Fix text prompt underlines in Windows consoles

[amcaplan]

WHY are these changes introduced?

Text prompts draw their underline with the upper one eighth block character (▔), which is unsupported by legacy Windows console fonts used with cmd and PowerShell.

WHAT is this pull request doing?

Use an Ink Box single top border on Windows in both TextPrompt and DangerousConfirmationPrompt. Ink draws the standard horizontal line (─) and handles its width, preserving indentation and idle/error colors. Keep the original ▔ underline on macOS and Linux.

Add rendering coverage for Windows, macOS, and Linux in normal and validation-error states, and include a patch changeset.

How to test your changes?

Validated locally:

• All 26 tests in TextPrompt.test.tsx and DangerousConfirmationPrompt.test.tsx pass.
• ESLint passes for the four changed TypeScript files.
• CLI kit tsc --noEmit and git diff --check pass.

For manual verification, open a CLI text prompt in cmd or PowerShell, enter text, and trigger a validation error. Confirm the underline renders as a continuous line and changes from cyan to red. Native Windows console testing has not been performed on this macOS machine.

Checklist

• I've considered possible cross-platform impacts (Mac, Linux, Windows)
• I've considered possible documentation changes
• I've considered analytics changes to measure impact
• The change is user-facing and includes a patch changeset

[amcaplan]

/snapit

[github-actions]

🫰✨ Thanks @amcaplan! Your snapshot has been published to npm.

Test the snapshot by installing your package globally:

pnpm i -g --@shopify:registry=https://registry.npmjs.org @shopify/cli@0.0.0-snapshot-20260907163636

Caution

After installing, validate the version by running shopify version in your terminal.
If the versions don't match, you might have multiple global instances installed.
Use which shopify to find out which one you are running and uninstall it.

[amcaplan]

Before:

After:

As mentioned above, only Windows is affected; Mac/Linux are unchanged.

[Copilot]

🟢 Approval recommended

The changes are small, platform-scoped, align with existing layout patterns, and include targeted cross-platform rendering assertions plus a patch changeset.

Pull request overview

This PR updates CLI Kit’s Ink-based text prompt components to render underlines correctly in legacy Windows console fonts. It switches from using the ▔ character (often unsupported in cmd/PowerShell fonts) to an Ink Box top border on Windows, while preserving the existing underline rendering on macOS/Linux, and adds cross-platform rendering tests plus a patch changeset.

Changes:

• Render prompt underlines using an Ink Box single top border on Windows for TextPrompt and DangerousConfirmationPrompt.
• Preserve existing ▔ underline rendering on non-Windows platforms.
• Add tests covering Windows/macOS/Linux underline rendering and color change on validation error; include a patch changeset.

File summaries

File	Description
packages/cli-kit/src/private/node/ui/components/TextPrompt.tsx	Switch underline rendering to an Ink top border on Windows; keep ▔ underline elsewhere.
packages/cli-kit/src/private/node/ui/components/TextPrompt.test.tsx	Mock platform detection and add parameterized tests validating underline rendering across OSes.
packages/cli-kit/src/private/node/ui/components/DangerousConfirmationPrompt.tsx	Apply the same Windows underline approach to the dangerous confirmation prompt.
packages/cli-kit/src/private/node/ui/components/DangerousConfirmationPrompt.test.tsx	Add platform-aware underline rendering tests for the dangerous confirmation prompt.
.changeset/windows-prompt-underline.md	Patch changeset documenting the Windows underline rendering fix.

Review details

• Files reviewed: 5/5 changed files
• Comments generated: 0
• Review effort level: Lite

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