Ignore local screenshot artifacts in repo root

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

.gitignore

@@ -20,3 +20,6 @@ target
 #  option (not recommended) you can uncomment the following to ignore the entire idea folder.
 #.idea/
 .claude
+
+# Local screenshots / scratch artifacts
+/Screenshot*.png

crates/claude-chill/src/color_preservation_tests.rs

@@ -30,18 +30,8 @@ mod tests {
     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()?;
+    fn spawn_echo_child() -> (OwnedFd, Child) {
+        let bin = crate::test_support::pty_mock_binary();
         let pty = openpty(None, None).expect("openpty failed");
 
         let slave_fd = pty.slave.as_raw_fd();
@@ -75,7 +65,7 @@ mod tests {
         let flags = OFlag::from_bits_truncate(flags);
         fcntl(&pty.master, FcntlArg::F_SETFL(flags | OFlag::O_NONBLOCK)).expect("F_SETFL");
 
-        Some((pty.master, child))
+        (pty.master, child)
     }
 
     fn make_proxy(master: OwnedFd, child: Child) -> Proxy {
@@ -106,15 +96,15 @@ mod tests {
 
     /// 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()?;
+    fn render_and_capture(input: &[u8]) -> 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))
+        drain(&rx)
     }
 
     fn contains_bytes(haystack: &[u8], needle: &[u8]) -> bool {
@@ -130,7 +120,7 @@ mod tests {
         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");
+        let captured = render_and_capture(&input);
         assert!(
             contains_bytes(&captured, b"\x1b]8;;https://example.com/foo"),
             "OSC 8 hyperlink open should survive render, got: {:?}",
@@ -147,7 +137,7 @@ mod tests {
     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");
+        let captured = render_and_capture(input);
         assert!(
             contains_bytes(&captured, b"\x1b[9m") || contains_bytes(&captured, b";9m"),
             "SGR 9 strikethrough should survive render, got: {:?}",
@@ -160,7 +150,7 @@ mod tests {
     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");
+        let captured = render_and_capture(input);
         assert!(
             contains_bytes(&captured, b"4:3"),
             "SGR 4:3 curly underline should survive render, got: {:?}",
@@ -173,7 +163,7 @@ mod tests {
     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");
+        let captured = render_and_capture(input);
         assert!(
             contains_bytes(&captured, b"58:2") || contains_bytes(&captured, b"58;2"),
             "SGR 58 underline color should survive render, got: {:?}",
@@ -185,7 +175,7 @@ mod tests {
     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");
+        let captured = render_and_capture(input);
         assert!(
             contains_bytes(&captured, b"\x1b[21m")
                 || contains_bytes(&captured, b";21m")
@@ -202,10 +192,7 @@ mod tests {
     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;
-        };
+        let captured = render_and_capture(input);
         assert!(
             contains_bytes(&captured, b"38;2;255;128;0")
                 || contains_bytes(&captured, b"38:2::255:128:0"),

crates/claude-chill/src/integration_tests.rs

@@ -11,13 +11,8 @@ mod tests {
     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 pty_mock_binary() -> String {
+        crate::test_support::pty_mock_binary()
     }
 
     fn spawn_command(cmd: &str, args: &[&str]) -> (OwnedFd, Child) {
@@ -58,9 +53,8 @@ mod tests {
         (pty.master, child)
     }
 
-    fn spawn_mock(subcommand: &str) -> Option<(OwnedFd, Child)> {
-        let bin = pty_mock_binary()?;
-        Some(spawn_command(&bin, &[subcommand]))
+    fn spawn_mock(subcommand: &str) -> (OwnedFd, Child) {
+        spawn_command(&pty_mock_binary(), &[subcommand])
     }
 
     fn read_pty_output(master: &OwnedFd, timeout_ms: u16) -> Vec<u8> {
@@ -104,9 +98,7 @@ mod tests {
 
