else {
+            return;
+        };
+        let mut proxy = make_proxy(master, child);
+        let sink = dev_null();
+
+        // Simulate child writing main screen content
+        let main_content = b"Claude Code v2.1.84\r\nOpus 4.6\r\n~/public/claude-chill\r\n";
+        proxy
+            .process_output(main_content, &sink)
+            .expect("process_output main content");
+
+        let screen_before = proxy.vt_screen_text();
+        assert!(
+            screen_before.contains("Claude Code v2.1.84"),
+            "main content should be on screen before alt screen, got: {:?}",
+            screen_before
+        );
+
+        // Child enters alt screen
+        proxy
+            .process_output(b"\x1b[?1049h", &sink)
+            .expect("process_output alt enter");
+        assert!(proxy.is_in_alternate_screen());
+
+        // Child writes alt screen content (e.g. vim, less)
+        proxy
+            .process_output(b"alt screen editor content\r\nline 2\r\n", &sink)
+            .expect("process_output alt content");
+
+        // Child exits alt screen
+        proxy
+            .process_output(b"\x1b[?1049l", &sink)
+            .expect("process_output alt exit");
+        assert!(!proxy.is_in_alternate_screen());
+
+        // The VT parser should have restored the main screen content
+        let screen_after = proxy.vt_screen_text();
+        assert!(
+            screen_after.contains("Claude Code v2.1.84"),
+            "main content should be restored after alt screen exit, got: {:?}",
+            screen_after
+        );
+    }
+
+    // Skipped on this branch: depends on the alt-screen feed-order fix from
+    // upstream PR #35 (incremental VT feeding around alt enter/exit). We're
+    // pulling in only the test harness now; the semantic fix is a separate
+    // step. Re-enable by removing #[ignore] once that change lands.
+    #[test]
+    #[ignore]
+    fn test_alt_screen_exit_restores_after_clear_screen_sync_block() {
+        // Reproduces bug: sync block containing clear screen clears VT parser,
+        // but render_vt_screen never fires before alt-screen-enter arrives
+        // in the next chunk. VT parser saves blank screen. After alt exit,
+        // contents_formatted() paints blank over the real terminal which
+        // still had the original content (it never got the clear render).
+        let Some((master, child)) = spawn_mock("echo") else {
+            return;
+        };
+        let mut proxy = make_proxy(master, child);
+        let sink = dev_null();
+
+        // Initial content via sync block — this gets rendered
+        let mut initial_sync = Vec::new();
+        initial_sync.extend_from_slice(b"\x1b[?2026h");
+        initial_sync.extend_from_slice(b"\x1b[H");
+        initial_sync.extend_from_slice(b"Claude Code v2.1.84\r\n");
+        initial_sync.extend_from_slice(b"Opus 4.6\r\n");
+        initial_sync.extend_from_slice(b"~/public/claude-chill\r\n");
+        initial_sync.extend_from_slice(b"\x1b[?2026l");
+
+        proxy
+            .process_output(&initial_sync, &sink)
+            .expect("initial sync block");
+
+        let screen_before = proxy.vt_screen_text();
+        assert!(
+            screen_before.contains("Claude Code v2.1.84"),
+            "header should be on screen initially"
+        );
+
+        // Sync block with clear screen (simulates ctrl-g response) —
+        // VT parser processes the clear but render never fires
+        let mut clear_sync = Vec::new();
+        clear_sync.extend_from_slice(b"\x1b[?2026h");
+        clear_sync.extend_from_slice(b"\x1b[2J"); // clear screen
+        clear_sync.extend_from_slice(b"\x1b[H");
+        clear_sync.extend_from_slice(b"\x1b[?2026l");
+
+        proxy
+            .process_output(&clear_sync, &sink)
+            .expect("clear sync block");
+
+        // VT parser screen is now blank (clear screen was processed)
+        let screen_after_clear = proxy.vt_screen_text();
+        assert!(
+            !screen_after_clear.contains("Claude Code"),
+            "VT screen should be blank after clear sync block"
+        );
+
+        // Alt screen enter in the NEXT chunk — no render_vt_screen fired
+        // between the clear sync and this. VT parser saves blank screen.
+        proxy
+            .process_output(b"\x1b[?1049h", &sink)
+            .expect("alt screen enter");
+        assert!(proxy.is_in_alternate_screen());
+
+        // Editor content during alt screen
+        proxy
+            .process_output(b"editor content\r\n", &sink)
+            .expect("alt content");
+
+        // Alt screen exit — VT restores saved (blank) screen
+        proxy
+            .process_output(b"\x1b[?1049l", &sink)
+            .expect("alt screen exit");
+        assert!(!proxy.is_in_alternate_screen());
+
+        // Clear screen wiped the main buffer before alt-screen saved it.
+        // Correct VT100 behavior: restored screen should be blank.
+        let screen_after_exit = proxy.vt_screen_text();
+        assert!(
+            !screen_after_exit.contains("Claude Code v2.1.84"),
+            "header should NOT survive clear + alt screen round-trip, got: {:?}",
+            screen_after_exit
+        );
+    }
+
+    #[test]
+    fn test_sync_block_tracking() {
