test: check what a real terminal renders for multi, zellij, and the TUI

tests/16-render.sh runs tmux, zellij, and the TUI in xterm on Xvfb,
takes screenshots, and reads them back with tesseract: remote prompts
in all panes, borders and titles with the hosts, [SYNC] appearing and
disappearing, panes side by side, broadcast output in every pane and
input in one pane only without it, windows split by panes_per_window,
the status bar, and TUI marks. Screenshots stay in testenv/.artifacts.

OCR reads three preprocessing variants (plain, stretched for dim gray,
brightest channel for colored text) and normalizes characters that
DejaVu Sans Mono makes ambiguous (1/l, C/().

The screenshots showed tmux cutting the session name in the status bar
to "[netssh-pv"; netssh multi now widens status-left-length for its
own session.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

internal/multiplex/multiplex_test.go

@@ -133,6 +133,7 @@ func TestTmuxOutsideSplitsWindowsAndAvoidsSessionNames(t *testing.T) {
 		"tmux has-session -t =netssh-pve-2",
 		"tmux new-session -d -x 240 -y 70 -s netssh-pve-2 -P -F #{window_id} #{pane_id} -n pve-1 ",
 		"tmux new-window -t netssh-pve-2: -P -F #{window_id} #{pane_id} -n pve-2 ",
+		"tmux set-option -t netssh-pve-2 status-left-length 40",
 	} {
 		if !strings.Contains(joined, want) {
 			t.Errorf("missing %q in\n%s", want, joined)

internal/multiplex/tmux.go

@@ -42,6 +42,13 @@ func openTmux(panes []Pane, opts Options, r Runner) error {
 		if err != nil {
 			return err
 		}
+		if !inside && i == 0 {
+			// tmux cuts the status bar's session name at 10 characters
+			// ("[netssh-pv"); widen it for this session only.
+			if _, err := r.Output("tmux", "set-option", "-t", session, "status-left-length", "40"); err != nil {
+				return err
+			}
+		}
 		window, pane, _ := strings.Cut(out, " ")
 		if first == "" {
 			first = window