A run whose output a redraw moved above its start answers cut, never an empty whole

pty/run reads a command's output between its C and D marks. When the
end landed at or before the start, it answered `exit 0` with no output,
as if nothing was printed. That happens when the shell redraws its prompt
over the output, as it can in a window two rows high (winsize 10 2). Now
only equal marks mean nothing was printed. An end at the top-left cell
or above the start says `cut`, since how much was printed is not known.

bash, fish, long lines and 3000-line outputs at winsize 10 2 all came
back whole on this build, so the dogfood's loss could not be reproduced
directly. The test drives the marks into the inverted case the loss
needs.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

1 files changed, 7 insertions, 2 deletions

diff --git a/src/terminal.zig b/src/terminal.zig
index 1a3b6a21..4cac6f1d 100644
--- a/src/terminal.zig
+++ b/src/terminal.zig
@@ -1044,9 +1044,14 @@ pub fn commandOutput(pane: *Pane, gpa: std.mem.Allocator, max_rows: usize) !Comm
         const screen = state.vt.screens.get(.primary) orelse break :printed false;
         if (end.garbage) break :printed false;
         var whole = !marks.lost and !start.garbage;
+        // Nothing printed: the whole of it.
+        if (start.eql(end.*)) break :printed whole;
         // D is where the next prompt begins: the output ends a cell before.
-        const last = end.leftWrap(1) orelse break :printed whole;
-        if (start.eql(end.*) or last.before(start.*)) break :printed whole;
+        // An end at the very top, or before the start, is output a redraw
+        // moved (a prompt drawn over it in a window two rows high): how
+        // much is not known, so it is not called whole.
+        const last = end.leftWrap(1) orelse break :printed false;
+        if (last.before(start.*)) break :printed false;
         var from = start.*;
         if (last.up(max_rows)) |floor| if (from.before(floor)) {
             from = floor;