+        let Some((master, child)) = spawn_mock("echo") else {
+            return;
+        };
+        let mut proxy = make_proxy(master, child);
+        let sink = dev_null();
+
+        // Start a sync block without ending it
+        proxy
+            .process_output(b"\x1b[?2026h some content", &sink)
+            .expect("partial sync block");
+        assert!(
+            proxy.is_in_sync_block(),
+            "should be in sync block after SYNC_START without SYNC_END"
+        );
+
+        // End the sync block
+        proxy
+            .process_output(b" more content \x1b[?2026l", &sink)
+            .expect("sync block end");
+        assert!(
+            !proxy.is_in_sync_block(),
+            "should not be in sync block after SYNC_END"
+        );
+    }
+
+    #[test]
+    fn test_lookback_mode_toggle() {
+        let Some((master, child)) = spawn_mock("echo") else {
+            return;
+        };
+        let mut proxy = make_proxy(master, child);
+        let sink = dev_null();
+
+        // Generate some output so lookback has content
+        proxy
+            .process_output(b"line 1\r\nline 2\r\nline 3\r\n", &sink)
+            .expect("output");
+
+        assert!(!proxy.is_in_lookback_mode());
+
+        // Send legacy lookback key (0x1E = Ctrl+^)
+        send_input(&mut proxy, &sink, &[0x1E]);
+        assert!(
+            proxy.is_in_lookback_mode(),
+            "should enter lookback mode after Ctrl+^"
+        );
+
+        // Send it again to exit
+        send_input(&mut proxy, &sink, &[0x1E]);
+        assert!(
+            !proxy.is_in_lookback_mode(),
+            "should exit lookback mode after second Ctrl+^"
+        );
+    }
+
+    fn pump_proxy(proxy: &mut Proxy, sink: &OwnedFd, timeout_ms: u16) {
+        let master_dup = dup_master(proxy);
+        let output = read_pty_output(&master_dup, timeout_ms);
+        if !output.is_empty() {
+            proxy.process_output(&output, sink).expect("process_output");
+        }
+    }
+
+    fn send_input(proxy: &mut Proxy, sink: &OwnedFd, data: &[u8]) {
+        proxy.process_input(data, sink).expect("process_input");
+        proxy.flush_drain_buffer(sink).expect("flush drain");
+    }
+
+    fn wait_for_screen(proxy: &mut Proxy, sink: &OwnedFd, text: &str, timeout: Duration) -> bool {
+        let start = std::time::Instant::now();
+        while start.elapsed() < timeout {
+            pump_proxy(proxy, sink, 100);
+            if proxy.vt_screen_text().contains(text) {
+                return true;
+            }
+        }
+        false
+    }
+
+    #[test]
+    #[ignore] // requires claude CLI to be installed and authenticated
+    fn test_claude_alt_screen_restore() {
+        let (master, child) = spawn_command("claude", &[]);
+        let mut proxy = make_proxy(master, child);
+        let sink = dev_null();
+
+        // Wait for Claude Code to start up and show its UI
+        assert!(
+            wait_for_screen(&mut proxy, &sink, "Claude Code", Duration::from_secs(10)),
+            "Claude Code did not start, screen: {:?}",
+            proxy.vt_screen_text()
+        );
+
+        let screen_before = proxy.vt_screen_text();
+        eprintln!("Screen before alt screen:\n{}", screen_before);
+        assert!(
+            screen_before.contains("▐▛███▜▌"),
+            "logo should be present before alt screen"
+        );
+
+        // Send Ctrl-G to open the editor (enters alt screen)
+        send_input(&mut proxy, &sink, &[0x07]); // Ctrl-G
+
+        // Wait for alt screen to be entered
+        let start = std::time::Instant::now();
+        while start.elapsed() < Duration::from_secs(5) {
+            pump_proxy(&mut proxy, &sink, 100);
+            if proxy.is_in_alternate_screen() {
+                break;
+            }
+        }
+        assert!(
+            proxy.is_in_alternate_screen(),
+            "should have entered alt screen after Ctrl-G"
+        );
+
+        // Pump until editor has rendered
+        pump_proxy(&mut proxy, &sink, 500);
+
+        // Send :wq<Enter> to close the editor (exits alt screen)
+        send_input(&mut proxy, &sink, b"\x1b");
+        pump_proxy(&mut proxy, &sink, 100);
+        send_input(&mut proxy, &sink, b":wq\r");
+
+        // Wait for alt screen to be exited
+        let start = std::time::Instant::now();
+        while start.elapsed() < Duration::from_secs(5) {
+            pump_proxy(&mut proxy, &sink, 100);
+            if !proxy.is_in_alternate_screen() {
+                break;
+            }
+        }
+
+        // Drain remaining output after alt screen exit
+        pump_proxy(&mut proxy, &sink, 500);
+
+        let vt_screen_after = proxy.vt_screen_text();
+
+        eprintln!("VT parser screen after alt exit:\n{}", vt_screen_after);
+
+        // Claude Code bug: after editor exit, the logo (▐▛███▜▌) is not
+        // redrawn. This happens with or without claude-chill.
+        // Update this assertion if Claude Code fixes the redraw.
+        assert!(
+            !vt_screen_after.contains("▐▛███▜▌"),
+            "logo should NOT appear after alt screen exit (known Claude Code bug), got: {:?}",
+            vt_screen_after
+        );
+
+        // Send /exit to quit
+        send_input(&mut proxy, &sink, b"/exit\r");
+        pump_proxy(&mut proxy, &sink, 1000);
+    }
+}

