TUI crashes (Bun segfault) when the terminal shrinks to extreme sizes (~2×1) #38199

What happened
Dragging the pane hosting opencode 1.18.4 down to an extreme size (approaching 2 cols × 1 row,
rapid SIGWINCH/TIOCSWINSZ stream) crashes the process — "Bun has crashed / Segmentation fault",
exit 1. Two independent hits, same stack family (JSC microtask drain, generator microtasks):

• https://bun.report/1.3.14/Ma10d9b296mwGugogC________urh5kDunr21Cusw11C+/y34C+qy34C+5sy6Cu657H__urh5kD27p5tC+xt2yCA2K4/vshtD
• https://bun.report/1.3.14/Ma10d9b296mwGugogC_______2lkjlDurh5kDunr21Cusw11C+/y34C+qy34C+5sy6Cu657H__urh5kD27p5tC+xt2yCA2K4/ny3zD

Environment: macOS aarch64, host = xterm.js in a Tauri app over a PTY (portable-pty).
A session was open (conversation view rendered). Filed the VM side as oven-sh/bun#35010 as well —
a Bun VM shouldn't segfault on whatever the TUI does — but opentui likely also wants a
defensive minimum-size clamp in its layout so pathological grids can't drive that path.

Repro honesty: reliable in our real app at extreme shrink; ~10 headless PTY variants
(staircase drags, floor jitter at 1–4 cols, query replies, mouse-motion floods) did NOT
reproduce, so exact timing/state in the terminal byte stream matters.

Workaround that works: floor the grid the host reports to the PTY (we use 20×5 and clip
visually below that) — real terminals never offer a TUI 2×1 either.