     #[test]
     fn test_echo_baseline() {
-        let Some((master, child)) = spawn_mock("echo") else {
-            return;
-        };
+        let (master, child) = spawn_mock("echo");
         let mut proxy = make_proxy(master, child);
         let sink = dev_null();
 
@@ -136,9 +128,7 @@ mod tests {
 
     #[test]
     fn test_alt_screen_tracking() {
-        let Some((master, child)) = spawn_mock("alt-screen") else {
-            return;
-        };
+        let (master, child) = spawn_mock("alt-screen");
         let mut proxy = make_proxy(master, child);
         let sink = dev_null();
 
@@ -178,9 +168,7 @@ mod tests {
 
     #[test]
     fn test_bracketed_paste_flow() {
-        let Some((master, child)) = spawn_mock("paste-echo") else {
-            return;
-        };
+        let (master, child) = spawn_mock("paste-echo");
         let mut proxy = make_proxy(master, child);
         let sink = dev_null();
 
@@ -209,9 +197,7 @@ mod tests {
 
     #[test]
     fn test_split_paste_end_marker() {
-        let Some((master, child)) = spawn_mock("paste-echo") else {
-            return;
-        };
+        let (master, child) = spawn_mock("paste-echo");
         let mut proxy = make_proxy(master, child);
         let sink = dev_null();
 
@@ -252,9 +238,7 @@ mod tests {
 
     #[test]
     fn test_alt_screen_exit_restores_main_content() {
-        let Some((master, child)) = spawn_mock("echo") else {
-            return;
-        };
+        let (master, child) = spawn_mock("echo");
         let mut proxy = make_proxy(master, child);
         let sink = dev_null();
 
@@ -309,9 +293,7 @@ mod tests {
         // 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 (master, child) = spawn_mock("echo");
         let mut proxy = make_proxy(master, child);
         let sink = dev_null();
 
@@ -383,9 +365,7 @@ mod tests {
 
     #[test]
     fn test_sync_block_tracking() {
-        let Some((master, child)) = spawn_mock("echo") else {
-            return;
-        };
+        let (master, child) = spawn_mock("echo");
         let mut proxy = make_proxy(master, child);
         let sink = dev_null();
 
@@ -410,9 +390,7 @@ mod tests {
 
     #[test]
     fn test_lookback_mode_toggle() {
-        let Some((master, child)) = spawn_mock("echo") else {
-            return;
-        };
+        let (master, child) = spawn_mock("echo");
         let mut proxy = make_proxy(master, child);
         let sink = dev_null();
 