crates/claude-chill/src/lib.rs

@@ -1,8 +1,13 @@
+#[cfg(test)]
+mod color_preservation_tests;
 pub mod config;
 pub mod escape_filter;
 pub mod escape_sequences;
 pub mod history_filter;
+#[cfg(test)]
+mod integration_tests;
 pub mod key_parser;
 pub mod line_buffer;
 pub mod proxy;
 pub mod redraw_throttler;
+pub mod screen_engine;

crates/claude-chill/src/proxy.rs

@@ -6,6 +6,7 @@ use crate::escape_sequences::{
 };
 use crate::history_filter::HistoryFilter;
 use crate::line_buffer::LineBuffer;
+use crate::screen_engine::ScreenEngine;
 use anyhow::{Context, Result};
 use log::debug;
 use memchr::memmem;
@@ -102,8 +103,7 @@ pub struct Proxy {
     original_termios: Option<Termios>,
     history: LineBuffer,
     history_filter: HistoryFilter,
-    vt_parser: vt100::Parser,
-    vt_prev_screen: Option<vt100::Screen>,
+    screen: ScreenEngine,
     last_output_time: Option<Instant>,
     last_render_time: Option<Instant>,
     last_stdin_time: Option<Instant>,
@@ -270,7 +270,7 @@ impl Proxy {
         let stdout_fd = io::stdout();
         write_all(&stdout_fd, BRACKETED_PASTE_ENABLE)?;
 
-        let vt_parser = vt100::Parser::new(winsize.ws_row, winsize.ws_col, 0);
+        let screen = ScreenEngine::new(winsize.ws_row, winsize.ws_col);
 
         // Seed history with clear screen so replay starts fresh
         let mut history = LineBuffer::new(config.max_history_lines);
@@ -288,8 +288,7 @@ impl Proxy {
             pty_master: pty.master,
             child,
             original_termios: terminal_guard.take(),
-            vt_parser,
-            vt_prev_screen: None,
+            screen,
             last_output_time: None,
             last_render_time: None,
             last_stdin_time: None,
@@ -322,6 +321,109 @@ impl Proxy {
         })
     }
 
