Harden alternate screen tracking

src/bin/dosh-client.rs

@@ -6296,6 +6296,60 @@ const FLAG_TRIGGER_LOW_MS: f64 = 50.0;
 /// (covers a sudden latency spike on the very first slow keystroke).
 const GLITCH_FORCE_MS: u128 = 250;
 
+/// Enough recent bytes to join a CSI private-mode sequence split across frames
+/// without retaining arbitrary terminal output.
+const TERMINAL_OUTPUT_PARSE_TAIL: usize = 64;
+
+fn alternate_screen_after_output(mut active: bool, bytes: &[u8]) -> bool {
+    let mut offset = 0usize;
+    while offset < bytes.len() {
+        let Some((next, transition)) = terminal_private_mode_transition(bytes, offset) else {
+            offset += 1;
+            continue;
+        };
+        if let Some(enable) = transition {
+            active = enable;
+        }
+        offset = next.max(offset + 1);
+    }
+    active
+}
+
+fn terminal_private_mode_transition(bytes: &[u8], offset: usize) -> Option<(usize, Option<bool>)> {
+    let mut cursor = offset;
+    match bytes.get(cursor).copied()? {
+        0x1b if bytes.get(cursor + 1) == Some(&b'[') => cursor += 2,
+        0x9b => cursor += 1,
+        _ => return None,
+    }
+
+    if bytes.get(cursor) != Some(&b'?') {
+        return None;
+    }
+    cursor += 1;
+
+    let params_start = cursor;
+    while let Some(byte) = bytes.get(cursor).copied() {
+        match byte {
+            b'0'..=b'9' | b';' | b':' => cursor += 1,
+            b'h' | b'l' => {
+                let params = &bytes[params_start..cursor];
+                let touches_alt = terminal_private_params_include_alt_screen(params);
+                return Some((cursor + 1, touches_alt.then_some(byte == b'h')));
+            }
+            0x40..=0x7e => return Some((cursor + 1, None)),
+            _ => return None,
+        }
+    }
+    None
+}
+
+fn terminal_private_params_include_alt_screen(params: &[u8]) -> bool {
+    params
+        .split(|byte| matches!(byte, b';' | b':'))
+        .any(|param| matches!(param, b"47" | b"1047" | b"1049"))
+}
+
 /// One speculatively-echoed character on the current line.
 #[derive(Clone, Debug)]
 struct PredictedCell {
@@ -6313,6 +6367,9 @@ struct Predictor {
     /// as vim/htop); we never speculate there because we cannot model arbitrary
     /// cursor addressing safely.
     alternate_screen: bool,
+    /// Tail of recent terminal output, retained so alternate-screen transitions
+    /// split across UDP frames are still detected.
+    output_parse_tail: Vec<u8>,
 
     /// Predicted cells for the current line, left-to-right starting at the
     /// column where the cursor sat when this run of predictions began.
@@ -6359,6 +6416,7 @@ impl Predictor {
             mode,
             enabled: enabled && mode != PredictMode::Off,
             alternate_screen: false,
+            output_parse_tail: Vec::new(),
             cells: Vec::new(),
             cursor: 0,
             epoch: 1,
@@ -6381,6 +6439,7 @@ impl Predictor {
         self.epoch += 1;
         self.confirmed_epoch = self.epoch - 1;
         self.alternate_screen = false;
+        self.output_parse_tail.clear();
         self.oldest_pending_at = None;
     }
 
@@ -6537,20 +6596,20 @@ impl Predictor {
     /// and confirms outstanding predictions: a fresh frame means the server has
     /// re-rendered the line, so our speculative glyphs are superseded and erased.
     fn observe_output(&mut self, bytes: &[u8]) {
-        if contains_bytes(bytes, b"\x1b[?1049h")
-            || contains_bytes(bytes, b"\x1b[?1047h")
-            || contains_bytes(bytes, b"\x1b[?47h")
-        {
-            self.alternate_screen = true;
-            let _ = self.discard_all();
-        }
-        if contains_bytes(bytes, b"\x1b[?1049l")
-            || contains_bytes(bytes, b"\x1b[?1047l")
-            || contains_bytes(bytes, b"\x1b[?47l")
-        {
-            self.alternate_screen = false;
+        let mut parse = Vec::with_capacity(self.output_parse_tail.len() + bytes.len());
+        parse.extend_from_slice(&self.output_parse_tail);
+        parse.extend_from_slice(bytes);
+
+        let before = self.alternate_screen;
+        self.alternate_screen = alternate_screen_after_output(self.alternate_screen, &parse);
+        if self.alternate_screen != before {
             let _ = self.discard_all();
         }
+
+        self.output_parse_tail.clear();
+        let keep = parse.len().min(TERMINAL_OUTPUT_PARSE_TAIL);
+        self.output_parse_tail
+            .extend_from_slice(&parse[parse.len().saturating_sub(keep)..]);
     }
 