@@ -438,6 +416,238 @@ mod tests {
         );
     }
 
+    /// Regression: exiting lookback mode must wipe the visible pane before
+    /// the next VT diff render. Without the explicit CLEAR_SCREEN, blank
+    /// cells in the new screen state can be diffed-as-equal against
+    /// pre-existing characters left over from the lookback dump, leaking
+    /// stale content into the live UI.
+    #[test]
+    fn test_lookback_exit_emits_clear_screen() {
+        use crate::escape_sequences::{CLEAR_SCREEN, CURSOR_HOME, SYNC_START};
+        use nix::unistd::pipe;
+
+        let (master, child) = spawn_mock("echo");
+        let mut proxy = make_proxy(master, child);
+
+        // Capture the proxy's "stdout" so we can inspect what it writes
+        // when exiting lookback mode.
+        let (rx, tx) = pipe().expect("pipe");
+        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");
+
+        // Seed some history so lookback has content to dump.
+        proxy
+            .process_output(b"line 1\r\nline 2\r\nline 3\r\n", &tx)
+            .expect("output");
+
+        // Enter lookback.
+        send_input(&mut proxy, &tx, &[0x1E]);
+        assert!(proxy.is_in_lookback_mode());
+
+        // Drain whatever was emitted up to this point so we only inspect
+        // bytes from the exit path.
+        let mut drain_buf = [0u8; 65536];
+        loop {
+            match nix::unistd::read(rx.as_fd(), &mut drain_buf) {
+                Ok(0) => break,
+                Ok(_) => continue,
+                Err(_) => break,
+            }
+        }
+
+        // Exit lookback. The proxy should write CLEAR_SCREEN + CURSOR_HOME
+        // to wipe the lookback dump before the next VT render.
+        send_input(&mut proxy, &tx, &[0x1E]);
+        assert!(!proxy.is_in_lookback_mode());
+
+        let mut captured = Vec::new();
+        let mut buf = [0u8; 65536];
+        loop {
+            match nix::unistd::read(rx.as_fd(), &mut buf) {
+                Ok(0) => break,
+                Ok(n) => captured.extend_from_slice(&buf[..n]),
+                Err(_) => break,
+            }
+        }
+
+        let clear_pos = captured
+            .windows(CLEAR_SCREEN.len())
+            .position(|w| w == CLEAR_SCREEN);
+        let home_pos = captured
+            .windows(CURSOR_HOME.len())
+            .position(|w| w == CURSOR_HOME);
+        assert!(
+            clear_pos.is_some(),
+            "lookback exit should emit CLEAR_SCREEN, got: {:?}",
+            String::from_utf8_lossy(&captured)
+        );
+        assert!(
+            home_pos.is_some(),
+            "lookback exit should emit CURSOR_HOME, got: {:?}",
+            String::from_utf8_lossy(&captured)
+        );
+
+        // The whole point of the clear is to wipe the lookback dump
+        // *before* the next VT diff repaints. If the repaint went out
+        // first, the diff would have been computed against the live VT
+        // state but landed on a terminal still showing the dump — the
+        // clear that follows would erase the freshly-painted UI. So
+        // assert ordering: CLEAR/HOME come strictly before the repaint
+        // payload (the rendered "line 1" content).
+        // The repaint payload is wrapped by the proxy in BSU/ESU
+        // (SYNC_START / SYNC_END), so its leading byte sequence is a
+        // reliable marker for "where the render starts" — the renderer
+        // itself optimizes "line 1" into "line" + cursor-move + "1",
+        // which makes a literal text search unreliable.
+        let sync_start_pos = captured
+            .windows(SYNC_START.len())
+            .position(|w| w == SYNC_START)
+            .expect("forced repaint should be wrapped in SYNC_START");
+        assert!(
+            clear_pos.unwrap() < sync_start_pos,
+            "CLEAR_SCREEN must precede repaint payload, got clear@{:?} sync@{}",
+            clear_pos,
+            sync_start_pos
+        );
+        assert!(
+            home_pos.unwrap() < sync_start_pos,
+            "CURSOR_HOME must precede repaint payload, got home@{:?} sync@{}",
+            home_pos,
+            sync_start_pos
+        );
+    }
+
+    /// Helper: build a proxy with passthrough_mode enabled and a captured
+    /// stdout pipe. Returns the proxy, the read end of the pipe (rx), and
+    /// the write end (tx) — pass `tx` as the stdout_fd in `process_*`
+    /// calls and read `rx` to inspect what the proxy emitted downstream.
+    fn passthrough_proxy_with_capture() -> (Proxy, OwnedFd, OwnedFd) {
+        use nix::unistd::pipe;