+    #[cfg(test)]
+    pub(crate) fn new_for_test(
+        pty_master: OwnedFd,
+        child: Child,
+        config: ProxyConfig,
+        rows: u16,
+        cols: u16,
+    ) -> Self {
+        let screen = ScreenEngine::new(rows, cols);
+        let mut history = LineBuffer::new(config.max_history_lines);
+        history.push_bytes(CLEAR_SCREEN);
+        history.push_bytes(CURSOR_HOME);
+        let auto_lookback_timeout = Duration::from_millis(config.auto_lookback_timeout_ms);
+
+        Self {
+            history,
+            history_filter: HistoryFilter::new(),
+            config,
+            pty_master,
+            child,
+            original_termios: None,
+            screen,
+            last_output_time: None,
+            last_render_time: None,
+            last_stdin_time: None,
+            last_auto_lookback_time: None,
+            auto_lookback_timeout,
+            sync_buffer: Vec::with_capacity(SYNC_BUFFER_CAPACITY),
+            in_sync_block: false,
+            in_lookback_mode: false,
+            in_alternate_screen: false,
+            in_bracketed_paste: false,
+            kitty_mode_supported: false,
+            kitty_mode_stack: 0,
+            kitty_output_parser: TermwizParser::new(),
+            vt_render_pending: false,
+            lookback_cache: Vec::new(),
+            lookback_input_buffer: Vec::with_capacity(INPUT_BUFFER_CAPACITY),
+            output_buffer: Vec::with_capacity(OUTPUT_BUFFER_CAPACITY),
+            sync_start_finder: memmem::Finder::new(SYNC_START),
+            sync_end_finder: memmem::Finder::new(SYNC_END),
+            clear_screen_finder: memmem::Finder::new(CLEAR_SCREEN),
+            cursor_home_finder: memmem::Finder::new(CURSOR_HOME),
+            alt_screen_enter_finder: memmem::Finder::new(ALT_SCREEN_ENTER),
+            alt_screen_exit_finder: memmem::Finder::new(ALT_SCREEN_EXIT),
+            alt_screen_enter_legacy_finder: memmem::Finder::new(ALT_SCREEN_ENTER_LEGACY),
+            alt_screen_exit_legacy_finder: memmem::Finder::new(ALT_SCREEN_EXIT_LEGACY),
+            paste_start_finder: memmem::Finder::new(BRACKETED_PASTE_START),
+            paste_end_finder: memmem::Finder::new(BRACKETED_PASTE_END),
+            pty_drain_buffer: Vec::new(),
+            paste_remainder: Vec::new(),
+        }
+    }
+
+    #[cfg(test)]
+    pub(crate) fn history(&self) -> &LineBuffer {
+        &self.history
+    }
+
+    #[cfg(test)]
+    pub(crate) fn is_in_alternate_screen(&self) -> bool {
+        self.in_alternate_screen
+    }
+
+    #[cfg(test)]
+    pub(crate) fn is_in_bracketed_paste(&self) -> bool {
+        self.in_bracketed_paste
+    }
+
+    #[cfg(test)]
+    pub(crate) fn is_in_sync_block(&self) -> bool {
+        self.in_sync_block
+    }
+
+    #[cfg(test)]
+    pub(crate) fn is_in_lookback_mode(&self) -> bool {
+        self.in_lookback_mode
+    }
+
+    #[cfg(test)]
+    pub(crate) fn vt_screen_text(&mut self) -> String {
+        self.screen.screen_text()
+    }
+
+    #[cfg(test)]
+    pub(crate) fn pty_master_fd_raw(&self) -> i32 {
+        self.pty_master.as_raw_fd()
+    }
+
+    #[cfg(test)]
+    pub(crate) fn force_render<F: AsFd>(&mut self, stdout_fd: &F) -> Result<()> {
+        self.render_vt_screen(stdout_fd)
+    }
+
+    #[cfg(test)]
+    pub(crate) fn flush_drain_buffer<F: AsFd>(&mut self, stdout_fd: &F) -> Result<()> {
+        if !self.pty_drain_buffer.is_empty() {
+            let drained = std::mem::take(&mut self.pty_drain_buffer);
+            self.process_output(&drained, stdout_fd)?;
+        }
+        Ok(())
+    }
+
     pub fn run(&mut self) -> Result<i32> {
         let stdin_fd = io::stdin();
         let stdout_fd = io::stdout();
@@ -406,7 +508,7 @@ impl Proxy {
         self.wait_child()
     }
 
-    fn process_output<F: AsFd>(&mut self, data: &[u8], stdout_fd: &F) -> Result<()> {
+    pub(crate) fn process_output<F: AsFd>(&mut self, data: &[u8], stdout_fd: &F) -> Result<()> {
         self.process_output_inner(data, stdout_fd, true)
     }
 
@@ -428,7 +530,7 @@ impl Proxy {
             // Feed VT but NOT history while in alt screen
             // Alt screen content (TUI editors, etc.) shouldn't be in lookback history
             if feed_vt {
-                self.vt_parser.process(data);
+                self.screen.process(data);
             }
             return self.process_output_alt_screen(data, stdout_fd);
         }
@@ -441,7 +543,7 @@ impl Proxy {
 
