diff --git a/regress/output-history-loss.sh b/regress/output-history-loss.sh
new file mode 100644
index 000000000..6bbd2404f
--- /dev/null
+++ b/regress/output-history-loss.sh
@@ -0,0 +1,79 @@
+#!/bin/sh
+
+. ./input-common.inc
+
+# A multiline command evicts its prompt before producing output.
+command='\033]133;A\007p>\033]133;B\007echo\n'
+i=0
+while [ "$i" -lt 30 ]; do
+	command="${command}continued command\n"
+	i=$((i + 1))
+done
+OUTPUT=$(printf 'one\ntwo')
+
+for state in complete unfinished next-prompt; do
+	seq="${command}zz\033]133;C\007one\ntwo"
+	case "$state" in
+	complete|next-prompt)
+		seq="${seq}\033]133;D;0\007separator"
+		;;
+	esac
+	if [ "$state" = next-prompt ]; then
+		seq="${seq}\n\033]133;A\007p>\033]133;B\007"
+	fi
+	start_pane_hlimit lost 40 5 "$seq" 3
+	check_raw_matches lost 'START_OUTPUT.*osc133=0,0,2,0,0'
+	if [ "$state" != next-prompt ]; then
+		check_raw_no_matches lost 'START_PROMPT'
+	fi
+	if [ "$state" != unfinished ]; then
+		check_raw_matches lost 'END_OUTPUT.*osc133=0,0,0,3,0'
+	fi
+
+	for position in inside after; do
+		for keys in emacs vi; do
+			$TMUX set-option -w -t lost: mode-keys "$keys" ||
+			    exit 1
+			$TMUX copy-mode -t lost: || exit 1
+			if [ "$position" = inside ]; then
+				$TMUX send-keys -t lost: -X search-backward one ||
+				    exit 1
+			fi
+			$TMUX set-buffer sentinel || exit 1
+			$TMUX send-keys -t lost: -X copy-output || exit 1
+			$TMUX save-buffer "$TMP" || exit 1
+			printf '%s' "$OUTPUT" >"$EXP"
+			cmp "$TMP" "$EXP" ||
+			    fail "$state $position $keys output"
+
+			$TMUX send-keys -t lost: -X select-output || exit 1
+			present=$($TMUX display-message -p -t lost: \
+			    '#{selection_present}')
+			if [ "$present" != 1 ]; then
+				echo "FAIL: $state $position $keys no selection"
+				exit_status=1
+			fi
+			$TMUX set-buffer sentinel || exit 1
+			$TMUX send-keys -t lost: -X copy-selection || exit 1
+			$TMUX save-buffer "$TMP" || exit 1
+			cmp "$TMP" "$EXP" ||
+			    fail "$state $position $keys selection"
+			$TMUX send-keys -t lost: -X cancel || exit 1
+		done
+	done
+done
+
+# Retained command text does not belong to a later prompt's output.
+seq="${command}\033]133;A\007p>\033]133;B\007echo\n"
+seq="${seq}\033]133;C\007later\033]133;D;0\007"
+start_pane_hlimit later 40 5 "$seq" 3
+$TMUX copy-mode -t later: || exit 1
+$TMUX send-keys -t later: -X history-top || exit 1
+$TMUX set-buffer sentinel || exit 1
+$TMUX send-keys -t later: -X copy-output || exit 1
+[ "$($TMUX show-buffer)" = sentinel ] || exit 1
+$TMUX send-keys -t later: -X select-output || exit 1
+[ "$($TMUX display-message -p -t later: '#{selection_present}')" = 0 ] ||
+    exit 1
+
+exit $exit_status
diff --git a/regress/output-osc133-reflow.sh b/regress/output-osc133-reflow.sh
new file mode 100644
index 000000000..20bd211c8
--- /dev/null
+++ b/regress/output-osc133-reflow.sh
@@ -0,0 +1,145 @@
+#!/bin/sh
+
+. ./input-common.inc
+
+check_output()
+{
+	name=$1
+	expected=$2
+
+	$TMUX copy-mode -t "$name:" || exit 1
+	$TMUX send-keys -t "$name:" -X search-backward echo || exit 1
+	$TMUX set-buffer sentinel || exit 1
+	$TMUX send-keys -t "$name:" -X copy-output || exit 1
+	$TMUX save-buffer "$TMP" || exit 1
+	printf '%s' "$expected" >"$EXP"
+	cmp "$TMP" "$EXP" || fail "$name output"
+	$TMUX send-keys -t "$name:" -X cancel || exit 1
+}
+
+check_selection()
+{
+	name=$1
+	expected=$2
+
+	for keys in emacs vi; do
+		$TMUX set-option -w -t "$name:" mode-keys "$keys" || exit 1
+		$TMUX copy-mode -t "$name:" || exit 1
+		$TMUX send-keys -t "$name:" -X search-backward echo || exit 1
+		$TMUX send-keys -t "$name:" -X select-output || exit 1
+		$TMUX set-buffer sentinel || exit 1
+		$TMUX send-keys -t "$name:" -X copy-selection || exit 1
+		$TMUX save-buffer "$TMP" || exit 1
+		printf '%s' "$expected" >"$EXP"
+		cmp "$TMP" "$EXP" || fail "$name $keys selection"
+		$TMUX send-keys -t "$name:" -X cancel || exit 1
+	done
+}
+
+check_pipe()
+{
+	name=$1
+	expected=$2
+
+	$TMUX copy-mode -t "$name:" || exit 1
+	$TMUX send-keys -t "$name:" -X search-backward echo || exit 1
+	printf '%s' "$expected" >"$EXP"
+	: >"$TMP"
+	$TMUX send-keys -t "$name:" -X pipe-output "cat >'$TMP'" || exit 1
+	i=0
+	while [ "$i" -lt 50 ]; do
+		cmp -s "$TMP" "$EXP" && break
+		sleep 0.1
+		i=$((i + 1))
+	done
+	cmp "$TMP" "$EXP" || fail "$name pipe"
+	$TMUX send-keys -t "$name:" -X cancel || exit 1
+}
+
+prompt='\033]133;A\007p>\033]133;B\007echo\n'
+next='\n\033]133;A\007p>\033]133;B\007'
+short=$(printf '%060d' 0)
+long=$(printf '%0120d' 0)
+
+# Completed output keeps its end marker when split or joined.