     /// Sample SRTT from a newly arrived frame and confirm/clear outstanding
@@ -7344,10 +7403,13 @@ const TERMINAL_CLEANUP: &[u8] = concat!(
     "\x1b[?1002l",
     "\x1b[?1001l",
     "\x1b[?1000l",
+    "\x1b[?1004l",
     "\x1b[?1015l",
     "\x1b[?1006l",
     "\x1b[?1005l",
     "\x1b[?2004l",
+    "\x1b[?47l",
+    "\x1b[?1047l",
     "\x1b[?1049l"
 )
 .as_bytes();
@@ -7372,8 +7434,9 @@ mod tests {
         should_hold_during_startup_gate, should_hold_post_submit_input,
         should_repaint_idle_alternate_screen, split_after_command_submit, ssh_destination_host,
         ssh_username, ssh_with_user, startup_command, status_ssh_target, strip_stale_mouse_reports,
-        strip_terminal_focus_reports, toml_bare_key_or_quoted, update_check_requested,
-        update_version_status, upsert_managed_block, valid_forward_host, vscode_safe_alias,
+        strip_terminal_focus_reports, terminal_private_mode_transition, toml_bare_key_or_quoted,
+        update_check_requested, update_version_status, upsert_managed_block, valid_forward_host,
+        vscode_safe_alias,
     };
     use dosh::config::{ClientConfig, CommandExtension, HostConfig};
     use dosh::native::EnvVar;
@@ -7892,6 +7955,61 @@ mod tests {
         assert!(!predictor.alternate_screen);
     }
 
+    #[test]
+    fn predictor_tracks_legacy_and_combined_alternate_screen_modes() {
+        let mut predictor = Predictor::new(true);
+
+        predictor.observe_output(b"\x1b[?1000;1006;1049h");
+        assert!(predictor.alternate_screen);
+
+        predictor.observe_output(b"\x1b[?1006;1000l");
+        assert!(
+            predictor.alternate_screen,
+            "leaving mouse modes must not imply leaving alternate screen"
+        );
+
+        predictor.observe_output(b"\x1b[?1047l");
+        assert!(!predictor.alternate_screen);
+
+        predictor.observe_output(b"\x1b[?47h");
+        assert!(predictor.alternate_screen);
+        predictor.observe_output(b"\x1b[?47l");
+        assert!(!predictor.alternate_screen);
+    }
+
+    #[test]
+    fn predictor_tracks_alternate_screen_split_across_frames() {
+        let mut predictor = Predictor::new(true);
+
+        predictor.observe_output(b"\x1b");
+        assert!(!predictor.alternate_screen);
+        predictor.observe_output(b"[?");
+        assert!(!predictor.alternate_screen);
+        predictor.observe_output(b"10");
+        assert!(!predictor.alternate_screen);
+        predictor.observe_output(b"49h");
+        assert!(predictor.alternate_screen);
+
+        predictor.observe_output(b"\x1b");
+        assert!(predictor.alternate_screen);
+        predictor.observe_output(b"[?104");
+        assert!(predictor.alternate_screen);
+        predictor.observe_output(b"9l");
+        assert!(!predictor.alternate_screen);
+    }
+
+    #[test]
+    fn private_mode_parser_ignores_non_alt_modes() {
+        assert_eq!(
+            terminal_private_mode_transition(b"\x1b[?1000;1006h", 0),
+            Some((13, None))
+        );
+        assert_eq!(
+            terminal_private_mode_transition(b"\x1b[?1000;1049h", 0),
+            Some((13, Some(true)))
+        );
+    }
+
     /// Typing printable characters builds an in-order predicted line and the
     /// local cursor tracks the end of it.
     #[test]