+        let (master, child) = spawn_mock("echo");
+        let mut proxy = make_proxy(master, child);
+        proxy.set_passthrough_mode(true);
+        let (rx, tx) = pipe().expect("pipe");
+        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");
+        (proxy, rx, tx)
+    }
+
+    fn drain_pipe(rx: &OwnedFd) -> Vec<u8> {
+        let mut out = Vec::new();
+        let mut buf = [0u8; 65536];
+        loop {
+            match nix::unistd::read(rx.as_fd(), &mut buf) {
+                Ok(0) => break,
+                Ok(n) => out.extend_from_slice(&buf[..n]),
+                Err(_) => break,
+            }
+        }
+        out
+    }
+
+    /// Core invariant of passthrough mode: bytes from the child PTY land
+    /// on the real terminal byte-for-byte, with no termwiz re-encoding.
+    /// This is what makes claude-chill correct under tmux — tmux sees the
+    /// exact byte stream the child emitted, not a diff'd repaint that can
+    /// drift from tmux's grid.
+    #[test]
+    fn test_passthrough_forwards_bytes_unchanged() {
+        let (mut proxy, rx, tx) = passthrough_proxy_with_capture();
+
+        let input = b"\x1b[31mhello\x1b[0m \x1b]8;;https://x.example\x1b\\link\x1b]8;;\x1b\\\r\n";
+        proxy.process_output(input, &tx).expect("process_output");
+
+        let captured = drain_pipe(&rx);
+        assert_eq!(
+            captured,
+            input,
+            "passthrough must forward bytes verbatim; got {:?} vs {:?}",
+            String::from_utf8_lossy(&captured),
+            String::from_utf8_lossy(input)
+        );
+    }
+
+    /// Passthrough mode skips the deferred-render path entirely so the
+    /// 33ms render loop never fires for steady-state child output.
+    #[test]
+    fn test_passthrough_skips_render_pending() {
+        let (mut proxy, _rx, tx) = passthrough_proxy_with_capture();
+
+        proxy
+            .process_output(b"some output\r\n", &tx)
+            .expect("process_output");
+
+        assert!(
+            !proxy.vt_render_pending(),
+            "passthrough mode must not arm the deferred VT render"
+        );
+    }
+
+    /// State tracking still has to work in passthrough mode — lookback
+    /// (which dumps history then renders a one-shot full repaint) and
+    /// alt-screen detection both depend on wezterm-term's grid being
+    /// kept up to date.
+    #[test]
+    fn test_passthrough_still_feeds_screen_engine() {
+        let (mut proxy, _rx, tx) = passthrough_proxy_with_capture();
+
+        proxy
+            .process_output(b"hello passthrough\r\n", &tx)
+            .expect("process_output");
+
+        let screen = proxy.vt_screen_text();
+        assert!(
+            screen.contains("hello passthrough"),
+            "wezterm-term grid must reflect child output even in \
+             passthrough mode, got: {:?}",
+            screen
+        );
+    }
+
+    /// Alt-screen detection uses byte-pattern matching on the output
+    /// stream, not the VT grid, but we verify the state flips correctly
+    /// in passthrough mode anyway — the alt-screen code path branches on
+    /// `in_alternate_screen` and a missed transition would silently break
+    /// editor handoff.
+    #[test]
+    fn test_passthrough_still_tracks_alt_screen() {
+        use crate::escape_sequences::ALT_SCREEN_ENTER;
+        let (mut proxy, _rx, tx) = passthrough_proxy_with_capture();
+
+        assert!(!proxy.is_in_alternate_screen());
+        proxy
+            .process_output(ALT_SCREEN_ENTER, &tx)
+            .expect("process_output");
+        assert!(
+            proxy.is_in_alternate_screen(),
+            "alt-screen enter detection must work in passthrough mode"
+        );
+    }
+
+    /// Lookback replays the history buffer when the user toggles into
+    /// lookback mode. If passthrough mode skipped history feeding, the
+    /// buffer would be empty on entry and there'd be nothing to replay.
+    #[test]
+    fn test_passthrough_still_records_history() {
+        let (mut proxy, _rx, tx) = passthrough_proxy_with_capture();
+
+        proxy
+            .process_output(b"line for history\r\n", &tx)
+            .expect("process_output");
+
+        let mut history = Vec::new();
+        proxy.history().append_all(&mut history);
+        let s = String::from_utf8_lossy(&history);
+        assert!(
+            s.contains("line for history"),
+            "passthrough mode must still record history for lookback, \
+             got: {:?}",
+            s
+        );
+    }
+
     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);

