Harden alternate screen tracking

Cargo.lock

@@ -436,7 +436,7 @@ dependencies = [
 
 [[package]]
 name = "dosh"
-version = "1.0.0-rc1"
+version = "1.0.0-rc9"
 dependencies = [
  "anyhow",
  "base64",

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "dosh"
-version = "1.0.0-rc1"
+version = "1.0.0-rc9"
 edition = "2024"
 license = "MIT"
 

scripts/bench-local.sh

@@ -67,6 +67,7 @@ cleanup() {
     kill "$server_pid" 2>/dev/null || true
     wait "$server_pid" 2>/dev/null || true
   fi
+  pkill -f "$server_bin hold --runtime-dir $home/sessions/run" 2>/dev/null || true
   rm -rf "$home"
 }
 trap cleanup EXIT INT TERM
@@ -86,6 +87,7 @@ scrollback = 5000
 auth_ttl_secs = 30
 attach_ticket_ttl_secs = 3600
 allow_attach_tickets = true
+persist_sessions = false
 client_timeout_secs = 60
 retransmit_window = 256
 default_input_mode = "read-write"

src/bin/dosh-client.rs

@@ -36,6 +36,7 @@ use dosh::transport::{
     DoshTransport, SessionEvent, SessionRole, SessionTransportConfig, TransportConfig,
     TransportEvent,
 };
+use dosh::udp::is_transient_udp_send_error;
 use serde::{Deserialize, Serialize};
 use sha2::{Digest, Sha256};
 use std::collections::BTreeMap;
@@ -63,6 +64,10 @@ const STREAM_INITIAL_WINDOW: usize = 1024 * 1024;
 const MAX_PENDING_USER_INPUT_BYTES: usize = 1024 * 1024;
 const STARTUP_INPUT_HOLD: Duration = Duration::from_millis(750);
 const POST_SUBMIT_ALL_INPUT_HOLD: Duration = Duration::from_millis(120);
+const STALE_TERMINAL_INPUT_AFTER: Duration = Duration::from_secs(2);
+const POST_RECONNECT_STALE_INPUT_GRACE: Duration = Duration::from_secs(2);
+const FOCUS_REPAINT_COOLDOWN: Duration = Duration::from_secs(1);
+const ALT_SCREEN_IDLE_REPAINT_AFTER: Duration = Duration::from_secs(15);
 
 /// Sentinel `target_host` the server uses on a server-initiated `StreamOpen` that
 /// represents an SSH-agent connection (rather than a TCP target). The client
@@ -3532,52 +3537,6 @@ async fn send_terminal_udp(socket: &UdpSocket, packet: &[u8], addr: SocketAddr)
     }
 }
 
-fn is_transient_udp_send_error(err: &std::io::Error) -> bool {
-    matches!(
-        err.kind(),
-        std::io::ErrorKind::Interrupted
-            | std::io::ErrorKind::TimedOut
-            | std::io::ErrorKind::WouldBlock
-    ) || err.raw_os_error().is_some_and(is_transient_udp_os_error)
-}
-
-#[cfg(unix)]
-fn is_transient_udp_os_error(code: i32) -> bool {
-    matches!(
-        code,
-        libc::EADDRNOTAVAIL
-            | libc::ECONNREFUSED
-            | libc::ECONNRESET
-            | libc::EHOSTDOWN
-            | libc::EHOSTUNREACH
-            | libc::ENETDOWN
-            | libc::ENETRESET
-            | libc::ENETUNREACH
-            | libc::ETIMEDOUT
-    )
-}
-
-#[cfg(windows)]
-fn is_transient_udp_os_error(code: i32) -> bool {
-    matches!(
-        code,
-        10049  // WSAEADDRNOTAVAIL
-            | 10050 // WSAENETDOWN
-            | 10051 // WSAENETUNREACH
-            | 10052 // WSAENETRESET
-            | 10054 // WSAECONNRESET
-            | 10060 // WSAETIMEDOUT
-            | 10061 // WSAECONNREFUSED
-            | 10064 // WSAEHOSTDOWN
-            | 10065 // WSAEHOSTUNREACH
-    )
-}
-
-#[cfg(not(any(unix, windows)))]
-fn is_transient_udp_os_error(_code: i32) -> bool {
-    false
-}
-
 #[allow(clippy::too_many_arguments)]
 async fn try_native_auth(
     socket: &UdpSocket,
@@ -4376,10 +4335,15 @@ async fn run_terminal(
     let mut pending_user_input_bytes = 0usize;
     let mut startup_input_hold_until: Option<Instant> = None;
     let mut startup_gate_mode = StartupGateMode::HoldControl;
+    let mut stale_terminal_input_suppress_until: Option<Instant> = None;
+    let mut last_terminal_frame_at = Instant::now();
+    let mut last_focus_repaint_at = Instant::now() - FOCUS_REPAINT_COOLDOWN;
+    let mut last_idle_repaint_attempt_at = Instant::now() - ALT_SCREEN_IDLE_REPAINT_AFTER;
     if let Some(frame) = first_frame {
         if !forward_only {
             render_frame(&frame)?;
             predictor.observe_output(&frame.bytes);
+            last_terminal_frame_at = Instant::now();
         }
         if frame.closed {
             return Ok(());
@@ -4433,10 +4397,59 @@ async fn run_terminal(
             biased;
             stdin_msg = stdin_rx.recv() => {
                 match stdin_msg {
-                    Some(bytes) => {
+                    Some(mut bytes) => {
                         if input_matches_escape(&bytes, escape_key.as_deref()) {
                             break;
                         }
+                        let saw_focus_in = input_contains_focus_in(&bytes);
+                        if !forward_only
+                            && saw_focus_in
+                            && last_focus_repaint_at.elapsed() >= FOCUS_REPAINT_COOLDOWN
+                        {
+                            last_focus_repaint_at = Instant::now();
+                            if let Some(frame) = reconnect(
+                                &socket,
+                                &mut cred,
+                                &mut send_seq,
+                                last_size,
+                                &mut frame_buffer,
+                                &mut predictor,
+                            )
+                            .await?
+                            {
+                                refresh_live_addr(&mut addr, &cred)?;
+                                arm_stale_terminal_input_suppression(
+                                    &mut stale_terminal_input_suppress_until,
+                                );
+                                render_frame(&frame)?;
+                                predictor.observe_output(&frame.bytes);
+                                last_terminal_frame_at = Instant::now();
+                                last_packet_at = Instant::now();
+                                flush_pending_user_input(
+                                    &socket,
+                                    addr,
+                                    &cred,
+                                    &mut send_seq,
+                                    &mut predictor,
+                                    &mut pending_user_input,
+                                    &mut pending_user_input_bytes,
+                                )
+                                .await?;
+                            }
+                        }
+                        bytes = strip_terminal_focus_reports(&bytes);
+                        if bytes.is_empty() {
+                            continue;
+                        }
+                        if should_strip_stale_terminal_reports(
+                            last_packet_at.elapsed(),
+                            stale_terminal_input_suppress_until,
+                        ) {
+                            bytes = strip_stale_mouse_reports(&bytes);
+                            if bytes.is_empty() {
+                                continue;
+                            }
+                        }
                         if cred.mode != "view-only" && cred.mode != "forward-only" {
                             if let Some(deadline) = startup_input_hold_until {
                                 if !predictor.alternate_screen
@@ -4535,9 +4548,13 @@ async fn run_terminal(
                                 .await?
                                 {
                                     refresh_live_addr(&mut addr, &cred)?;
+                                    arm_stale_terminal_input_suppression(
+                                        &mut stale_terminal_input_suppress_until,
+                                    );
                                     if !forward_only {
                                         render_frame(&frame)?;
                                         predictor.observe_output(&frame.bytes);
+                                        last_terminal_frame_at = Instant::now();
                                     }
                                     last_packet_at = Instant::now();
                                     flush_pending_user_input(
@@ -4594,9 +4611,13 @@ async fn run_terminal(
                     .await?
                 {
                     refresh_live_addr(&mut addr, &cred)?;
+                    arm_stale_terminal_input_suppression(
+                        &mut stale_terminal_input_suppress_until,
+                    );
                     if !forward_only {
                         render_frame(&frame)?;
                         predictor.observe_output(&frame.bytes);
+                        last_terminal_frame_at = Instant::now();
                     }
                     last_packet_at = Instant::now();
                     flush_pending_user_input(
@@ -4644,9 +4665,13 @@ async fn run_terminal(
                             .await?
                             {
                                 refresh_live_addr(&mut addr, &cred)?;
+                                arm_stale_terminal_input_suppression(
+                                    &mut stale_terminal_input_suppress_until,
+                                );
                                 if !forward_only {
                                     render_frame(&frame)?;
                                     predictor.observe_output(&frame.bytes);
+                                    last_terminal_frame_at = Instant::now();
                                 }
                                 last_packet_at = Instant::now();
                                 flush_pending_user_input(
@@ -4672,6 +4697,7 @@ async fn run_terminal(
                             if !forward_only {
                                 render_frame(&frame)?;
                                 predictor.observe_output(&frame.bytes);
+                                last_terminal_frame_at = Instant::now();
                                 flush_startup_input_if_ready(
                                     &socket,
                                     addr,
@@ -4765,9 +4791,13 @@ async fn run_terminal(
                             .await?
                             {
                                 refresh_live_addr(&mut addr, &cred)?;
+                                arm_stale_terminal_input_suppression(
+                                    &mut stale_terminal_input_suppress_until,
+                                );
                                 if !forward_only {
                                     render_frame(&frame)?;
                                     predictor.observe_output(&frame.bytes);
+                                    last_terminal_frame_at = Instant::now();
                                 }
                                 last_packet_at = Instant::now();
                                 flush_pending_user_input(
@@ -5157,9 +5187,13 @@ async fn run_terminal(
                     .await?
                     {
                         refresh_live_addr(&mut addr, &cred)?;
+                        arm_stale_terminal_input_suppression(
+                            &mut stale_terminal_input_suppress_until,
+                        );
                         if !forward_only {
                             render_frame(&frame)?;
                             predictor.observe_output(&frame.bytes);
+                            last_terminal_frame_at = Instant::now();
                         }
                         last_packet_at = Instant::now();
                         flush_pending_user_input(
@@ -5201,6 +5235,44 @@ async fn run_terminal(
                         (&mut startup_input_hold_until, &mut startup_gate_mode),
                     )
                     .await?;
+                    let now = Instant::now();
+                    if should_repaint_idle_alternate_screen(
+                        predictor.alternate_screen,
+                        last_terminal_frame_at,
+                        last_idle_repaint_attempt_at,
+                        now,
+                    ) {
+                        last_idle_repaint_attempt_at = now;
+                        if let Some(frame) = reconnect(
+                            &socket,
+                            &mut cred,
+                            &mut send_seq,
+                            last_size,
+                            &mut frame_buffer,
+                            &mut predictor,
+                        )
+                        .await?
+                        {
+                            refresh_live_addr(&mut addr, &cred)?;
+                            arm_stale_terminal_input_suppression(
+                                &mut stale_terminal_input_suppress_until,
+                            );
+                            render_frame(&frame)?;
+                            predictor.observe_output(&frame.bytes);
+                            last_terminal_frame_at = Instant::now();
+                            last_packet_at = Instant::now();
+                            flush_pending_user_input(
+                                &socket,
+                                addr,
+                                &cred,
+                                &mut send_seq,
+                                &mut predictor,
+                                &mut pending_user_input,
+                                &mut pending_user_input_bytes,
+                            )
+                            .await?;
+                        }
+                    }
                 }
                 // Refresh / clear the non-destructive disconnect status line based
                 // on how long the link has been silent (recomputed after any
@@ -5562,6 +5634,53 @@ fn should_flush_terminal_input_after_contact(
     !forward_only && !pending_empty && mode != "view-only" && mode != "forward-only"
 }
 
