tui: input area covered by black rectangle during heavy tool-call/reasoning on v2 #38773

Description

Summary

In TUI mode on the v2 branch, the input field (and slightly above it) is
intermittently covered by a solid black rectangle, blocking text entry. The
issue occurs consistently when the model performs many tool calls or extended
reasoning. The only workaround is re-entering the session.

Expected Behavior

The input area should remain visible and usable at all times, regardless of
model activity.

Actual Behavior

A black rectangle occludes the input field and a small region above it after
the model initiates several tool calls or extensive reasoning. The rest of
the chat history remains visible. Re-entering the session (connecting again)
clears the artifact.

Additional Context

• Frequency: Consistent – reproduces every session when the model does
  many tool calls or long reasoning chains.
• First noticed: On the v2 branch only (the opencode2 binary); did not
  occur on v1.
• Workarounds tried: Re-entering the session (only known workaround).
  Resizing the terminal window and pressing Escape do not help.
• Logs: ~/.local/share/opencode/log/opencode.log shows no errors or
  warnings related to rendering – only standard INFO-level startup and
  keepalive messages.
• Terminal: Ghostty with OpenGL renderer. Other terminal features
  (ligatures, truecolor, etc.) work correctly.

Plugins

No response

OpenCode version

opencode version: opencode2-node v0.0.0+46ff404 (prod channel)

Steps to reproduce

1. Open opencode in TUI mode (run opencode without subcommands).
2. Start a session with a model that uses tool calls or spends significant
   time reasoning (e.g. multiple sequential tool calls).
3. While the model is producing tool calls or reasoning output, observe the
   input area at the bottom of the terminal.
4. At some point the input field (and a couple of lines above it) becomes
   covered by a solid black rectangle, making it impossible to type or see
   the prompt.

Screenshot and/or share link

Operating System

OS: Linux 7.1.3-cachyos-lto (NixOS, x86_64)

Terminal

Terminal: Ghostty 1.3.2-dev (GTK/OpenGL renderer),