crates/claude-chill/src/lib.rs

@@ -11,3 +11,5 @@ pub mod line_buffer;
 pub mod proxy;
 pub mod redraw_throttler;
 pub mod screen_engine;
+#[cfg(test)]
+mod test_support;

crates/claude-chill/src/proxy.rs

@@ -93,7 +93,7 @@ impl Drop for TerminalGuard {
     }
 }
 
-const RENDER_DELAY_MS: u64 = 5;
+const RENDER_DELAY_MS: u64 = 33;
 const SYNC_BLOCK_DELAY_MS: u64 = 50;
 
 pub struct Proxy {
@@ -133,6 +133,15 @@ pub struct Proxy {
     paste_end_finder: memmem::Finder<'static>,
     pty_drain_buffer: Vec<u8>,
     paste_remainder: Vec<u8>,
+    /// True when running under tmux ($TMUX is set). In this mode we forward
+    /// child output bytes directly to the terminal instead of differentially
+    /// re-rendering through wezterm-term + termwiz, because tmux is also
+    /// tracking the cell grid and termwiz's `Surface::diff_lines` doesn't
+    /// emit clearing Changes for cells that became blank — the resulting
+    /// stale-cell drift turns into a palimpsest in tmux's view of the pane.
+    /// Lookback (history dump + one-shot full repaint on exit) still uses
+    /// the rendered path; only steady-state output goes raw.
+    passthrough_mode: bool,
 }
 
 /// Returns (supported, initial_flags) - if flags > 0, terminal is already in Kitty mode
@@ -270,6 +279,13 @@ impl Proxy {
         let stdout_fd = io::stdout();
         write_all(&stdout_fd, BRACKETED_PASTE_ENABLE)?;
 
+        // Wipe whatever was on the terminal before we started. The first VT
+        // render is a diff against an empty mirror, which only paints cells
+        // that differ from blank — pre-existing characters that line up with
+        // blank cells in the new render survive as overlap artifacts.
+        write_all(&stdout_fd, CLEAR_SCREEN)?;
+        write_all(&stdout_fd, CURSOR_HOME)?;
+
         let screen = ScreenEngine::new(winsize.ws_row, winsize.ws_col);
 
         // Seed history with clear screen so replay starts fresh
@@ -279,6 +295,11 @@ impl Proxy {
 
         let auto_lookback_timeout = Duration::from_millis(config.auto_lookback_timeout_ms);
 
+        let passthrough_mode = std::env::var_os("TMUX").is_some();
+        if passthrough_mode {
+            debug!("Proxy::spawn: $TMUX detected, enabling passthrough render mode");
+        }
+
         debug!("Proxy::spawn: command={} args={:?}", command, args);
 
         Ok(Self {
@@ -318,6 +339,7 @@ impl Proxy {
             paste_end_finder: memmem::Finder::new(BRACKETED_PASTE_END),
             pty_drain_buffer: Vec::new(),
             paste_remainder: Vec::new(),
+            passthrough_mode,
         })
     }
 
@@ -372,6 +394,7 @@ impl Proxy {
             paste_end_finder: memmem::Finder::new(BRACKETED_PASTE_END),
             pty_drain_buffer: Vec::new(),
             paste_remainder: Vec::new(),
+            passthrough_mode: false,
         }
     }
 
@@ -424,6 +447,16 @@ impl Proxy {
         Ok(())
     }
 
+    #[cfg(test)]
+    pub(crate) fn set_passthrough_mode(&mut self, on: bool) {
+        self.passthrough_mode = on;
+    }
+
+    #[cfg(test)]
+    pub(crate) fn vt_render_pending(&self) -> bool {
+        self.vt_render_pending
+    }
+
     pub fn run(&mut self) -> Result<i32> {
         let stdin_fd = io::stdin();
         let stdout_fd = io::stdout();
@@ -545,7 +578,16 @@ impl Proxy {
         if feed_vt {
             self.screen.process(data);
         }
-        self.vt_render_pending = true;
+        if self.passthrough_mode {
+            // Under tmux: forward bytes raw to the real terminal instead of
+            // queueing a diff render. tmux is the smart emulator and the
+            // termwiz diff path produces palimpsest artifacts in its grid.
+            // The wezterm-term grid is still kept current above so lookback
+            // / one-shot full repaints work.
+            self.write_to_terminal(stdout_fd, data)?;
+        } else {
+            self.vt_render_pending = true;
+        }
         self.last_output_time = Some(Instant::now());
 
