TUI: prompt box reserves 8 blank rows in narrow terminals when the footer wraps #44551

Description

On a narrow terminal, the prompt box at the bottom of the TUI reserves a large block of blank rows that nothing is drawn into. At 50 columns it takes 15 rows, 8 of which are blank — roughly a third of the screen on a phone-sized terminal.

It correlates with how much the prompt footer wraps. The same session, same terminal size, with and without --auto (which adds the auto chip to the footer and pushes it from 3 wrapped lines to 4):

opencode --auto -s <session> at 50x40 — prompt box is 15 rows, rows 29-36 are blank:

12	     ▣  Build · Ox Alpha Free (Unlimited) · 9.5s
13
...	     (message area, blank)
21
22	  ┃
23	  ┃
24	  ┃
25	  ┃  Builauto·Ox Alpha Free (Unlimited) Ope·m
26	  ┃  d                                  nCo a
27	  ┃                                     de  x
28	  ┃                                     Zen
29	  ┃
30	  ┃
31	  ┃
32	  ┃
33	  ┃
34	  ┃
35	  ┃
36	  ┃
37	  ╹▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀
38	   /Users/hiroyuki/           24.9K (2ctrl+p
39	   CascadeProjects/totteta            commands

opencode -s <session> at 50x40 (same session, no --auto) — prompt box is 6 rows, no blank rows:

12	     ▣  Build · Ox Alpha Free (Unlimited) · 9.5s
13
...	     (message area, blank)
30
31	  ┃
32	  ┃
33	  ┃
34	  ┃  Buil ·Ox Alpha Free (Unlimited) OpenC· ma
35	  ┃  d                               ode Z  x
36	  ┃                                  en
37	  ╹▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀
38	   /Users/hiroyuki/           24.9K (2ctrl+p
39	   CascadeProjects/totteta            commands

Measurements

All on one session with a single short exchange (message area does not fill the viewport), pane size set with tmux new-session -x/-y.

Width sweep, height fixed at 40, with --auto:

Height sweep, width fixed at 50, with --auto: 30, 40 and 60 rows all give a 15-row prompt box. The wasted height is constant, not proportional to the terminal.

Two more data points:

• It does not reproduce once the conversation is long enough to fill the viewport — the prompt box collapses back to 4-5 rows. The box seems to absorb leftover vertical space and over-reserves when the footer wraps.
• A fresh session on a shorter model name (DeepSeek V4 Flash / OpenCode Go, no variant chip) does not reproduce at 50x40 even with --auto, because the footer only wraps to 2 lines. So the trigger looks like total footer width rather than --auto specifically.

prompt.max_height in tui.json has no effect on this. I tested unset, 3 and 20 at 50x24 and got the same box height in all three.

Steps to reproduce

1. Start a session and send one short message, so the message area does not fill the screen.
2. Reopen that session in a 50x40 terminal with a long model name and the auto permission chip visible, e.g. opencode --auto -s <session-id>.
3. The prompt footer wraps to 4 lines and the prompt box takes 15 rows, the last 8 of which are blank.
4. Reopen the same session without --auto. The footer wraps to 3 lines and the prompt box takes 6 rows.

Environment

• OpenCode 1.18.21
• macOS 26.6.2
• tmux (pane sized with -x/-y); originally hit through Mosh from an iPhone, which is where a 50-column terminal is normal
• Plugins: opencode-sentinel