+fn should_strip_stale_terminal_reports(
+    silent_for: Duration,
+    suppress_until: Option<Instant>,
+) -> bool {
+    silent_for >= STALE_TERMINAL_INPUT_AFTER
+        || suppress_until.is_some_and(|deadline| Instant::now() < deadline)
+}
+
+fn input_contains_focus_in(bytes: &[u8]) -> bool {
+    contains_bytes(bytes, b"\x1b[I") || contains_bytes(bytes, b"\x9bI")
+}
+
+fn strip_terminal_focus_reports(bytes: &[u8]) -> Vec<u8> {
+    let mut out = Vec::with_capacity(bytes.len());
+    let mut offset = 0;
+    while offset < bytes.len() {
+        match bytes.get(offset..) {
+            Some([0x1b, b'[', b'I' | b'O', ..]) => {
+                offset += 3;
+            }
+            Some([0x9b, b'I' | b'O', ..]) => {
+                offset += 2;
+            }
+            _ => {
+                out.push(bytes[offset]);
+                offset += 1;
+            }
+        }
+    }
+    out
+}
+
+fn should_repaint_idle_alternate_screen(
+    alternate_screen: bool,
+    last_terminal_frame_at: Instant,
+    last_attempt_at: Instant,
+    now: Instant,
+) -> bool {
+    alternate_screen
+        && now.duration_since(last_terminal_frame_at) >= ALT_SCREEN_IDLE_REPAINT_AFTER
+        && now.duration_since(last_attempt_at) >= ALT_SCREEN_IDLE_REPAINT_AFTER
+}
+
+fn arm_stale_terminal_input_suppression(suppress_until: &mut Option<Instant>) {
+    *suppress_until = Some(Instant::now() + POST_RECONNECT_STALE_INPUT_GRACE);
+}
+
 async fn flush_pending_user_input(
     socket: &UdpSocket,
     addr: SocketAddr,
@@ -5623,6 +5742,7 @@ fn stale_mouse_report_len(bytes: &[u8], offset: usize) -> Option<usize> {
     match bytes.get(offset).copied()? {
         0x1b if bytes.get(offset + 1) == Some(&b'[') => match bytes.get(offset + 2).copied() {
             Some(b'M') if offset + 6 <= bytes.len() => Some(6),
+            Some(b'I' | b'O') => Some(3),
             Some(b'<') => mouse_report_params_len(bytes, offset + 3, 2).map(|len| len + 3),
             Some(byte) if byte.is_ascii_digit() => {
                 mouse_report_params_len(bytes, offset + 2, 2).map(|len| len + 2)
@@ -5631,13 +5751,15 @@ fn stale_mouse_report_len(bytes: &[u8], offset: usize) -> Option<usize> {
         },
         0x9b => match bytes.get(offset + 1).copied() {
             Some(b'M') if offset + 5 <= bytes.len() => Some(5),
+            Some(b'I' | b'O') => Some(2),
             Some(b'<') => mouse_report_params_len(bytes, offset + 2, 2).map(|len| len + 2),
             Some(byte) if byte.is_ascii_digit() => {
                 mouse_report_params_len(bytes, offset + 1, 2).map(|len| len + 1)
             }
             _ => None,
         },
-        byte if byte.is_ascii_digit() => mouse_report_params_len(bytes, offset, 1),
+        byte if byte.is_ascii_digit() => mouse_report_params_len(bytes, offset, 1)
+            .or_else(|| orphan_mouse_suffix_len(bytes, offset)),
         _ => None,
     }
 }
@@ -5659,6 +5781,21 @@ fn mouse_report_params_len(bytes: &[u8], offset: usize, min_semicolons: usize) -
     None
 }
 
+fn orphan_mouse_suffix_len(bytes: &[u8], offset: usize) -> Option<usize> {
+    if offset != 0 {
+        return None;
+    }
+    let mut cursor = offset;
+    while let Some(byte) = bytes.get(cursor).copied() {
+        match byte {
+            b'0'..=b'9' => cursor += 1,
+            b'M' | b'm' if cursor > offset => return Some(cursor + 1 - offset),
+            _ => return None,
+        }
+    }
+    None
+}
+
 fn stale_mouse_report_maybe_incomplete(bytes: &[u8], offset: usize) -> bool {
     let Some(rest) = bytes.get(offset..) else {
         return false;
@@ -5667,19 +5804,21 @@ fn stale_mouse_report_maybe_incomplete(bytes: &[u8], offset: usize) -> bool {
         [0x1b] | [0x1b, b'['] | [0x1b, b'[', b'<'] => true,
         [0x1b, b'[', b'M', ..] if rest.len() < 6 => true,
         [0x1b, b'[', b'<', params @ ..] | [0x1b, b'[', params @ ..]
-            if params_are_mouse_prefix(params) =>
+            if params_are_mouse_prefix(params, 2) =>
         {
             true
         }
         [0x9b] | [0x9b, b'<'] => true,
         [0x9b, b'M', ..] if rest.len() < 5 => true,
-        [0x9b, b'<', params @ ..] | [0x9b, params @ ..] if params_are_mouse_prefix(params) => true,
-        params if params_are_mouse_prefix(params) => true,
+        [0x9b, b'<', params @ ..] | [0x9b, params @ ..] if params_are_mouse_prefix(params, 2) => {
+            true
+        }
+        params if params_are_mouse_prefix(params, 2) => true,
         _ => false,
     }
 }
 
-fn params_are_mouse_prefix(params: &[u8]) -> bool {
+fn params_are_mouse_prefix(params: &[u8], min_semicolons: usize) -> bool {
     let mut semicolons = 0usize;
     let mut saw_digit = false;
     for byte in params {
@@ -5689,7 +5828,7 @@ fn params_are_mouse_prefix(params: &[u8]) -> bool {
             _ => return false,
         }
     }
-    saw_digit && semicolons >= 1
+    saw_digit && semicolons >= min_semicolons
 }
 
 async fn flush_startup_input_if_ready(
@@ -6157,6 +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 {
@@ -6174,6 +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.
@@ -6220,6 +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,
@@ -6242,6 +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;
     }
 