         // Process sync blocks for history management
@@ -1140,6 +1182,11 @@ impl Proxy {
 
         self.forward_winsize()?;
 
+        // Clear the lookback dump out of the visible pane so blank cells in
+        // the new VT state don't leak old history through.
+        self.write_to_terminal(stdout_fd, CLEAR_SCREEN)?;
+        self.write_to_terminal(stdout_fd, CURSOR_HOME)?;
+
         // Force full render since terminal was showing history
         debug!("exit_lookback_mode: rendering VT screen");
         self.screen.force_full_next();
@@ -1183,8 +1230,16 @@ impl Proxy {
 
 impl Drop for Proxy {
     fn drop(&mut self) {
-        // Disable bracketed paste before restoring terminal
         let stdout_fd = io::stdout();
+
+        // Reset any attribute state Claude (or claude-chill's renderer)
+        // may have left active so it doesn't leak into the shell prompt.
+        // Don't wipe the screen — once the palimpsest bug is fixed, the
+        // child's final output (e.g. Claude's "Bye!") is fine to leave on
+        // screen, matching how non-TUI CLIs behave at exit.
+        let _ = write_all(&stdout_fd, b"\x1b]8;;\x1b\\");
+        let _ = write_all(&stdout_fd, b"\x1b[0m");
+
         let _ = write_all(&stdout_fd, BRACKETED_PASTE_DISABLE);
 
         if let Some(ref termios) = self.original_termios {

crates/claude-chill/src/screen_engine.rs

@@ -17,12 +17,24 @@ use anyhow::Result;
 use std::io::Write;
 use std::sync::Arc;
 use termwiz::caps::{Capabilities, ColorLevel, ProbeHints};
+use termwiz::cell::CellAttributes;
 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};
 
+fn make_renderer() -> TerminfoRenderer {
+    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");
+    TerminfoRenderer::new(caps)
+}
+
 #[derive(Debug)]
 struct ProxyTermConfig;
 
@@ -93,15 +105,7 @@ impl ScreenEngine {
         );
 
         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);
+        let renderer = make_renderer();
 
         Self {
             terminal,
@@ -150,8 +154,15 @@ impl ScreenEngine {
         let line_refs: Vec<&_> = lines.iter().collect();
 
         // If forced, reset the mirror so diff_lines emits the full screen.
+        // Also recreate the renderer: TerminfoRenderer caches CellAttributes
+        // across render_to calls so it can suppress redundant SGR emission.
+        // When force_full is set the terminal has been mutated out-of-band
+        // (startup, post-resize, alt-screen child output, raw CLEAR_SCREEN
+        // on lookback exit), so the cached attribute state can't be trusted.
+        // Recreate the renderer to start from a known-default pen.
         if self.force_full {
             self.mirror = Surface::new(self.cols, self.rows);
+            self.renderer = make_renderer();
             self.force_full = false;
         }
 
