[BUG] /tui fullscreen clips shell-details footer and output box without tmux (plain iTerm2)

Preflight Checklist

• [x] I have searched existing issues and this hasn't been reported yet
• [x] This is a single bug report (please file separate reports for different bugs)
• [x] I am using the latest version of Claude Code

What's Wrong?

With "tui": "fullscreen" enabled, the shell-details view (opened from /tasks for a background shell) renders clipped:

• The details panel renders inline below the transcript instead of taking over the viewport; the output box gets only the leftover height (e.g. "Showing 9 lines")
• The footer ("← to go back · Esc/Enter/Space to close · x to stop") is not pinned to the bottom row — it flows with content and is clipped below the viewport, so I must resize the window taller to reach it
• The Output box appears to be a static snapshot taken at open time: watching a ping, the view stayed at icmp_seq=10-18 while the process had already reached seq 25+, even though Status showed "running"

This reproduces on plain iTerm2 with NO tmux/multiplexer, so it is not (only) about multiplexer chrome. Closely related to #51497 (tmux-specific, closed as stale with no response) — this report rules out "doesn't account for tmux status bar" as the sole root cause. A wide-and-short terminal window (ultrawide monitor) makes it much worse.

Workaround: switching back to the default /tui mode fixes the clipping entirely — the shell view then takes over the screen properly (confirmed by side-by-side testing).

(Supersedes #74321, which I filed without the template and closed.)

What Should Happen?

Entering shell details is an explicit "watch this shell" action, so the view should take over the full viewport (like less/htop), pin the footer to the bottom row, and live-tail the output while the shell is running.

Error Messages/Logs

No error messages — visual/layout issue. The shell-details view shows e.g. "Showing 9 lines" with the footer ("← to go back · Esc/Enter/Space to close · x to stop") clipped below the viewport.

Steps to Reproduce

1. Use a terminal window that is wide but short (easiest way to see the clipping; ultrawide monitor)
2. Enable fullscreen TUI: /tui fullscreen (or "tui": "fullscreen" in ~/.claude/settings.json)
3. Ask Claude to run a long-lived background shell, e.g. ping -i 1 8.8.8.8 (run in background)
4. Open the shell from the /tasks (or /bashes) list to enter the shell-details view
5. Observe: output box shrinks to a few lines ("Showing 9 lines"), footer is clipped below the viewport, and the output does not update while the shell keeps running
6. Switch back to default /tui mode and repeat steps 3-4: the view renders correctly

Claude Model

None

Is this a regression?

I don't know

Last Working Version

_No response_

Claude Code Version

2.1.201

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

iTerm2

Additional Information

_No response_