@@ -6398,20 +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
@@ -7205,10 +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();
@@ -7216,32 +7417,35 @@ const TERMINAL_CLEANUP: &[u8] = concat!(
 #[cfg(test)]
 mod tests {
     use super::{
-        CachedCredential, DisconnectStatus, DynamicForward, FRAME_GAP_RESYNC_AFTER_MS, FrameBuffer,
-        LocalForward, MAX_PENDING_USER_INPUT_BYTES, POST_SUBMIT_ALL_INPUT_HOLD, PendingStreamOpen,
-        PredictMode, Predictor, RESTART_STATUS_SCRIPT, RemoteForward, STARTUP_INPUT_HOLD,
-        SshConfig, StartupGateMode, StatusAction, auth_allows, cache_key, cache_server_prefix,
-        clear_cached_credentials, ensure_tui_safe_status_overlay, input_matches_escape,
-        is_local_status_target, is_resume_response_for_client, is_transient_udp_os_error,
-        latest_release_download_url, load_first_native_identity_with_prompt, parse_dynamic_forward,
-        parse_escape_key, parse_local_forward, parse_remote_forward, parse_ssh_config,
-        post_submit_hold_duration, queue_pending_user_input, raw_contains_host_table,
-        recv_response_until, refresh_live_addr, release_tag_download_url,
-        release_tag_from_effective_url, release_version_from_tag, render_status_clear,
-        render_status_overlay, requested_env, resolved_startup_command, retransmit_stream_opens,
-        rewrite_forward_command, selected_predict_mode, selected_udp_host, server_version_mismatch,
-        should_flush_terminal_input_after_contact, should_hold_during_startup_gate,
-        should_hold_post_submit_input, split_after_command_submit, ssh_destination_host,
+        ALT_SCREEN_IDLE_REPAINT_AFTER, CachedCredential, DisconnectStatus, DynamicForward,
+        FRAME_GAP_RESYNC_AFTER_MS, FrameBuffer, LocalForward, MAX_PENDING_USER_INPUT_BYTES,
+        POST_SUBMIT_ALL_INPUT_HOLD, PendingStreamOpen, PredictMode, Predictor,
+        RESTART_STATUS_SCRIPT, RemoteForward, STARTUP_INPUT_HOLD, SshConfig, StartupGateMode,
+        StatusAction, auth_allows, cache_key, cache_server_prefix, clear_cached_credentials,
+        ensure_tui_safe_status_overlay, input_contains_focus_in, input_matches_escape,
+        is_local_status_target, is_resume_response_for_client, latest_release_download_url,
+        load_first_native_identity_with_prompt, parse_dynamic_forward, parse_escape_key,
+        parse_local_forward, parse_remote_forward, parse_ssh_config, post_submit_hold_duration,
+        queue_pending_user_input, raw_contains_host_table, recv_response_until, refresh_live_addr,
+        release_tag_download_url, release_tag_from_effective_url, release_version_from_tag,
+        render_status_clear, render_status_overlay, requested_env, resolved_startup_command,
+        retransmit_stream_opens, rewrite_forward_command, selected_predict_mode, selected_udp_host,
+        server_version_mismatch, should_flush_terminal_input_after_contact,
+        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,
-        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;
     use dosh::protocol::{self, Frame, PacketKind};
+    use dosh::udp::is_transient_udp_send_error;
     use ed25519_dalek::{SigningKey, VerifyingKey};
     use std::collections::{HashMap, VecDeque};
     use std::fs;
-    use std::time::Duration;
+    use std::time::{Duration, Instant};
 
     fn test_args(server: &str, command: &[&str]) -> super::Args {
         super::Args {
@@ -7751,6 +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]
@@ -8467,18 +8726,34 @@ mod tests {
     fn transient_udp_send_errors_are_not_terminal_fatal() {
         #[cfg(unix)]
         {
-            assert!(is_transient_udp_os_error(libc::ENETUNREACH));
-            assert!(is_transient_udp_os_error(libc::EHOSTUNREACH));
-            assert!(is_transient_udp_os_error(libc::EADDRNOTAVAIL));
-            assert!(!is_transient_udp_os_error(libc::EINVAL));
+            assert!(is_transient_udp_send_error(
+                &std::io::Error::from_raw_os_error(libc::ENETUNREACH)
+            ));
+            assert!(is_transient_udp_send_error(
+                &std::io::Error::from_raw_os_error(libc::EHOSTUNREACH)
+            ));
+            assert!(is_transient_udp_send_error(
+                &std::io::Error::from_raw_os_error(libc::EADDRNOTAVAIL)
+            ));
+            assert!(!is_transient_udp_send_error(
+                &std::io::Error::from_raw_os_error(libc::EINVAL)
+            ));
         }
 
         #[cfg(windows)]
         {
-            assert!(is_transient_udp_os_error(10051)); // WSAENETUNREACH
-            assert!(is_transient_udp_os_error(10065)); // WSAEHOSTUNREACH
-            assert!(is_transient_udp_os_error(10049)); // WSAEADDRNOTAVAIL
-            assert!(!is_transient_udp_os_error(10022)); // WSAEINVAL
+            assert!(is_transient_udp_send_error(
+                &std::io::Error::from_raw_os_error(10051)
+            )); // WSAENETUNREACH
+            assert!(is_transient_udp_send_error(
+                &std::io::Error::from_raw_os_error(10065)
+            )); // WSAEHOSTUNREACH
+            assert!(is_transient_udp_send_error(
+                &std::io::Error::from_raw_os_error(10049)
+            )); // WSAEADDRNOTAVAIL
+            assert!(!is_transient_udp_send_error(
+                &std::io::Error::from_raw_os_error(10022)
+            )); // WSAEINVAL
         }
     }
 
@@ -8495,6 +8770,70 @@ mod tests {
         assert_eq!(strip_stale_mouse_reports(b"152;1Mls\r"), b"ls\r");
     }
 
+    #[test]
+    fn split_stale_mouse_suffixes_are_stripped_from_pending_input() {
+        assert_eq!(strip_stale_mouse_reports(b"1M35;149;1Mls\r"), b"ls\r");
+        assert_eq!(strip_stale_mouse_reports(b"10m"), b"");
+    }
+
+    #[test]
+    fn numeric_semicolon_input_survives_stale_filter() {
+        assert_eq!(strip_stale_mouse_reports(b"123;"), b"123;");
+        assert_eq!(strip_stale_mouse_reports(b"12;34"), b"12;34");
+        assert_eq!(strip_stale_mouse_reports(b"echo 1;"), b"echo 1;");
+    }
+
+    #[test]
+    fn incomplete_three_field_mouse_prefix_is_suppressed() {
+        assert_eq!(strip_stale_mouse_reports(b"35;152;"), b"");
+        assert_eq!(strip_stale_mouse_reports(b"\x1b[<35;152;"), b"");
+        assert_eq!(strip_stale_mouse_reports(b"\x9b35;152;"), b"");
+    }
+
+    #[test]
+    fn stale_focus_reports_are_stripped_from_pending_input() {
+        assert_eq!(strip_stale_mouse_reports(b"\x1b[Ihello\x1b[O"), b"hello");
+        assert_eq!(strip_stale_mouse_reports(b"\x9bIhello\x9bO"), b"hello");
+    }
+
+    #[test]
+    fn focus_in_reports_trigger_local_repaint_detection() {
+        assert!(input_contains_focus_in(b"\x1b[I"));
+        assert!(input_contains_focus_in(b"before\x9bIafter"));
+        assert!(!input_contains_focus_in(b"\x1b[O"));
+        assert!(!input_contains_focus_in(b"\x1b[A"));
+    }
+
+    #[test]
+    fn focus_reports_are_never_forwarded_as_user_input() {
+        assert_eq!(strip_terminal_focus_reports(b"\x1b[Ihello\x1b[O"), b"hello");
+        assert_eq!(strip_terminal_focus_reports(b"\x9bIhello\x9bO"), b"hello");
+        assert_eq!(strip_terminal_focus_reports(b"\x1b[A"), b"\x1b[A");
+        assert_eq!(
+            strip_terminal_focus_reports(b"before\x1b[Iafter"),
+            b"beforeafter"
+        );
+    }
+
+    #[test]
+    fn idle_repaint_only_runs_for_stale_alternate_screen() {
+        let now = Instant::now();
+        let stale = now - ALT_SCREEN_IDLE_REPAINT_AFTER - Duration::from_secs(1);
+        let recent = now - Duration::from_secs(1);
+        assert!(should_repaint_idle_alternate_screen(
+            true, stale, stale, now
+        ));
+        assert!(!should_repaint_idle_alternate_screen(
+            false, stale, stale, now
+        ));
+        assert!(!should_repaint_idle_alternate_screen(
+            true, recent, stale, now
+        ));
+        assert!(!should_repaint_idle_alternate_screen(
+            true, stale, recent, now
+        ));
+    }
+
     #[test]
     fn non_mouse_escape_input_survives_stale_filter() {
         assert_eq!(strip_stale_mouse_reports(b"\x1b[A"), b"\x1b[A");

src/bin/dosh-server.rs

@@ -28,6 +28,7 @@ use dosh::protocol::{
     TicketAttachBody, TicketAttachEnvelope, TicketAttachOkEnvelope,
 };
 use dosh::pty::{PtyHandle, PtyOutput, adopt_pty_from_fd, spawn_pty_session};
+use dosh::udp::is_transient_udp_send_error;
 use sha2::{Digest, Sha256};
 use std::collections::{BTreeMap, HashMap, HashSet, VecDeque};
 use std::fs;
@@ -51,6 +52,7 @@ const STREAM_INITIAL_WINDOW: usize = 1024 * 1024;
 /// have accumulated since the last mirror. Keeps the atomic write off the
 /// per-packet hot path while bounding how much fresh output a crash can lose.
 const SCREEN_PERSIST_BYTES: usize = 4096;
+const IMPLICIT_EMPTY_SESSION_GRACE_SECS: u64 = 300;
 
 /// Sentinel `target_host` sent to the client on a server-initiated `StreamOpen`
 /// that carries an SSH-agent connection (the client splices it into its local
@@ -432,6 +434,7 @@ struct PendingStreamOpen {
     attempts: u32,
 }
 
+#[derive(Clone)]
 struct PendingNativeAuth {
     client: dosh::native::NativeClientHello,
     server: NativeServerHello,
@@ -510,15 +513,16 @@ impl ServerState {
         Ok(())
     }
 