         // Feed data to VT emulator (unless already fed by caller)
         if feed_vt {
-            self.vt_parser.process(data);
+            self.screen.process(data);
         }
         self.vt_render_pending = true;
         self.last_output_time = Some(Instant::now());
@@ -517,7 +619,7 @@ impl Proxy {
 
             // Force full VT render to restore main screen content
             debug!("process_output_alt_screen: rendering VT screen after alt exit");
-            self.vt_prev_screen = None;
+            self.screen.force_full_next();
             self.render_vt_screen(stdout_fd)?;
 
             // Data after ALT_EXIT was already fed to VT and history when we processed
@@ -724,32 +826,14 @@ impl Proxy {
     }
 
     fn render_vt_screen<F: AsFd>(&mut self, stdout_fd: &F) -> Result<()> {
-        let is_diff = self.vt_prev_screen.is_some();
+        let body = self.screen.render()?;
         self.output_buffer.clear();
         self.output_buffer.extend_from_slice(SYNC_START);
-
-        match &self.vt_prev_screen {
-            Some(prev) => {
-                // Diff-based render: only send changes
-                self.output_buffer
-                    .extend_from_slice(&self.vt_parser.screen().contents_diff(prev));
-            }
-            None => {
-                // First render: full screen
-                self.output_buffer
-                    .extend_from_slice(&self.vt_parser.screen().contents_formatted());
-            }
-        }
-
-        self.output_buffer
-            .extend_from_slice(&self.vt_parser.screen().cursor_state_formatted());
+        self.output_buffer.extend_from_slice(&body);
         self.output_buffer.extend_from_slice(SYNC_END);
 
-        debug!(
-            "render_vt_screen: diff={} output_len={}\n",
-            is_diff,
-            self.output_buffer.len()
-        );
+        debug!("render_vt_screen: output_len={}", self.output_buffer.len());
+
         // Can't use write_to_terminal here due to borrow checker - can't pass
         // &self.output_buffer while also taking &mut self
         Self::update_kitty_mode_helper(
@@ -760,8 +844,6 @@ impl Proxy {
         );
         write_all(stdout_fd, &self.output_buffer)?;
 
-        // Store current screen for next diff
-        self.vt_prev_screen = Some(self.vt_parser.screen().clone());
         self.vt_render_pending = false;
         self.last_render_time = Some(Instant::now());
         Ok(())
@@ -838,11 +920,11 @@ impl Proxy {
         write_all(stdout_fd, &self.output_buffer)?;
 
         // Force full VT render on next output since terminal now shows history
-        self.vt_prev_screen = None;
+        self.screen.force_full_next();
         Ok(())
     }
 
-    fn process_input<F: AsFd>(&mut self, data: &[u8], stdout_fd: &F) -> Result<()> {
+    pub(crate) fn process_input<F: AsFd>(&mut self, data: &[u8], stdout_fd: &F) -> Result<()> {
         self.last_stdin_time = Some(Instant::now());
 
         debug!(
@@ -1060,7 +1142,7 @@ impl Proxy {
 
         // Force full render since terminal was showing history
         debug!("exit_lookback_mode: rendering VT screen");
-        self.vt_prev_screen = None;
+        self.screen.force_full_next();
         self.render_vt_screen(stdout_fd)?;
 
         Ok(())
@@ -1073,11 +1155,7 @@ impl Proxy {
                 winsize.ws_row, winsize.ws_col
             );
             // Resize VT emulator
-            self.vt_parser
-                .screen_mut()
-                .set_size(winsize.ws_row, winsize.ws_col);
-            // Force full render on next frame since size changed
-            self.vt_prev_screen = None;
+            self.screen.resize(winsize.ws_row, winsize.ws_col);
             // Forward to child process
             unsafe {
                 libc::ioctl(