@@ -166,9 +177,14 @@ impl ScreenEngine {
             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());
+        // Reset attributes (and close any active hyperlink) at the end of
+        // the frame, routed through the renderer's state model so its
+        // cached current_attr stays in sync with what we emit. Without
+        // this, a diff that ends inside a styled/linked cell leaves the
+        // renderer thinking those attributes are still active, and the
+        // next render's SGR transitions get computed against the wrong
+        // baseline — manifesting as bg-color smears or sticky links.
+        changes.push(Change::AllAttributes(CellAttributes::default()));
 
         let mut tty = CapturedTty {
             buf: Vec::new(),
@@ -179,14 +195,21 @@ impl ScreenEngine {
             .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.
+        // Advance the mirror only after render_to succeeds. If serialization
+        // fails, the next diff will be computed against a state that
+        // matches what was actually shown — no "assumed emitted" drift.
+        // (CursorPosition / AllAttributes both flow through Surface, so
+        // the mirror's own pen state tracks the renderer's.)
+        self.mirror.add_changes(changes);
+
+        // Belt-and-suspenders wire reset. AllAttributes(default) updates
+        // the renderer's pen, but the renderer is allowed to defer the
+        // actual byte emission until the next cell paint. These raw
+        // sequences guarantee the wire ends each frame at default attrs,
+        // so styles can't leak into any passthrough output that follows
+        // before the next render. They're no-ops when nothing is active.
         tty.buf.extend_from_slice(b"\x1b]8;;\x1b\\");
+        tty.buf.extend_from_slice(b"\x1b[0m");
 
         Ok(tty.buf)
     }
@@ -261,4 +284,106 @@ mod tests {
             String::from_utf8_lossy(&out)
         );
     }
+
+    /// Regression: TerminfoRenderer caches CellAttributes across `render_to`
+    /// calls. We append a raw `\x1b[0m` to the wire after each frame, so on
+    /// the next frame the wire is at default attrs but the renderer's
+    /// cached `current_attr` could disagree if we don't keep them in sync.
+    /// Specifically, a styled run that lands again on the second frame must
+    /// re-emit its SGR — otherwise the renderer suppresses the transition
+    /// (thinking "already active") and the styled text lands unstyled.
+    #[test]
+    fn sgr_reemitted_on_second_frame_after_wire_reset() {
+        let mut e = ScreenEngine::new(24, 80);
+
+        // Frame 1: render red text. Should emit SGR 31 and the trailing
+        // `\x1b[0m` resets the wire.
+        e.process(b"\x1b[31mred\x1b[0m\r\n");
+        let frame1 = e.render().expect("frame1");
+        assert!(
+            contains(&frame1, b"[31m") || contains(&frame1, b";31m"),
+            "frame1 should contain red SGR, got: {:?}",
+            String::from_utf8_lossy(&frame1)
+        );
+        assert!(
+            frame1.ends_with(b"\x1b[0m"),
+            "frame1 should end with SGR 0 to reset the wire"
+        );
+
+        // Frame 2: render different red text on a new line. Renderer's
+        // pen is reset to default by frame1's trailing AllAttributes, so
+        // the SGR 31 must be re-emitted to bring the wire to red again.
+        e.process(b"\x1b[31mmore red\x1b[0m\r\n");
+        let frame2 = e.render().expect("frame2");
+        assert!(
+            contains(&frame2, b"[31m") || contains(&frame2, b";31m"),
+            "frame2 must re-emit red SGR — renderer state drift would \
+             suppress it but the wire was reset, got: {:?}",
+            String::from_utf8_lossy(&frame2)
+        );
+    }
+
+    /// Regression: a hyperlink that's still active on the next frame must
+    /// re-emit the OSC 8 open. The trailing `\x1b]8;;\x1b\\` after each
+    /// frame closes the link on the wire; if we don't keep the renderer's
+    /// model in sync via `Change::AllAttributes(default)`, the renderer
+    /// thinks the link is still active and skips the open on the next frame.
+    #[test]
+    fn hyperlink_reemitted_on_second_frame_after_wire_close() {
+        let mut e = ScreenEngine::new(24, 80);
+
+        let mut link1 = Vec::new();
+        link1.extend_from_slice(b"\x1b]8;;https://a.example\x1b\\");
+        link1.extend_from_slice(b"first\x1b]8;;\x1b\\\r\n");
+        e.process(&link1);
+        let frame1 = e.render().expect("frame1");
+        assert!(
+            contains(&frame1, b"\x1b]8;;https://a.example"),
+            "frame1 should contain hyperlink open"
+        );
+
+        let mut link2 = Vec::new();
+        link2.extend_from_slice(b"\x1b]8;;https://b.example\x1b\\");
+        link2.extend_from_slice(b"second\x1b]8;;\x1b\\\r\n");
+        e.process(&link2);
+        let frame2 = e.render().expect("frame2");
+        assert!(
+            contains(&frame2, b"\x1b]8;;https://b.example"),
+            "frame2 must emit the new hyperlink open — renderer drift \
+             would suppress it after the prior wire close, got: {:?}",
+            String::from_utf8_lossy(&frame2)
+        );
+    }
+
+    /// Regression: when `force_full_next()` fires (lookback exit, alt-screen
+    /// exit, resize), the renderer is recreated so out-of-band terminal
+    /// writes can't leave stale `current_attr`. This test sanity-checks
+    /// that a forced full render after styled content emits a complete
+    /// frame including the SGR — not a "no diff" because the renderer
+    /// thought the style was already on the wire.
+    #[test]
+    fn forced_full_render_reemits_sgr_after_renderer_recreate() {
+        let mut e = ScreenEngine::new(24, 80);
+        e.process(b"\x1b[34mblue text\x1b[0m\r\n");
+        let _ = e.render().expect("frame1");
+
+        // Simulate the proxy path: out-of-band CLEAR_SCREEN was just sent
+        // to the real terminal, and force_full_next was called.
+        e.force_full_next();
+
+        // Render again. Even though no new bytes came in, the forced full
+        // render must emit SGR for the styled cells — they're being
+        // repainted from scratch onto a freshly-cleared terminal.
+        let frame2 = e.render().expect("frame2");
+        assert!(
+            contains(&frame2, b"[34m") || contains(&frame2, b";34m"),
+            "forced full render must re-emit SGR 34 (blue), got: {:?}",
+            String::from_utf8_lossy(&frame2)
+        );
+        assert!(
+            contains(&frame2, b"blue text"),
+            "forced full render must include the cell content, got: {:?}",
+            String::from_utf8_lossy(&frame2)
+        );
+    }
 }