-    /// Whether a session named `name` should be backed by a persistent holder.
+    /// Whether a session should be backed by a persistent holder.
     ///
-    /// With persistence enabled, explicitly named sessions get a detached
-    /// holder. Implicit `term-<millis>-<pid>` sessions are one-off terminals
-    /// created by `dosh host`; users cannot intentionally reattach to them by
-    /// name, so persisting them only leaves stale holders that can be
-    /// accidentally re-adopted after restarts.
-    fn should_persist_session(&self, name: &str) -> bool {
-        self.config.persist_sessions && !protocol::is_implicit_session_name(name)
+    /// With persistence enabled, every interactive session gets a detached holder
+    /// so an update/restart of `dosh-server` behaves like a transient network
+    /// break. Named sessions can sit empty for the normal client timeout.
+    /// Generated one-off sessions are also persisted, but cleanup gives them a
+    /// shorter empty grace period so invisible abandoned holders do not linger
+    /// indefinitely.
+    fn should_persist_session(&self, _name: &str) -> bool {
+        self.config.persist_sessions
     }
 
     /// Spawn (or, in the persistent case, spawn-and-adopt) a PTY for a session.
@@ -606,20 +610,6 @@ impl ServerState {
             if self.sessions.contains_key(&name) {
                 continue;
             }
-            if !self.should_persist_session(&name) {
-                eprintln!(
-                    "discarding stale implicit persistent session {name} (shell pid {})",
-                    meta.shell_pid
-                );
-                persist::request_shutdown(&sessions_dir, &name, None);
-                if meta.shell_pid > 0 {
-                    let _ = unsafe { libc::kill(meta.shell_pid, libc::SIGHUP) };
-                    let _ = unsafe { libc::kill(meta.shell_pid, libc::SIGTERM) };
-                    std::thread::sleep(Duration::from_millis(50));
-                    let _ = unsafe { libc::kill(meta.shell_pid, libc::SIGKILL) };
-                }
-                continue;
-            }
             let (pty, control) = match self.adopt_persistent_pty(&name) {
                 Ok(pair) => pair,
                 Err(err) => {
@@ -669,6 +659,7 @@ impl ServerState {
     fn insert_client(&mut self, session_name: &str, client_id: [u8; 16], client: ClientState) {
         if let Some(session) = self.sessions.get_mut(session_name) {
             session.clients.insert(client_id, client);
+            session.empty_since = None;
             self.client_index
                 .insert(client_id, session_name.to_string());
         }
@@ -863,6 +854,7 @@ async fn handle_packet(
         | PacketKind::StreamEof
         | PacketKind::StreamWindowAdjust
         | PacketKind::RekeyAck
+        | PacketKind::Detach
             if find_client_decrypt_key(state, &packet.header).is_err() =>
         {
             send_reject_to_client(socket, peer, packet.header.conn_id, "unknown client").await
@@ -980,7 +972,7 @@ async fn handle_native_client_hello(
     };
     let body = protocol::to_body(&NativeServerHelloBody { hello })?;
     let out = protocol::encode_plain(PacketKind::NativeServerHello, pending_id, 1, 0, &body)?;
-    socket.send_to(&out, peer).await?;
+    let _ = send_udp(socket, &out, peer).await?;
     Ok(())
 }
 
@@ -991,8 +983,8 @@ async fn handle_native_user_auth(
     packet: &protocol::Packet,
 ) -> Result<()> {
     let pending = {
-        let mut locked = state.lock().expect("server state poisoned");
-        locked.pending_native.remove(&packet.header.conn_id)
+        let locked = state.lock().expect("server state poisoned");
+        locked.pending_native.get(&packet.header.conn_id).cloned()
     };
     let Some(pending) = pending else {
         return send_reject_to_client(socket, peer, packet.header.conn_id, "unknown native auth")
@@ -1008,11 +1000,38 @@ async fn handle_native_user_auth(
         .await;
     }
     if pending.created_at.elapsed() > Duration::from_secs(30) {
+        state
+            .lock()
+            .expect("server state poisoned")
+            .pending_native
+            .remove(&packet.header.conn_id);
         return send_reject_to_client(socket, peer, packet.header.conn_id, "native auth expired")
             .await;
     }
-    let body = protocol::decrypt_body(packet, &pending.session_key, CLIENT_TO_SERVER)?;
-    let req: NativeUserAuthBody = protocol::from_body(&body)?;
+    let body = match protocol::decrypt_body(packet, &pending.session_key, CLIENT_TO_SERVER) {
+        Ok(body) => body,
+        Err(_) => {
+            return send_reject_to_client(
+                socket,
+                peer,
+                packet.header.conn_id,
+                "native auth decrypt failed",
+            )
+            .await;
+        }
+    };
+    let req: NativeUserAuthBody = match protocol::from_body(&body) {
+        Ok(req) => req,
+        Err(_) => {
+            return send_reject_to_client(
+                socket,
+                peer,
+                packet.header.conn_id,
+                "invalid native auth body",
+            )
+            .await;
+        }
+    };
     if pending.client.requested_mode == "doctor" {
         let check_result = {
             let locked = state.lock().expect("server state poisoned");
@@ -1048,6 +1067,11 @@ async fn handle_native_user_auth(
                 .await;
             }
         };
+        state
+            .lock()
+            .expect("server state poisoned")
+            .pending_native
+            .remove(&packet.header.conn_id);
         let body = protocol::to_body(&check)?;
         let out = protocol::encode_encrypted(
             PacketKind::NativeAuthCheckOk,
@@ -1058,7 +1082,7 @@ async fn handle_native_user_auth(
             SERVER_TO_CLIENT,
             &body,
         )?;
-        socket.send_to(&out, peer).await?;
+        let _ = send_udp(socket, &out, peer).await?;
         return Ok(());
     }
 
@@ -1228,6 +1252,11 @@ async fn handle_native_user_auth(
     if let Some((listener, path)) = agent_listener {
         spawn_agent_forward(state, socket, client_id, listener, path);
     }
+    state
+        .lock()
+        .expect("server state poisoned")
+        .pending_native
+        .remove(&packet.header.conn_id);
 
     let ok = NativeAuthOk {
         client_id,
@@ -1251,7 +1280,7 @@ async fn handle_native_user_auth(
         SERVER_TO_CLIENT,
         &body,
     )?;
-    socket.send_to(&out, peer).await?;
+    let _ = send_udp(socket, &out, peer).await?;
     Ok(())
 }
 
@@ -1359,7 +1388,7 @@ async fn handle_bootstrap_attach(
         SERVER_TO_CLIENT,
         &body,
     )?;
-    socket.send_to(&out, peer).await?;
+    let _ = send_udp(socket, &out, peer).await?;
     Ok(())
 }
 
@@ -1494,7 +1523,7 @@ async fn handle_ticket_attach(
     };
     let body = protocol::to_body(&envelope)?;
     let out = protocol::encode_plain(PacketKind::AttachOk, client_id, 1, 0, &body)?;
-    socket.send_to(&out, peer).await?;
+    let _ = send_udp(socket, &out, peer).await?;
     Ok(())
 }
 
@@ -1512,7 +1541,7 @@ async fn send_reject_to_client(
         reason: reason.to_string(),
     })?;
     let out = protocol::encode_plain(PacketKind::AttachReject, client_id, 0, 0, &body)?;
-    socket.send_to(&out, peer).await?;
+    let _ = send_udp(socket, &out, peer).await?;
     Ok(())
 }
 
@@ -1578,7 +1607,7 @@ async fn handle_resume(
         SERVER_TO_CLIENT,
         &body,
     )?;
-    socket.send_to(&out, peer).await?;
+    let _ = send_udp(socket, &out, peer).await?;
     Ok(())
 }
 
@@ -1690,12 +1719,19 @@ async fn handle_ping(
         SERVER_TO_CLIENT,
         b"",
     )?;
-    socket.send_to(&out, peer).await?;
+    let _ = send_udp(socket, &out, peer).await?;
     Ok(())
 }
 
 async fn handle_detach(state: &Arc<Mutex<ServerState>>, packet: &protocol::Packet) -> Result<()> {
+    let (key, _) = find_client_decrypt_key(state, &packet.header)?;
+    let _ = protocol::decrypt_body(packet, &key, CLIENT_TO_SERVER)?;
     let mut locked = state.lock().expect("server state poisoned");
+    if let Some(client) = locked.client_mut(&packet.header.conn_id) {
+        if !client.replay.accept(packet.header.seq) {
+            return Ok(());
+        }
+    }
     locked.remove_client_everywhere(&packet.header.conn_id);
     Ok(())
 }
@@ -1705,6 +1741,14 @@ fn remove_client(state: &Arc<Mutex<ServerState>>, client_id: [u8; 16]) {
     locked.remove_client_everywhere(&client_id);
 }
 
+async fn send_udp(socket: &UdpSocket, packet: &[u8], peer: SocketAddr) -> Result<bool> {
+    match socket.send_to(packet, peer).await {
+        Ok(_) => Ok(true),
+        Err(err) if is_transient_udp_send_error(&err) => Ok(false),
+        Err(err) => Err(err).with_context(|| format!("send UDP packet to {peer}")),
+    }
+}
+
 async fn handle_ack(
     state: &Arc<Mutex<ServerState>>,
     peer: SocketAddr,
@@ -3020,7 +3064,7 @@ async fn send_stream_open_to_client(
         found
     };
     if let Some((endpoint, packet)) = send {
-        socket.send_to(&packet, endpoint).await?;
+        let _ = send_udp(socket, &packet, endpoint).await?;
     }
     Ok(())
 }
@@ -3114,7 +3158,7 @@ async fn queue_or_send_stream_data_to_client(
         send
     };
     if let Some((endpoint, packet)) = send {
-        socket.send_to(&packet, endpoint).await?;
+        let _ = send_udp(socket, &packet, endpoint).await?;
     }
     Ok(())
 }
@@ -3189,7 +3233,7 @@ async fn flush_stream_pending_data_to_client(
         let Some((endpoint, packet)) = send else {
             return Ok(());
         };
-        socket.send_to(&packet, endpoint).await?;
+        let _ = send_udp(socket, &packet, endpoint).await?;
     }
 }
 
