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

Preflight Checklist

• [x] I have searched existing issues and this hasn't been reported yet (closest is #51497, which is tmux-specific and was closed as stale — this report reproduces without tmux)
• [x] This is a single bug report
• [x] I am using the latest version of Claude Code (v2.1.201)

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 as #51497's title suggests. A wide-and-short terminal window (ultrawide monitor) makes it much worse.

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.

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).

Error Messages/Logs

(no errors — visual/layout issue; output box shows e.g. "Showing 9 lines" with the footer clipped below the viewport)

Steps to Reproduce

1. Use a terminal window that is wide but short (easiest way to see the clipping)
2. Enable fullscreen TUI: /tui fullscreen
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, footer is below the viewport, output does not update while the shell keeps running

Environment

• Claude Code version: v2.1.201 (native install)
• Platform: macOS 26.5 (Darwin 25.5.0)
• Terminal: iTerm2 3.6.11, TERM=xterm-256color
• Multiplexer: none (no tmux/screen)
• Settings: "tui": "fullscreen" in ~/.claude/settings.json