TUI: cursor jank during streaming/scroll + occasional bottom-pane drift

What version of Codex CLI is running?

codex-cli 0.99.0-alpha.9

What subscription do you have?

Pro

Which model were you using?

gpt-5.2-codex

What platform is your computer?

Linux 6.17.0-12-generic x86_64

What terminal emulator and version are you using (if applicable)?

Gnome Terminal

What issue are you seeing?

While the output is streaming, the terminal cursor visibly jumps/blinks during scroll updates, and bottom-pane anchoring looks unstable under heavy text output streams.

Proposed fix

• Hide the terminal cursor while writing wrapped output into scrollback.
• Split flex allocation behavior:
• FitContent for desired_height()
• FillAssignedExtent for render() / cursor_pos()

What steps can reproduce the bug?

1. Send a long streaming prompt (e.g. "write a 50 stanza poem").
2. Watch cursor + bottom pane as output scrolls.

What is the expected behavior?

Expected
Cursor stays visually stable and composer/footer remain anchored.

Actual
Visible cursor jank during streaming/scroll and occasional anchoring instability.