+for payload in "$short" "$long"; do
+	seq="${prompt}\033]133;C\007${payload}"
+	seq="${seq}\033]133;D;7\007${next}"
+	start_pane_history resize 80 20 "$seq"
+	for width in 80 40 100 160 40 80; do
+		$TMUX resize-window -t resize: -x "$width" || exit 1
+		check_output resize "$payload"
+	done
+	check_selection resize "$payload"
+	check_pipe resize "$payload"
+done
+
+# Nonzero columns and cuts exactly at marker positions.
+seq='xx\033]133;A\007p>\033]133;B\007echo'
+seq="${seq}\033]133;C\007output\033]133;D;9\007tail"
+start_pane_history columns 80 20 "$seq"
+$TMUX resize-window -t columns: -x 8 || exit 1
+check_raw_matches columns \
+    'L 0 .*flags=WRAPPED,START_PROMPT,START_COMMAND.*osc133=2,4,0,0,0' \
+    'L 1 .*flags=WRAPPED,START_OUTPUT,END_OUTPUT.*osc133=0,0,0,6,9'
+check_output columns output
+$TMUX resize-window -t columns: -x 10 || exit 1
+check_raw_matches columns \
+    'L 0 .*START_PROMPT,START_COMMAND,START_OUTPUT.*osc133=2,4,8,0,0' \
+    'L 1 .*flags=END_OUTPUT.*osc133=0,0,0,4,9'
+check_output columns output
+$TMUX resize-window -t columns: -x 14 || exit 1
+check_raw_matches columns \
+    'L 1 .*flags=END_OUTPUT.*osc133=0,0,0,0,9'
+check_output columns output
+$TMUX resize-window -t columns: -x 80 || exit 1
+check_raw_matches columns \
+    'L 0 .*START_COMMAND,START_OUTPUT,END_OUTPUT.*osc133=2,4,8,14,9'
+
+start_pane_history secondary 80 20 'abcdefgh\033]133;P;k=s\007more'
+$TMUX resize-window -t secondary: -x 8 || exit 1
+check_raw_matches secondary 'L 1 .*flags=SECOND_PROMPT.*osc133=0,0,0,0,0'
+$TMUX resize-window -t secondary: -x 80 || exit 1
+check_raw_matches secondary 'L 0 .*flags=SECOND_PROMPT.*osc133=8,0,0,0,0'
+
+# A marker-only line must survive resizing.
+start_pane_history empty 8 20 \
+    "${prompt}\033]133;C\007abcdefgh\n\033]133;D;3\007"
+$TMUX resize-window -t empty: -x 4 || exit 1
+$TMUX resize-window -t empty: -x 16 || exit 1
+expected=$(printf 'abcdefgh\n_')
+check_output empty "${expected%_}"
+check_raw_matches empty \
+    'flags=START_OUTPUT.*osc133=0,0,0,0,0' \
+    'flags=END_OUTPUT.*0/0 osc133=0,0,0,0,3'
+
+# UTF-8 cells use the same offsets as the text moved by reflow.
+LC_ALL=C.UTF-8
+export LC_ALL
+wide=$(printf '\347\225\214a\347\225\214b\347\225\214c')
+start_pane_history wide 80 20 \
+    "${prompt}zzx\033]133;C\007${wide}\033]133;D;5\007${next}"
+for width in 3 6; do
+	$TMUX resize-window -t wide: -x "$width" || exit 1
+	check_raw_matches wide \
+	    "START_OUTPUT.*osc133=0,0,$((3 % width)),0,0" \
+	    'END_OUTPUT.*osc133=0,0,0,[0-9]+,5'
+	$TMUX resize-window -t wide: -x 80 || exit 1
+	check_output wide "$wide"
+done
+check_selection wide "$wide"
+
+# Unfinished output includes retained text beyond and below the cursor.
+start_pane_history unfinished 80 20 "${prompt}\033]133;C\007abcdefgh\rxy"
+check_output unfinished xycdefgh
+check_selection unfinished xycdefgh
+check_pipe unfinished xycdefgh
+
+start_pane_history below 80 20 \
+    "${prompt}\033]133;C\007first\n\nlast\033[2A\rXY"
+expected=$(printf 'XYrst\n\nlast')
+check_output below "$expected"
+check_selection below "$expected"
+check_pipe below "$expected"
+
+exit $exit_status