@@ -3333,7 +3377,7 @@ async fn send_stream_packet_to_client(
         found
     };
     if let Some((endpoint, packet)) = send {
-        socket.send_to(&packet, endpoint).await?;
+        let _ = send_udp(socket, &packet, endpoint).await?;
     }
     Ok(())
 }
@@ -3435,7 +3479,7 @@ async fn broadcast_output(
         }
     }
     for (endpoint, packet) in sends {
-        socket.send_to(&packet, endpoint).await?;
+        let _ = send_udp(socket, &packet, endpoint).await?;
     }
     Ok(())
 }
@@ -3488,7 +3532,7 @@ async fn broadcast_session_exit(
         persist::remove_runtime_dir(&sessions_dir, &session_name);
     }
     for (endpoint, packet) in sends {
-        socket.send_to(&packet, endpoint).await?;
+        let _ = send_udp(socket, &packet, endpoint).await?;
     }
     Ok(())
 }
@@ -3595,7 +3639,7 @@ async fn retransmit_pending(
         sends
     };
     for (endpoint, packet) in sends {
-        socket.send_to(&packet, endpoint).await?;
+        let _ = send_udp(socket, &packet, endpoint).await?;
     }
     Ok(())
 }
@@ -3691,7 +3735,7 @@ async fn maybe_rekey_clients(
         sends
     };
     for (endpoint, packet) in sends {
-        socket.send_to(&packet, endpoint).await?;
+        let _ = send_udp(socket, &packet, endpoint).await?;
     }
     Ok(())
 }
@@ -3787,9 +3831,9 @@ fn cleanup_disconnected_clients(state: &Arc<Mutex<ServerState>>) {
             .iter()
             .filter(|(name, session)| {
                 !prewarm.contains(name.as_str())
-                    && session
-                        .empty_since
-                        .is_some_and(|since| now.duration_since(since) >= timeout)
+                    && session.empty_since.is_some_and(|since| {
+                        now.duration_since(since) >= empty_session_timeout(name, timeout)
+                    })
             })
             .map(|(name, _)| name.clone())
             .collect();
@@ -3808,6 +3852,14 @@ fn cleanup_disconnected_clients(state: &Arc<Mutex<ServerState>>) {
     }
 }
 
+fn empty_session_timeout(name: &str, configured_timeout: Duration) -> Duration {
+    if protocol::is_implicit_session_name(name) {
+        configured_timeout.min(Duration::from_secs(IMPLICIT_EMPTY_SESSION_GRACE_SECS))
+    } else {
+        configured_timeout
+    }
+}
+
 /// Select the client key (current or retained previous epoch) matching the
 /// packet header's `session_key_id`, so a packet sealed under the pre-rekey key
 /// during the grace window still decrypts while an expired/stale epoch is
@@ -3854,7 +3906,7 @@ mod tests {
     use super::*;
 
     #[test]
-    fn persists_named_sessions_when_enabled() {
+    fn persists_terminal_sessions_when_enabled() {
         let (pty_tx, _rx) = mpsc::unbounded_channel();
         let config = ServerConfig {
             persist_sessions: true,
@@ -3864,7 +3916,7 @@ mod tests {
         let state = ServerState::new(config, [0u8; 32], pty_tx);
         assert!(state.should_persist_session("default")); // prewarmed
         assert!(state.should_persist_session("work")); // explicitly named
-        assert!(!state.should_persist_session("term-1781470634216-76685")); // one-off terminal
+        assert!(state.should_persist_session("term-1781470634216-76685")); // one-off update-survivable terminal
     }
 
     #[test]
@@ -4019,6 +4071,12 @@ mod tests {
             Some((key, "work".to_string()))
         );
         assert!(state.client_mut(&client_id).is_some());
+        state.sessions.get_mut("work").unwrap().empty_since = Some(Instant::now());
+        state.insert_client("work", [7u8; 16], test_client_state([9u8; 32]));
+        assert!(
+            state.sessions["work"].empty_since.is_none(),
+            "reattach must clear empty-since so cleanup cannot reap a live session"
+        );
 
         // Removing purges both the session map and the index.
         assert!(state.remove_client_everywhere(&client_id));
@@ -4058,6 +4116,83 @@ mod tests {
         assert!(locked.lookup_client(&client_id).is_none());
     }
 
+    #[test]
+    fn implicit_empty_session_timeout_is_bounded_for_update_reconnect() {
+        let configured = Duration::from_secs(2_592_000);
+        let implicit = protocol::generate_implicit_session_name();
+        assert_eq!(
+            empty_session_timeout(&implicit, configured),
+            Duration::from_secs(IMPLICIT_EMPTY_SESSION_GRACE_SECS)
+        );
+        assert_eq!(
+            empty_session_timeout("work", configured),
+            configured,
+            "named sessions keep the normal long timeout"
+        );
+        assert_eq!(
+            empty_session_timeout(&implicit, Duration::from_secs(1)),
+            Duration::from_secs(1),
+            "tests/admins can still configure a shorter timeout"
+        );
+    }
+
+    #[tokio::test]
+    async fn forged_plaintext_detach_does_not_remove_client() {
+        let (pty_tx, _pty_rx) = mpsc::unbounded_channel();
+        let mut state = ServerState::new(ServerConfig::default(), [0u8; 32], pty_tx);
+        state
+            .ensure_session("work", 80, 24, "forward-only", &[])
+            .unwrap();
+        let client_id = [21u8; 16];
+        let session_key = [22u8; 32];
+        state.insert_client("work", client_id, test_client_state(session_key));
+        let state = Arc::new(Mutex::new(state));
+        let mut packet = protocol::decode(
+            &protocol::encode_plain(PacketKind::Detach, client_id, 1, 0, b"").unwrap(),
+        )
+        .unwrap();
+        packet.header.session_key_id = protocol::session_key_id(&session_key);
+
+        assert!(handle_detach(&state, &packet).await.is_err());
+
+        let locked = state.lock().unwrap();
+        assert!(
+            locked.lookup_client(&client_id).is_some(),
+            "plaintext detach with a copied key id must not remove a live client"
+        );
+    }
+
+    #[tokio::test]
+    async fn authenticated_detach_removes_client() {
+        let (pty_tx, _pty_rx) = mpsc::unbounded_channel();
+        let mut state = ServerState::new(ServerConfig::default(), [0u8; 32], pty_tx);
+        state
+            .ensure_session("work", 80, 24, "forward-only", &[])
+            .unwrap();
+        let client_id = [23u8; 16];
+        let session_key = [24u8; 32];
+        state.insert_client("work", client_id, test_client_state(session_key));
+        let state = Arc::new(Mutex::new(state));
+        let packet = protocol::decode(
+            &protocol::encode_encrypted(
+                PacketKind::Detach,
+                client_id,
+                1,
+                0,
+                &session_key,
+                CLIENT_TO_SERVER,
+                b"",
+            )
+            .unwrap(),
+        )
+        .unwrap();
+
+        handle_detach(&state, &packet).await.unwrap();
+
+        let locked = state.lock().unwrap();
+        assert!(locked.lookup_client(&client_id).is_none());
+    }
+
     #[tokio::test]
     async fn duplicate_stream_open_for_open_stream_resends_ok() {
         let (pty_tx, _pty_rx) = mpsc::unbounded_channel();
@@ -4536,4 +4671,25 @@ mod tests {
         };
         remote_bind_allowed(&config, "0.0.0.0").unwrap();
     }
+
+    #[cfg(unix)]
+    #[test]
+    fn server_udp_send_classifier_treats_network_roaming_errors_as_transient() {
+        for code in [
+            libc::EADDRNOTAVAIL,
+            libc::ECONNREFUSED,
+            libc::ECONNRESET,
+            libc::EHOSTDOWN,
+            libc::EHOSTUNREACH,
+            libc::ENETDOWN,
+            libc::ENETRESET,
+            libc::ENETUNREACH,
+            libc::ETIMEDOUT,
+        ] {
+            assert!(
+                is_transient_udp_send_error(&std::io::Error::from_raw_os_error(code)),
+                "expected errno {code} to be transient"
+            );
+        }
+    }
 }

src/lib.rs

@@ -23,3 +23,4 @@ pub mod pty;
 pub mod server;
 pub mod ssh_agent;
 pub mod transport;
+pub mod udp;

src/protocol.rs

@@ -280,7 +280,7 @@ pub fn decode(input: &[u8]) -> Result<Packet> {
 
 pub fn decrypt_body(packet: &Packet, key: &[u8; 32], direction: u32) -> Result<Vec<u8>> {
     if packet.header.flags & 1 == 0 {
-        return Ok(packet.body.clone());
+        bail!("packet body is not encrypted");
     }
     let nonce = crypto::nonce_from(direction, packet.header.seq);
     let aad = packet.header.aad();

src/server.rs

@@ -13,6 +13,7 @@ use crate::transport::{
     DoshTransport, SessionEvent, SessionRole, SessionTransportConfig, TransportConfig,
     service_name_from_target,
 };
+use crate::udp::is_transient_udp_send_error;
 use anyhow::{Context, Result, anyhow, bail};
 use ed25519_dalek::SigningKey;
 use std::collections::{HashMap, HashSet};
@@ -97,6 +98,7 @@ pub enum DoshServerEvent {
     Ignored,
 }
 
