Flicker while "thinking" on Windows (regression of #158); amplified by block cursor (#2507)

[JeffSteinbok]

Describe the bug

Copilot CLI flickers while it's "thinking" (during model/tool work). The flicker is per-frame redraws of the spinner/status area and is visible the entire time the agent is processing. This is a regression of #158 (which was closed) and reproduces on the latest CLI on Windows.

The flicker is particularly noticeable because Copilot CLI overrides the terminal cursor to a block/box shape (see #2507). The wider cell of the box cursor repaints more visibly than the thin bar the terminal is configured to use, so each redraw flashes a larger area. Users whose terminals are otherwise configured to a bar cursor see a much more jarring effect inside Copilot CLI than at the PowerShell prompt outside of it.

/experimental on does not resolve it.

Affected version

GitHub Copilot CLI 1.0.66 (latest as of filing).

Environment

• OS: Windows 11 Enterprise Insider Preview 10.0.26310
• Terminal: Windows Terminal 1.24.11321.0
• Shell: PowerShell 7.6.3
• cursorShape is not set in settings.json (Windows Terminal default = bar). Cursor at the PowerShell prompt is a bar; inside Copilot CLI it becomes a block.
• Reproduces on multiple Windows machines after updating to 1.0.66.

Steps to reproduce

1. Launch copilot in Windows Terminal + PowerShell 7.
2. Ask it to do any non-trivial task that requires a few seconds of model thinking or tool calls.
3. Observe the spinner/status line flickering for the duration of "thinking".

Expected behavior

Steady rendering of the spinner/status area; no per-frame full-row flash.

Additional context

• Related closed issue: Flickering while thinking of tasks #158 (flickering while thinking) — same symptom, appears regressed.
• Related closed issue: Screen flickers with cursor blink when selecting No, and tell Copilot what to do differently option #1202 (cursor-blink flicker during input prompts).
• Related open issue: Respect terminal defaults for cursor style, or at least follow standard UX conventions #2507 (Copilot CLI overrides cursor shape to block) — this magnifies the visible flicker area.
• /experimental on does not fix the issue.