Two render-polish fixes for codex sessions in the terminal write pipeline:
- flushPendingWrites uses a 32KB first-frame budget for codex (vs 64KB for
other modes). Codex's TUI emits dense synchronized redraws during
thinking/high-effort phases; a smaller first frame keeps per-frame
xterm/WebGL stalls short and avoids multi-second main-thread blocks.
- Sticky-scroll now honours a short grace window after a manual scroll-up
gesture (USER_SCROLL_STICKY_SUPPRESS_MS = 1500ms). High-frequency codex
"Working (Ns)" status ticks were snapping the viewport back to the bottom
while the user tried to read earlier output. The wheel/touch scroll
handlers record the gesture (_noteTerminalUserScroll); flushPendingWrites
suppresses the auto-scroll-to-bottom and restores the preserved viewport
via scrollToLine while the grace window is active.
Adds test/terminal-flush-budget.test.ts (vm-sandbox harness over
terminal-ui.js): codex vs non-codex first-frame budget, buffer-load
ownership, and the scroll-up suppression / viewport restore.
Co-Authored-By: Saqeb Akhter <saqeb.akhter@gmail.com>