+#[derive(Debug, Clone)]
 struct PendingServerAuth {
     client: native::NativeClientHello,
     server: NativeServerHello,
@@ -255,7 +257,7 @@ impl DoshServer {
         };
         let body = protocol::to_body(&NativeServerHelloBody { hello })?;
         let out = protocol::encode_plain(PacketKind::NativeServerHello, pending_id, 1, 0, &body)?;
-        self.socket.send_to(&out, peer).await?;
+        let _ = send_udp(&self.socket, &out, peer).await?;
         Ok(())
     }
 
@@ -327,7 +329,7 @@ impl DoshServer {
         peer: SocketAddr,
         packet: &protocol::Packet,
     ) -> Result<DoshServerEvent> {
-        let Some(pending) = self.pending.remove(&packet.header.conn_id) else {
+        let Some(pending) = self.pending.get(&packet.header.conn_id).cloned() else {
             self.send_reject(peer, packet.header.conn_id, "unknown native auth")
                 .await?;
             return Ok(DoshServerEvent::Ignored);
@@ -338,13 +340,28 @@ impl DoshServer {
             return Ok(DoshServerEvent::Ignored);
         }
         if pending.created_at.elapsed() > self.config.auth_timeout {
+            self.pending.remove(&packet.header.conn_id);
             self.send_reject(peer, packet.header.conn_id, "native auth expired")
                 .await?;
             return Ok(DoshServerEvent::Ignored);
         }
 
-        let body = protocol::decrypt_body(packet, &pending.session_key, CLIENT_TO_SERVER)?;
-        let req: NativeUserAuthBody = protocol::from_body(&body)?;
+        let body = match protocol::decrypt_body(packet, &pending.session_key, CLIENT_TO_SERVER) {
+            Ok(body) => body,
+            Err(_) => {
+                self.send_reject(peer, packet.header.conn_id, "native auth decrypt failed")
+                    .await?;
+                return Ok(DoshServerEvent::Ignored);
+            }
+        };
+        let req: NativeUserAuthBody = match protocol::from_body(&body) {
+            Ok(req) => req,
+            Err(_) => {
+                self.send_reject(peer, packet.header.conn_id, "invalid native auth body")
+                    .await?;
+                return Ok(DoshServerEvent::Ignored);
+            }
+        };
         let services = match self.verify_auth_and_services(&pending, &req.auth) {
             Ok(services) => services,
             Err(err) => {
@@ -353,6 +370,7 @@ impl DoshServer {
                 return Ok(DoshServerEvent::Ignored);
             }
         };
+        self.pending.remove(&packet.header.conn_id);
 
         let conn_id = crypto::random_16();
         let key_id = protocol::session_key_id(&pending.session_key);
@@ -381,7 +399,7 @@ impl DoshServer {
             SERVER_TO_CLIENT,
             &body,
         )?;
-        self.socket.send_to(&out, peer).await?;
+        let _ = send_udp(&self.socket, &out, peer).await?;
 
         let transport = DoshTransport::new(
             Arc::clone(&self.socket),
@@ -428,7 +446,7 @@ impl DoshServer {
             reason: reason.to_string(),
         })?;
         let out = protocol::encode_plain(PacketKind::AttachReject, conn_id, 0, 0, &body)?;
-        self.socket.send_to(&out, peer).await?;
+        let _ = send_udp(&self.socket, &out, peer).await?;
         Ok(())
     }
 
@@ -439,6 +457,14 @@ impl DoshServer {
     }
 }
 
+async fn send_udp(socket: &UdpSocket, packet: &[u8], peer: SocketAddr) -> Result<bool> {
+    match socket.send_to(packet, peer).await {
+        Ok(_) => Ok(true),
+        Err(err) if is_transient_udp_send_error(&err) => Ok(false),
+        Err(err) => Err(err).with_context(|| format!("send UDP packet to {peer}")),
+    }
+}
+
 fn validate_requested_services(
     allowed_services: &HashSet<String>,
     requests: &[ForwardingRequest],
@@ -477,6 +503,7 @@ mod tests {
     use super::*;
     use crate::client::DoshClient;
     use crate::config::{ClientConfig, HostsConfig};
+    use crate::protocol::{CLIENT_TO_SERVER, NativeUserAuthBody};
     use crate::transport::TransportEvent;
     use ed25519_dalek::SigningKey;
 
@@ -588,4 +615,91 @@ mod tests {
             }
         }
     }
+
+    #[tokio::test]
+    async fn bad_native_auth_does_not_consume_pending_challenge() {
+        let dir = tempfile::tempdir().unwrap();
+        let host_key = dir.path().join("host_key");
+        let authorized_keys = dir.path().join("authorized_keys");
+        let signing = SigningKey::from_bytes(&[93u8; 32]);
+        let keypair = ssh_key::private::Ed25519Keypair::from(&signing);
+        let private =
+            ssh_key::PrivateKey::new(ssh_key::private::KeypairData::from(keypair), "").unwrap();
+        std::fs::write(
+            &authorized_keys,
+            format!("{}\n", private.public_key().to_openssh().unwrap()),
+        )
+        .unwrap();
+
+        let server_config = ServerConfig {
+            host_key: host_key.to_string_lossy().to_string(),
+            authorized_keys: vec![authorized_keys.to_string_lossy().to_string()],
+            ..ServerConfig::default()
+        };
+        let server_config = DoshServerConfig::new(server_config)
+            .bind_addr("127.0.0.1:0".parse().unwrap())
+            .require_current_user(false);
+        let mut server = DoshServer::bind(server_config).await.unwrap();
+        let peer: SocketAddr = "127.0.0.1:9".parse().unwrap();
+        let (client_secret, client_public) = native::generate_native_ephemeral();
+        let hello = native::NativeClientHello {
+            protocol_version: native::NATIVE_PROTOCOL_VERSION,
+            client_random: crypto::random_32(),
+            client_ephemeral_public: client_public,
+            requested_host: "127.0.0.1".to_string(),
+            requested_user: "sdk-user".to_string(),
+            requested_session: "test".to_string(),
+            requested_mode: "forward-only".to_string(),
+            terminal_size: (80, 24),
+            supported_aead: vec!["chacha20poly1305".to_string()],
+            supported_user_key_algorithms: vec!["ssh-ed25519".to_string()],
+            cached_host_key_fingerprint: None,
+            attach_ticket_envelope: None,
+            requested_env: Vec::new(),
+        };
+        let (pending_id, server_hello) = server.build_server_hello(hello.clone(), peer).unwrap();
+        let session_key = native::derive_native_session_key(
+            &client_secret,
+            server_hello.server_ephemeral_public,
+            &hello,
+            &server_hello,
+        )
+        .unwrap();
+        let auth = native::sign_user_auth(&signing, &hello, &server_hello, Vec::new()).unwrap();
+        let body = protocol::to_body(&NativeUserAuthBody { auth }).unwrap();
+        let bad = protocol::encode_encrypted(
+            PacketKind::NativeUserAuth,
+            pending_id,
+            2,
+            1,
+            &[7u8; 32],
+            CLIENT_TO_SERVER,
+            &body,
+        )
+        .unwrap();
+        let bad = protocol::decode(&bad).unwrap();
+
+        assert!(matches!(
+            server.handle_user_auth(peer, &bad).await.unwrap(),
+            DoshServerEvent::Ignored
+        ));
+        assert!(server.pending.contains_key(&pending_id));
+
+        let valid = protocol::encode_encrypted(
+            PacketKind::NativeUserAuth,
+            pending_id,
+            2,
+            1,
+            &session_key,
+            CLIENT_TO_SERVER,
+            &body,
+        )
+        .unwrap();
+        let valid = protocol::decode(&valid).unwrap();
+        assert!(matches!(
+            server.handle_user_auth(peer, &valid).await.unwrap(),
+            DoshServerEvent::Accepted(_)
+        ));
+        assert!(!server.pending.contains_key(&pending_id));
+    }
 }

src/transport.rs

@@ -19,6 +19,7 @@ use crate::protocol::{
     self, CLIENT_TO_SERVER, PacketKind, ReplayWindow, SERVER_TO_CLIENT, StreamClose, StreamData,
     StreamOpen, StreamOpenOk, StreamOpenReject, StreamWindowAdjust,
 };
+use crate::udp::is_transient_udp_send_error;
 use anyhow::{Result, anyhow, bail};
 use std::collections::{BTreeMap, HashMap, HashSet, VecDeque};
 use std::net::SocketAddr;
@@ -348,8 +349,8 @@ impl StreamMux {
         &mut self,
         adjust: StreamWindowAdjust,
     ) -> Result<Vec<OutgoingStreamPacket>> {
-        self.ack_data(adjust.stream_id, adjust.received_offset);
-        self.add_credit(adjust.stream_id, adjust.bytes as usize);
+        let acked_bytes = self.ack_data(adjust.stream_id, adjust.received_offset);
+        self.add_credit(adjust.stream_id, acked_bytes);
         self.flush_pending_data(adjust.stream_id)
     }
 
@@ -556,9 +557,9 @@ impl StreamMux {
         (chunks, consumed, *expected)
     }
 