crates/claude-chill/src/screen_engine.rs

@@ -0,0 +1,264 @@
+//! Screen emulator backed by `wezterm-term`.
+//!
+//! This replaces the previous `vt100` backing. wezterm-term gives us full
+//! modern attribute coverage — OSC 8 hyperlinks, strikethrough, fancy
+//! underline styles, underline color — that vt100 0.16 dropped on render.
+//!
+//! Architecture:
+//!   - `wezterm_term::Terminal` is the byte-driven VT emulator. Feed bytes
+//!     via `advance_bytes`; query state via `screen().visible_lines()`.
+//!   - A `termwiz::surface::Surface` mirrors the last bytes we *emitted*
+//!     downstream; the next render diffs current visible lines against
+//!     this Surface to compute the minimum change set.
+//!   - `termwiz::render::TerminfoRenderer` serializes those Changes into
+//!     bytes using a TrueColor / hyperlink-capable capability set.
+
+use anyhow::Result;
+use std::io::Write;
+use std::sync::Arc;
+use termwiz::caps::{Capabilities, ColorLevel, ProbeHints};
+use termwiz::render::RenderTty;
+use termwiz::render::terminfo::TerminfoRenderer;
+use termwiz::surface::{Change, Position, Surface};
+use wezterm_term::color::ColorPalette;
+use wezterm_term::{Terminal, TerminalConfiguration, TerminalSize};
+
+#[derive(Debug)]
+struct ProxyTermConfig;
+
+impl TerminalConfiguration for ProxyTermConfig {
+    fn color_palette(&self) -> ColorPalette {
+        ColorPalette::default()
+    }
+}
+
+/// `Write + RenderTty` adapter that buffers everything in memory.
+struct CapturedTty {
+    buf: Vec<u8>,
+    cols: usize,
+    rows: usize,
+}
+
+impl Write for CapturedTty {
+    fn write(&mut self, data: &[u8]) -> std::io::Result<usize> {
+        self.buf.extend_from_slice(data);
+        Ok(data.len())
+    }
+
+    fn flush(&mut self) -> std::io::Result<()> {
+        Ok(())
+    }
+}
+
+impl RenderTty for CapturedTty {
+    fn get_size_in_cells(&mut self) -> termwiz::Result<(usize, usize)> {
+        Ok((self.cols, self.rows))
+    }
+}
+
+pub struct ScreenEngine {
+    terminal: Terminal,
+    /// Mirror of what we've *already emitted* downstream. Diffing the
+    /// current terminal screen against this gives us the minimal change
+    /// set to send.
+    mirror: Surface,
+    renderer: TerminfoRenderer,
+    rows: usize,
+    cols: usize,
+    /// When set, the next render emits the full screen instead of a diff.
+    force_full: bool,
+}
+
+impl ScreenEngine {
+    pub fn new(rows: u16, cols: u16) -> Self {
+        let rows = rows as usize;
+        let cols = cols as usize;
+
+        let size = TerminalSize {
+            rows,
+            cols,
+            ..Default::default()
+        };
+        let config: Arc<dyn TerminalConfiguration + Send + Sync> = Arc::new(ProxyTermConfig);
+        // We don't currently surface terminal responses (DA queries, cursor
+        // position reports, etc) back upstream. Matches the previous vt100
+        // behavior, which simply ignored them.
+        let writer: Box<dyn Write + Send> = Box::new(std::io::sink());
+        let terminal = Terminal::new(
+            size,
+            config,
+            "claude-chill",
+            env!("CARGO_PKG_VERSION"),
+            writer,
+        );
+
+        let mirror = Surface::new(cols, rows);
+
+        let caps = Capabilities::new_with_hints(
+            ProbeHints::default()
+                .color_level(Some(ColorLevel::TrueColor))
+                .hyperlinks(Some(true))
+                .bracketed_paste(Some(true)),
+        )
+        .expect("Capabilities::new_with_hints");
+        let renderer = TerminfoRenderer::new(caps);
+
+        Self {
+            terminal,
+            mirror,
+            renderer,
+            rows,
+            cols,
+            force_full: true,
+        }
+    }
+
+    /// Feed bytes from the child pty into the emulator.
+    pub fn process(&mut self, data: &[u8]) {
+        self.terminal.advance_bytes(data);
+    }
+
+    pub fn resize(&mut self, rows: u16, cols: u16) {
+        let rows = rows as usize;
+        let cols = cols as usize;
+        self.terminal.resize(TerminalSize {
+            rows,
+            cols,
+            ..Default::default()
+        });
+        self.mirror.resize(cols, rows);
+        self.rows = rows;
+        self.cols = cols;
+        self.force_full = true;
+    }
+
+    /// Mark the next `render()` call as a full screen redraw rather than a diff.
