A pty/ctl winsize gives a terminal two rows at least, so it no longer reads busy for ever

A one-row pty loses the prompt's input mark as soon as the prompt wraps,
and busy detection never sees the shell idle again. Placement already
keeps a new terminal at tag + 2 rows; a winsize write now keeps the pty
at two. A pane dragged down to one body row keeps a one-row pty, since
a taller pty than the pane shows would put its cursor below the pane.

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

1 files changed, 6 insertions, 1 deletions

diff --git a/src/ninep/pty.zig b/src/ninep/pty.zig
index 046a456a..4009af49 100644
--- a/src/ninep/pty.zig
+++ b/src/ninep/pty.zig
@@ -28,6 +28,9 @@ fn dimension(word: []const u8) ?u16 {
     return if (n == 0 or n > winsize_max) null else n;
 }
 
+/// The fewest rows a winsize write gives a terminal's pty.
+pub const pty_rows_min = 2;
+
 /// As the root ctl's `size` (4096 a side).
 const winsize_max = 4096;
 const e_winsize_range = std.fmt.comptimePrint("invalid winsize: out of range, 1x1 to {d}x{d}", .{ winsize_max, winsize_max });
@@ -71,7 +74,9 @@ fn verb(p: *Pardes, id: usize, line: []const u8, apply: bool) bool {
     switch (v) {
         .winsize => {
             const cols = dimension(words.next() orelse return false) orelse return false;
-            const rows = dimension(words.next() orelse return false) orelse return false;
+            // Two rows at least, as a pane is laid out: a one-row pty
+            // loses its prompt's input mark and reads busy for ever.
+            const rows = @max(pty_rows_min, dimension(words.next() orelse return false) orelse return false);
             if (words.next() != null) return false;
             if (!apply) return true;
             p.emit(.{ .resize_pty = .{ .pane = @intCast(id), .cols = cols, .rows = rows } });