-    fn ack_data(&mut self, stream_id: u64, received_offset: u64) {
+    fn ack_data(&mut self, stream_id: u64, received_offset: u64) -> usize {
         let Some(sent) = self.sent_data.get_mut(&stream_id) else {
-            return;
+            return 0;
         };
         let acked_offsets = sent
             .iter()
@@ -567,12 +568,16 @@ impl StreamMux {
                 (end <= received_offset).then_some(*offset)
             })
             .collect::<Vec<_>>();
+        let mut acked_bytes = 0usize;
         for offset in acked_offsets {
-            sent.remove(&offset);
+            if let Some(chunk) = sent.remove(&offset) {
+                acked_bytes = acked_bytes.saturating_add(chunk.bytes.len());
+            }
         }
         if sent.is_empty() {
             self.sent_data.remove(&stream_id);
         }
+        acked_bytes
     }
 
     fn add_credit(&mut self, stream_id: u64, bytes: usize) {
@@ -732,11 +737,17 @@ impl DoshTransport {
             if packet.header.conn_id != self.conn_id {
                 continue;
             }
+            let plain = match protocol::decrypt_body(
+                &packet,
+                &self.session_key,
+                self.role.recv_direction(),
+            ) {
+                Ok(plain) => plain,
+                Err(_) => continue,
+            };
             if !self.replay.accept(packet.header.seq) {
                 continue;
             }
-            let plain =
-                protocol::decrypt_body(&packet, &self.session_key, self.role.recv_direction())?;
             self.peer_addr = peer;
             self.ack_seq = self.ack_seq.max(packet.header.seq);
             self.last_contact = Instant::now();
@@ -751,14 +762,21 @@ impl DoshTransport {
         datagram: &[u8],
         peer: SocketAddr,
     ) -> Result<SessionEvent> {
-        let packet = protocol::decode(datagram)?;
+        let packet = match protocol::decode(datagram) {
+            Ok(packet) => packet,
+            Err(_) => return Ok(SessionEvent::Ignored),
+        };
         if packet.header.conn_id != self.conn_id {
             return Ok(SessionEvent::Ignored);
         }
+        let plain =
+            match protocol::decrypt_body(&packet, &self.session_key, self.role.recv_direction()) {
+                Ok(plain) => plain,
+                Err(_) => return Ok(SessionEvent::Ignored),
+            };
         if !self.replay.accept(packet.header.seq) {
             return Ok(SessionEvent::Ignored);
         }
-        let plain = protocol::decrypt_body(&packet, &self.session_key, self.role.recv_direction())?;
         self.peer_addr = peer;
         self.ack_seq = self.ack_seq.max(packet.header.seq);
         self.last_contact = Instant::now();
@@ -815,7 +833,12 @@ impl DoshTransport {
 
     async fn send_kind(&mut self, kind: PacketKind, body: &[u8]) -> Result<()> {
         let encoded = self.encode_kind(kind, body)?;
-        self.socket.send_to(&encoded, self.peer_addr).await?;
+        if let Err(err) = self.socket.send_to(&encoded, self.peer_addr).await {
+            if is_transient_udp_send_error(&err) {
+                return Ok(());
+            }
+            return Err(err.into());
+        }
         Ok(())
     }
 
@@ -980,6 +1003,30 @@ mod tests {
         assert_eq!(data.bytes, b"!");
     }
 
+    #[test]
+    fn cumulative_window_adjust_restores_credit_even_if_delta_was_lost() {
+        let mut mux = StreamMux::new(TransportConfig {
+            initial_window: 5,
+            retransmit_after: Duration::from_secs(1),
+            ..TransportConfig::default()
+        });
+        mux.open_stream(1, "@dosh-test", 0).unwrap();
+        mux.handle_open_ok(StreamOpenOk { stream_id: 1 }).unwrap();
+        assert_eq!(mux.send_data(1, b"hello".to_vec()).unwrap().len(), 1);
+        assert_eq!(mux.send_credit[&1], 0);
+
+        let flushed = mux
+            .handle_window_adjust(StreamWindowAdjust {
+                stream_id: 1,
+                received_offset: 5,
+                bytes: 0,
+            })
+            .unwrap();
+        assert!(flushed.is_empty());
+        assert_eq!(mux.send_credit[&1], 5);
+        assert_eq!(mux.send_data(1, b"!".to_vec()).unwrap().len(), 1);
+    }
+
     #[test]
     fn handle_packet_decodes_and_dispatches_stream_packets() {
         let mut mux = StreamMux::new(TransportConfig::default());
@@ -1096,4 +1143,61 @@ mod tests {
         assert!(matches!(server.recv().await.unwrap(), SessionEvent::Ping));
         assert_eq!(server.peer_addr(), roaming_addr);
     }
+
+    #[tokio::test]
+    async fn unauthenticated_datagram_does_not_poison_replay_window() {
+        let socket = UdpSocket::bind("127.0.0.1:0").await.unwrap();
+        let peer: SocketAddr = "127.0.0.1:9".parse().unwrap();
+        let key = [11u8; 32];
+        let wrong_key = [12u8; 32];
+        let conn_id = [4u8; 16];
+        let mut transport = DoshTransport::new_owned(
+            socket,
+            SessionTransportConfig {
+                role: SessionRole::Client,
+                conn_id,
+                session_key: key,
+                peer_addr: peer,
+                initial_send_seq: 1,
+                initial_ack: 0,
+                stream: TransportConfig::default(),
+            },
+        );
+        let bad = protocol::encode_encrypted(
+            PacketKind::Pong,
+            conn_id,
+            9,
+            0,
+            &wrong_key,
+            SERVER_TO_CLIENT,
+            b"",
+        )
+        .unwrap();
+        let valid = protocol::encode_encrypted(
+            PacketKind::Pong,
+            conn_id,
+            9,
+            0,
+            &key,
+            SERVER_TO_CLIENT,
+            b"",
+        )
+        .unwrap();
+
+        assert!(matches!(
+            transport
+                .handle_datagram(b"not a dosh packet", peer)
+                .await
+                .unwrap(),
+            SessionEvent::Ignored
+        ));
+        assert!(matches!(
+            transport.handle_datagram(&bad, peer).await.unwrap(),
+            SessionEvent::Ignored
+        ));
+        assert!(matches!(
+            transport.handle_datagram(&valid, peer).await.unwrap(),
+            SessionEvent::Pong
+        ));
+    }
 }

src/udp.rs

@@ -0,0 +1,98 @@
+//! UDP error classification shared by Dosh clients, servers, and embedders.
+
+pub fn is_transient_udp_send_error(err: &std::io::Error) -> bool {
+    matches!(
+        err.kind(),
+        std::io::ErrorKind::Interrupted
+            | std::io::ErrorKind::TimedOut
+            | std::io::ErrorKind::WouldBlock
+    ) || err.raw_os_error().is_some_and(is_transient_udp_os_error)
+}
+
+#[cfg(unix)]
+fn is_transient_udp_os_error(code: i32) -> bool {
+    matches!(
+        code,
+        libc::EADDRNOTAVAIL
+            | libc::ECONNREFUSED
+            | libc::ECONNRESET
+            | libc::EHOSTDOWN
+            | libc::EHOSTUNREACH
+            | libc::ENETDOWN
+            | libc::ENETRESET
+            | libc::ENETUNREACH
+            | libc::ETIMEDOUT
+    )
+}
+
+#[cfg(windows)]
+fn is_transient_udp_os_error(code: i32) -> bool {
+    matches!(
+        code,
+        10049  // WSAEADDRNOTAVAIL
+            | 10050 // WSAENETDOWN
+            | 10051 // WSAENETUNREACH
+            | 10052 // WSAENETRESET
+            | 10054 // WSAECONNRESET
+            | 10060 // WSAETIMEDOUT
+            | 10061 // WSAECONNREFUSED
+            | 10064 // WSAEHOSTDOWN
+            | 10065 // WSAEHOSTUNREACH
+    )
+}
+
+#[cfg(not(any(unix, windows)))]
+fn is_transient_udp_os_error(_code: i32) -> bool {
+    false
+}
+
+#[cfg(test)]
+mod tests {
+    use super::is_transient_udp_send_error;
+
+    #[test]
+    fn classifies_portable_transient_send_errors() {
+        for kind in [
+            std::io::ErrorKind::Interrupted,
+            std::io::ErrorKind::TimedOut,
+            std::io::ErrorKind::WouldBlock,
+        ] {
+            assert!(is_transient_udp_send_error(&std::io::Error::from(kind)));
+        }
+        assert!(!is_transient_udp_send_error(&std::io::Error::from(
+            std::io::ErrorKind::PermissionDenied,
+        )));
+    }
+
+    #[cfg(unix)]
+    #[test]
+    fn classifies_unix_network_churn_as_transient() {
+        for code in [
+            libc::EADDRNOTAVAIL,
+            libc::ECONNREFUSED,
+            libc::ECONNRESET,
+            libc::EHOSTDOWN,
+            libc::EHOSTUNREACH,
+            libc::ENETDOWN,
+            libc::ENETRESET,
+            libc::ENETUNREACH,
+            libc::ETIMEDOUT,
+        ] {
+            assert!(is_transient_udp_send_error(
+                &std::io::Error::from_raw_os_error(code)
+            ));
+        }
+    }
+
+    #[cfg(windows)]
+    #[test]
+    fn classifies_windows_network_churn_as_transient() {
+        for code in [
+            10049, 10050, 10051, 10052, 10054, 10060, 10061, 10064, 10065,
+        ] {
+            assert!(is_transient_udp_send_error(
+                &std::io::Error::from_raw_os_error(code)
+            ));
+        }
+    }
+}

tests/integration_smoke.rs

@@ -18,7 +18,8 @@ use dosh::crypto;
 use dosh::native::{host_public_key, load_or_create_host_key, ssh_ed25519_public_blob, trust_host};
 use dosh::protocol::{
     self, AttachOk, AttachReject, BootstrapAttachRequest, CLIENT_TO_SERVER, Frame, Input,
-    PacketKind, Resize, ResumeRequest, SERVER_TO_CLIENT,
+    PacketKind, Resize, ResumeRequest, SERVER_TO_CLIENT, TicketAttachBody, TicketAttachEnvelope,
+    TicketAttachOkEnvelope,
 };
 use ed25519_dalek::{Signer, SigningKey, VerifyingKey};
 
