Keep live TUI output raw under retransmit pressure

src/bin/dosh-server.rs

@@ -3336,7 +3336,7 @@ async fn broadcast_output(
     let sends = {
         let mut locked = state.lock().expect("server state poisoned");
         let scrollback = locked.config.scrollback;
-        let retransmit_window = locked.config.retransmit_window;
+        let retransmit_window = locked.config.retransmit_window.max(1);
         let session = locked
             .sessions
             .get_mut(&output.session)
@@ -3374,20 +3374,18 @@ async fn broadcast_output(
             client.send_seq += 1;
             // Count traffic toward the packet-count rekey trigger (spec §11).
             client.epoch_packets = client.epoch_packets.saturating_add(1);
-            // Only materialize a screen snapshot when this client has fallen too
-            // far behind; the common case sends the raw output bytes and must not
-            // clone the whole vt100 grid per client per packet.
-            let (bytes, snapshot) = if client.pending.len() >= retransmit_window {
-                client.pending.clear();
-                (screen_snapshot(session.parser.screen()), true)
-            } else {
-                (output.bytes.clone(), false)
-            };
+            // Live terminal bytes are never rewritten into vt100 snapshots. A
+            // snapshot is useful for attach/resume, but substituting it during a
+            // running TUI can lose graph/background-cell details that apps like
+            // btop rely on. If retransmit history is full, prune only history.
+            while client.pending.len() >= retransmit_window {
+                client.pending.pop_front();
+            }
             let frame = Frame {
                 session: output.session.clone(),
                 output_seq,
-                bytes,
-                snapshot,
+                bytes: output.bytes.clone(),
+                snapshot: false,
                 closed: false,
             };
             let body = protocol::to_body(&frame)?;
@@ -3400,9 +3398,6 @@ async fn broadcast_output(
                 SERVER_TO_CLIENT,
                 &body,
             )?;
-            while client.pending.len() >= retransmit_window {
-                client.pending.pop_front();
-            }
             client.pending.push_back(PendingFrame {
                 output_seq,
                 packet: packet.clone(),