[FEATURE]: Add cursor_style configuration support in tui.json

[Retromadee]

Verification

• I searched for existing feature requests.
• I discussed this in Discord (if there's an existing conversation).

Description

OpenCode currently hardcodes terminal escape sequences that force a block cursor shape, ignoring the native terminal cursor configuration (commonly beam/vertical line in Terminal.app, iTerm2, and other emulators). The TUI initialization in @opentui/core sets terminal raw mode and emits default escape sequences that reset user cursor preferences.

Proposed Solution

Expose a cursor_style key in tui.json config that accepts one of three values - beam, underline, or block - and emits the corresponding DECSCUSR escape codes during terminal initialization.

Example config:

{
  "$schema": "https://opencode.ai/tui.json",
  "cursor_style": "beam"
}

Alternative solutions

• A settings popup in the TUI itself.
• Using an environment variable to configure cursor shape.

[github-actions]

This issue doesn't fully meet our contributing guidelines.

What needs to be fixed:

• The issue does not use the required Feature Request template. Please resubmit using the template, which requires a verification checkbox confirming the feature hasn't been suggested before, and a title starting with [FEATURE]:.

Please edit this issue to address the above within 2 hours, or it will be automatically closed.

---

This issue might be a duplicate of existing issues. Please check:

• [FEATURE]: Allow changing cursor style from block to bar/line #11738: Allow changing cursor style from block to bar/line (same request: configurable cursor style with beam/underline/block options and DECSCUSR escape codes)
• [FEATURE]:Cursor Style ' Vertical Line (Terminal) #38926: [FEATURE]: Cursor Style Vertical Line (Terminal) — also filed by you an hour earlier, covering the same underlying request

If you believe this was flagged incorrectly, please let a maintainer know.

[github-actions]

This issue still doesn't meet our contributing guidelines — the body only contains the placeholder text "Please edit this issue to conform to the template." with no actual content.

What still needs to be fixed:

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The issue currently has no template and no real information. Please edit it with the appropriate template and real content. The needs:compliance label will remain until this is addressed.

[github-actions]

Thanks for updating the issue! It now follows the feature request template with a clear description of the problem and a well-defined proposed solution. The needs:compliance label has been removed.