@@ -530,6 +531,75 @@ fn direct_attach_session(
     (socket, bootstrap, ok)
 }
 
+fn ticket_attach_session(
+    socket: &UdpSocket,
+    port: u16,
+    bootstrap: &dosh::auth::BootstrapResponse,
+    session: &str,
+    mode: &str,
+) -> AttachOk {
+    let client_nonce = crypto::random_12();
+    let request_key = crypto::hkdf32(
+        &bootstrap.attach_ticket_psk,
+        &client_nonce,
+        b"dosh/ticket-attach-request/v1",
+    )
+    .unwrap();
+    let body = protocol::to_body(&TicketAttachBody {
+        session: session.to_string(),
+        mode: mode.to_string(),
+        cols: 80,
+        rows: 24,
+        requested_env: Vec::new(),
+    })
+    .unwrap();
+    let ciphertext = crypto::seal(
+        &request_key,
+        &client_nonce,
+        b"dosh-ticket-attach-request-v1",
+        &body,
+    )
+    .unwrap();
+    let envelope = TicketAttachEnvelope {
+        ticket: bootstrap.attach_ticket.clone(),
+        client_nonce,
+        ciphertext,
+    };
+    let packet = protocol::encode_plain(
+        PacketKind::TicketAttachRequest,
+        [0u8; 16],
+        1,
+        0,
+        &protocol::to_body(&envelope).unwrap(),
+    )
+    .unwrap();
+    socket
+        .send_to(&packet, format!("127.0.0.1:{port}"))
+        .unwrap();
+    let mut buf = [0u8; 65535];
+    let (n, _) = socket.recv_from(&mut buf).unwrap();
+    let packet = protocol::decode(&buf[..n]).unwrap();
+    assert_eq!(packet.header.kind, PacketKind::AttachOk);
+    let envelope: TicketAttachOkEnvelope = protocol::from_body(&packet.body).unwrap();
+    let mut salt = Vec::with_capacity(24);
+    salt.extend_from_slice(&client_nonce);
+    salt.extend_from_slice(&envelope.server_nonce);
+    let response_key = crypto::hkdf32(
+        &bootstrap.attach_ticket_psk,
+        &salt,
+        b"dosh/ticket-attach-ok/v1",
+    )
+    .unwrap();
+    let plain = crypto::open(
+        &response_key,
+        &envelope.server_nonce,
+        b"dosh-ticket-attach-ok-v1",
+        &envelope.ciphertext,
+    )
+    .unwrap();
+    protocol::from_body(&plain).unwrap()
+}
+
 #[allow(clippy::too_many_arguments)]
 fn send_encrypted(
     socket: &UdpSocket,
@@ -2733,7 +2803,7 @@ fn session_survives_server_restart_same_shell_and_screen() {
 }
 
 #[test]
-fn implicit_session_does_not_create_restart_holder() {
+fn implicit_session_survives_update_restart_via_ticket_reattach() {
     let dir = tempfile::tempdir().unwrap();
     let sessions_dir = dir.path().join("sessions");
     let port = free_udp_port();
@@ -2743,21 +2813,34 @@ fn implicit_session_does_not_create_restart_holder() {
     let mut server = start_server(&dir, &config);
     let (socket, bootstrap, ok) = direct_attach_session(&config, port, "read-write", &session);
     let key = bootstrap.session_key;
+    type_line(&socket, port, &ok, &key, 2, "cd /tmp\n");
     type_line(
         &socket,
         port,
         &ok,
         &key,
-        2,
+        3,
         "export IMPLICIT_MARK=implicit_restart_42\n",
     );
-    let _ = collect_frame_text(&socket, &key, 1000);
+    type_line(
+        &socket,
+        port,
+        &ok,
+        &key,
+        4,
+        "printf 'IMPLICIT_SCREEN_MARKER\\n'\n",
+    );
+    let pre = collect_frame_text(&socket, &key, 1500);
+    assert!(
+        pre.contains("IMPLICIT_SCREEN_MARKER"),
+        "implicit marker missing before restart: {pre:?}"
+    );
     thread::sleep(Duration::from_secs(3));
 
     let shell_pid_before = holder_shell_pid(&sessions_dir, &session);
     assert!(
-        shell_pid_before.is_none(),
-        "implicit sessions must not get persistent holders when persistence is enabled"
+        shell_pid_before.is_some(),
+        "implicit sessions must get temporary holders so active clients survive updates"
     );
 
     let _ = server.kill();
@@ -2765,34 +2848,78 @@ fn implicit_session_does_not_create_restart_holder() {
     thread::sleep(Duration::from_millis(300));
 
     let mut server = start_server(&dir, &config);
-    let (socket2, bootstrap2, ok2) = direct_attach_session(&config, port, "read-write", &session);
-    let key2 = bootstrap2.session_key;
+
+    let resume = ResumeRequest {
+        session: session.clone(),
+        last_rendered_seq: ok.initial_seq,
+        cols: 80,
+        rows: 24,
+    };
+    send_encrypted(
+        &socket,
+        port,
+        PacketKind::ResumeRequest,
+        ok.client_id,
+        5,
+        0,
+        &key,
+        &protocol::to_body(&resume).unwrap(),
+    );
+    let mut buf = [0u8; 65535];
+    let deadline = std::time::Instant::now() + Duration::from_secs(2);
+    loop {
+        assert!(
+            std::time::Instant::now() < deadline,
+            "old live resume did not receive unknown-client reject"
+        );
+        let (n, _) = socket.recv_from(&mut buf).unwrap();
+        let packet = protocol::decode(&buf[..n]).unwrap();
+        if packet.header.kind == PacketKind::Frame {
+            continue;
+        }
+        assert_eq!(packet.header.kind, PacketKind::AttachReject);
+        assert_eq!(packet.header.conn_id, ok.client_id);
+        break;
+    }
+
+    let ok2 = ticket_attach_session(&socket, port, &bootstrap, &session, "read-write");
+    let key2 = ok2.session_key;
+    let snapshot = String::from_utf8_lossy(&ok2.snapshot).to_string();
     type_line(
-        &socket2,
+        &socket,
         port,
         &ok2,
         &key2,
         2,
-        "printf 'IMPLICIT_MARK=%s\\n' \"$IMPLICIT_MARK\"\n",
+        "printf 'IMPLICIT_MARK=%s PWD=%s\\n' \"$IMPLICIT_MARK\" \"$PWD\"\n",
     );
-    let post = collect_frame_text(&socket2, &key2, 2000);
+    let post = collect_frame_text(&socket, &key2, 2000);
     let shell_pid_after = holder_shell_pid(&sessions_dir, &session);
 
     let _ = server.kill();
     let _ = server.wait();
+    kill_holder(&sessions_dir, &session);
 
     assert!(
-        shell_pid_after.is_none(),
-        "implicit restart attach must stay ephemeral"
+        snapshot.contains("IMPLICIT_SCREEN_MARKER"),
+        "ticket reattach snapshot must repaint the exact pre-update screen, got {snapshot:?}"
+    );
+    assert_eq!(
+        shell_pid_after, shell_pid_before,
+        "implicit update reconnect must use the same holder shell"
     );
     assert!(
-        post.contains("IMPLICIT_MARK=") && !post.contains("implicit_restart_42"),
-        "implicit session must start fresh after server restart, got {post:?}"
+        post.contains("IMPLICIT_MARK=implicit_restart_42"),
+        "implicit session env must survive update reconnect, got {post:?}"
+    );
+    assert!(
+        post.contains("PWD=/tmp"),
+        "implicit session cwd must survive update reconnect, got {post:?}"
     );
 }
 
 #[test]
-fn startup_discards_legacy_implicit_holders() {
+fn startup_readopts_implicit_holders_for_update_reconnect() {
     let dir = tempfile::tempdir().unwrap();
     let sessions_dir = dir.path().join("sessions");
     let port = free_udp_port();
@@ -2812,13 +2939,14 @@ fn startup_discards_legacy_implicit_holders() {
     let _ = server.kill();
     let _ = server.wait();
     assert!(
-        holder_shell_pid(&sessions_dir, &session).is_none(),
-        "startup must remove old implicit holder metadata"
+        holder_shell_pid(&sessions_dir, &session).is_some(),
+        "startup must keep live implicit holders so active update reconnects can reattach"
     );
     assert!(
-        unsafe { libc::kill(shell_pid, 0) } != 0,
-        "startup must shut down old implicit holder shell"
+        unsafe { libc::kill(shell_pid, 0) } == 0,
+        "startup must not shut down a live implicit holder before reconnect grace"
     );
+    kill_holder(&sessions_dir, &session);
 }
 
 #[test]

tests/protocol_auth.rs

@@ -58,6 +58,19 @@ fn encrypted_packet_round_trips() {
     assert_eq!(plain, b"hello");
 }
 
+#[test]
+fn plaintext_packet_never_decrypts_as_authenticated_body() {
+    let key = crypto::random_32();
+    let mut decoded = protocol::decode(
+        &protocol::encode_plain(PacketKind::Input, crypto::random_16(), 1, 0, b"hello").unwrap(),
+    )
+    .unwrap();
+    decoded.header.session_key_id = protocol::session_key_id(&key);
+
+    let err = protocol::decrypt_body(&decoded, &key, CLIENT_TO_SERVER).unwrap_err();
+    assert!(err.to_string().contains("not encrypted"));
+}
+
 #[test]
 fn encrypted_packet_rejects_wrong_session_key_id_before_decrypt() {
     let key = crypto::random_32();