TUI: stale/duplicated text after long sessions in embedded terminals (Orca); full buffer clear fixes it longer than partial redraw

During long sessions the TUI screen gradually "falls apart": duplicated/stale fragments of text overlap current content, similar to #41458, #47255, #48714, but it appears after a long session (lots of streamed output) rather than immediately.

Observed environment:

• macOS (Apple Silicon), Orca (Electron-based IDE with an embedded xterm.js terminal), Orca terminal pane as the only "terminal"
• opencode 1.18.30 (Homebrew, brew install opencode)
• No tmux, no plugins involved in the rendering itself

Workarounds and their effect:

1. ctrl+p (command list) — opens a dialog, forces a full TUI redraw; fixes the screen but only briefly.
2. Full terminal buffer clear (Orca keybinding terminal.clear, Mod+K — clears the xterm.js pane incl. scrollback via the PTY) — fixes it for a much longer time.

The difference between (1) and (2) suggests the corruption accumulates in the terminal emulator's scrollback buffer (garbage from many incremental TUI redraws), and a TUI-side redraw alone can't get rid of it — only wiping the emulator buffer does.

Questions / hypotheses:

• Is there a way to force a full repaint from a clean screen state (e.g. re-emit the whole screen instead of relative cursor updates) via a keybind or env var?
• Should the TUI periodically do a full absolute re-render, or emit a clear-sequence when it detects its cursor model may have desynced from the terminal?

Steps to reproduce:

1. Run opencode in an embedded/web terminal (Orca, or any xterm.js-based embed)
2. Have a long session with lots of streamed responses
3. Watch for overlapping/stale text; confirm ctrl+p fixes briefly, full terminal buffer clear fixes for longer

OpenCode version: 1.18.30