crates/claude-chill/src/test_support.rs

@@ -0,0 +1,44 @@
+//! Shared helpers for `#[cfg(test)]` modules.
+
+use std::path::PathBuf;
+
+/// Locate the `pty-mock` binary built by the workspace.
+///
+/// Honors `CARGO_TARGET_DIR` and falls back to the workspace's `target/`
+/// next to `crates/`. Tries `debug/` first, then `release/`. Panics with
+/// a clear instruction if the binary isn't found — silently skipping
+/// would let CI go green without exercising the PTY-driven coverage that
+/// these tests exist to provide.
+pub fn pty_mock_binary() -> String {
+    let exe_name = if cfg!(windows) {
+        "pty-mock.exe"
+    } else {
+        "pty-mock"
+    };
+
+    let mut candidates: Vec<PathBuf> = Vec::new();
+
+    if let Some(target_dir) = std::env::var_os("CARGO_TARGET_DIR") {
+        let base = PathBuf::from(target_dir);
+        candidates.push(base.join("debug").join(exe_name));
+        candidates.push(base.join("release").join(exe_name));
+    }
+
+    let manifest_dir = PathBuf::from(env!("CARGO_MANIFEST_DIR"));
+    let workspace_target = manifest_dir.join("../../target");
+    candidates.push(workspace_target.join("debug").join(exe_name));
+    candidates.push(workspace_target.join("release").join(exe_name));
+
+    for path in &candidates {
+        if path.exists() {
+            return path.to_string_lossy().into_owned();
+        }
+    }
+
+    panic!(
+        "pty-mock binary not found. Build it first with `cargo build -p pty-mock` \
+         (or set CARGO_TARGET_DIR if you use a non-default target dir). \
+         Searched: {:?}",
+        candidates
+    );
+}