+    pub fn force_full_next(&mut self) {
+        self.force_full = true;
+    }
+
+    /// Build the change stream needed to bring downstream from `mirror` to
+    /// the current emulator state, encode it as bytes, and update `mirror`.
+    pub fn render(&mut self) -> Result<Vec<u8>> {
+        let lines = {
+            let screen = self.terminal.screen();
+            let rows = self.rows as i64;
+            let start = screen.phys_row(0);
+            let end = screen.phys_row(rows - 1) + 1;
+            screen.lines_in_phys_range(start..end)
+        };
+        let line_refs: Vec<&_> = lines.iter().collect();
+
+        // If forced, reset the mirror so diff_lines emits the full screen.
+        if self.force_full {
+            self.mirror = Surface::new(self.cols, self.rows);
+            self.force_full = false;
+        }
+
+        let mut changes = self.mirror.diff_lines(line_refs);
+
+        // Position the downstream cursor where the emulator's cursor is.
+        let cursor = self.terminal.cursor_pos();
+        let row = cursor.y.max(0) as usize;
+        let col = cursor.x;
+        changes.push(Change::CursorPosition {
+            x: Position::Absolute(col),
+            y: Position::Absolute(row),
+        });
+
+        // Keep the mirror in sync with what we just emitted (minus the final
+        // cursor reposition, which isn't a content change).
+        self.mirror.add_changes(changes.clone());
+
+        let mut tty = CapturedTty {
+            buf: Vec::new(),
+            cols: self.cols,
+            rows: self.rows,
+        };
+        self.renderer
+            .render_to(&changes, &mut tty)
+            .map_err(|e| anyhow::anyhow!("renderer: {}", e))?;
+
+        // Defensive OSC 8 close: TerminfoRenderer only emits the hyperlink
+        // close when transitioning to a non-hyperlinked cell. If our diff
+        // ends inside the hyperlinked region (rest of the row was blank
+        // and didn't need updating), the close is never emitted and the
+        // downstream terminal may keep the hyperlink active across the
+        // boundary. Appending a close here is a no-op when there's no
+        // active hyperlink.
+        tty.buf.extend_from_slice(b"\x1b]8;;\x1b\\");
+
+        Ok(tty.buf)
+    }
+
+    /// Plain-text contents of the visible screen, for tests / lookback.
+    #[cfg(test)]
+    pub fn screen_text(&mut self) -> String {
+        let lines = {
+            let screen = self.terminal.screen();
+            let rows = self.rows as i64;
+            let start = screen.phys_row(0);
+            let end = screen.phys_row(rows - 1) + 1;
+            screen.lines_in_phys_range(start..end)
+        };
+        let mut out = String::new();
+        for (i, line) in lines.iter().enumerate() {
+            if i > 0 {
+                out.push('\n');
+            }
+            out.push_str(&line.as_str());
+        }
+        out
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    fn contains(haystack: &[u8], needle: &[u8]) -> bool {
+        haystack.windows(needle.len()).any(|w| w == needle)
+    }
+
+    fn render(input: &[u8]) -> Vec<u8> {
+        let mut e = ScreenEngine::new(24, 80);
+        e.process(input);
+        e.render().expect("render")
+    }
+
+    #[test]
+    fn osc8_hyperlink_round_trip() {
+        let mut input = Vec::new();
+        input.extend_from_slice(b"\x1b]8;;https://example.com\x1b\\");
+        input.extend_from_slice(b"link");
+        input.extend_from_slice(b"\x1b]8;;\x1b\\");
+        let out = render(&input);
+        assert!(
+            contains(&out, b"\x1b]8;;https://example.com"),
+            "OSC 8 missing in: {:?}",
+            String::from_utf8_lossy(&out)
+        );
+    }
+
+    #[test]
+    fn strikethrough_round_trip() {
+        let out = render(b"\x1b[9mstruck\x1b[0m");
+        assert!(
+            contains(&out, b"[9m") || contains(&out, b";9m"),
+            "SGR 9 missing in: {:?}",
+            String::from_utf8_lossy(&out)
+        );
+    }
+
+    #[test]
+    fn truecolor_round_trip() {
+        let out = render(b"\x1b[38;2;255;128;0morange\x1b[0m");
+        assert!(
+            contains(&out, b"38:2::255:128:0")
+                || contains(&out, b"38;2;255;128;0")
+                || contains(&out, b"38:2:255:128:0"),
+            "truecolor fg missing in: {:?}",
+            String::from_utf8_lossy(&out)
+        );
+    }
+}

crates/pty-mock/Cargo.toml

@@ -0,0 +1,12 @@
+[package]
+name = "pty-mock"
+version.workspace = true
+edition.workspace = true
+authors.workspace = true
+
+[[bin]]
+name = "pty-mock"
+path = "src/bin.rs"
+
+[dependencies]
+clap = { version = "4", features = ["derive"] }

crates/pty-mock/src/bin.rs

@@ -0,0 +1,146 @@
+use clap::{Parser, Subcommand};
+use std::io::{self, BufRead, Read, Write};
+
+#[derive(Parser)]
+struct Cli {
+    #[command(subcommand)]
+    command: Commands,
+}
+
+#[derive(Subcommand)]
+enum Commands {
+    Echo,
+    AltScreen,
+    PasteEcho,
+    BufferFill,
+    SyncBlocks,
+}
+
+fn cmd_echo() {
+    let stdin = io::stdin();
+    let mut stdout = io::stdout();
+    for line in stdin.lock().lines() {
+        let line = match line {
+            Ok(l) => l,
+            Err(_) => break,
+        };
+        if writeln!(stdout, "{}", line).is_err() {
+            break;
+        }
+        if stdout.flush().is_err() {
+            break;
+        }
+    }
+}
+
+fn cmd_alt_screen() {
+    let mut stdout = io::stdout();
+    let mut stdin = io::stdin();
+
+    // Enter alt screen
+    let _ = stdout.write_all(b"\x1b[?1049h");
+    let _ = stdout.flush();
+
+    // Write some content while in alt screen
+    let _ = stdout.write_all(b"alt screen content\r\n");
+    let _ = stdout.flush();
+
+    // Wait for any byte on stdin as trigger to exit
+    let mut trigger = [0u8; 1];
+    let _ = stdin.read_exact(&mut trigger);
+
+    // Exit alt screen
+    let _ = stdout.write_all(b"\x1b[?1049l");
+    let _ = stdout.flush();
+
+    // Write content after alt screen exit
+    let _ = stdout.write_all(b"back to normal\r\n");
+    let _ = stdout.flush();
+}
+
+fn cmd_paste_echo() {
+    let mut stdout = io::stdout();
+    let stdin = io::stdin();
+
+    // Enable bracketed paste mode
+    let _ = stdout.write_all(b"\x1b[?2004h");
+    let _ = stdout.flush();
+
+    // Read lines, prefix paste content
+    for line in stdin.lock().lines() {
+        let line = match line {
+            Ok(l) => l,
+            Err(_) => break,
+        };
+        if writeln!(stdout, "pasted: {}", line).is_err() {
+            break;
+        }
+        if stdout.flush().is_err() {
+            break;
+        }
+    }
+}
+
+fn cmd_buffer_fill() {
+    let mut stdout = io::stdout();
+    let stdin = io::stdin();
+    let mut stdin_lock = stdin.lock();
+
+    // Write large output to fill the PTY buffer
+    let chunk = "X".repeat(1024) + "\r\n";
+    for _ in 0..256 {
+        if stdout.write_all(chunk.as_bytes()).is_err() {
+            break;
+        }
+    }
+    let _ = stdout.flush();
+
+    // Now read stdin and echo it back
+    let mut buf = [0u8; 4096];
+    loop {
+        match stdin_lock.read(&mut buf) {
+            Ok(0) => break,
+            Ok(n) => {
+                if stdout.write_all(&buf[..n]).is_err() {
+                    break;
+                }
+                if stdout.flush().is_err() {
+                    break;
+                }
+            }
+            Err(_) => break,
+        }
+    }
+}
+
+fn cmd_sync_blocks() {
+    let stdin = io::stdin();
+    let mut stdout = io::stdout();
+
+    for line in stdin.lock().lines() {
+        let line = match line {
+            Ok(l) => l,
+            Err(_) => break,
+        };
+        // Wrap response in sync update block
+        let _ = stdout.write_all(b"\x1b[?2026h");
+        if writeln!(stdout, "sync: {}", line).is_err() {
+            break;
+        }
+        let _ = stdout.write_all(b"\x1b[?2026l");
+        if stdout.flush().is_err() {
+            break;
+        }
+    }
+}
+
+fn main() {
+    let cli = Cli::parse();
+    match cli.command {
+        Commands::Echo => cmd_echo(),
+        Commands::AltScreen => cmd_alt_screen(),
+        Commands::PasteEcho => cmd_paste_echo(),
+        Commands::BufferFill => cmd_buffer_fill(),
+        Commands::SyncBlocks => cmd_sync_blocks(),
+    }
+}

flake.nix

@@ -24,6 +24,7 @@
           cargoLock = {
             lockFile = ./Cargo.lock;
           };
+          cargoBuildFlags = [ "-p" "claude-chill" ];
         };
 
       in