fix(cli): prevent infinite loop in ghost text wrapping when inputWidth is narrower than a codepoint

[sridhar-3009]

Summary

Fixes #19985 — the CLI freezes when an @filename:line completion is active and the terminal is too narrow to display a wide character (e.g. an emoji rendered at width 2 in a 1-column window).

Root cause: getGhostTextLines in InputPrompt.tsx contains a while (stringWidth(wordToProcess) > inputWidth) loop that splits an oversized word into lines. An inner for-loop scans codepoints and advances splitIndex only when partWidth + charWidth <= inputWidth. When inputWidth is 0 — or smaller than a single codepoint's rendered width — no codepoint ever fits, so splitIndex stays 0. cpSlice(wordToProcess, 0) then returns the full word unchanged, and the outer while loops forever, freezing the renderer.

Fix: After the inner scan, if splitIndex is still 0 and the word is non-empty, force-advance by one codepoint. This guarantees the loop always makes progress and terminates.

// When inputWidth is narrower than a single codepoint, nothing
// fits and splitIndex stays 0, causing an infinite loop. Force-
// advance by one codepoint so the loop always terminates.
if (splitIndex === 0 && wordCP.length > 0) {
  part = wordCP[0];
  splitIndex = 1;
}

Test plan

• Added regression test does not freeze when ghost text contains wide chars and inputWidth is narrow in InputPrompt.test.tsx: sets inputWidth=1 with an emoji ghost text (😀, width 2), which would have hung the test runner before this fix
• pnpm test in packages/cli — existing suite passes

[gemini-code-assist]

Summary of Changes

Hello, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request addresses a critical issue where the CLI would freeze when rendering ghost text in extremely narrow terminal windows. By ensuring the text wrapping logic always makes progress even when individual characters exceed the available display width, the fix guarantees that the rendering loop terminates correctly.

Highlights

• Infinite Loop Prevention: Added a safety check in the ghost text wrapping logic to force-advance by one codepoint when the input width is too narrow to fit any characters, preventing an infinite loop.
• Regression Testing: Implemented a new test case in InputPrompt.test.tsx that simulates a narrow terminal window with wide characters to ensure the CLI remains responsive.

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[github-actions]

📊 PR Size: size/S

• Lines changed: 44
• Additions: +44
• Deletions: -0
• Files changed: 2

[gemini-code-assist]

Code Review

This pull request fixes an infinite loop bug in InputPrompt that occurs when wrapping ghost text containing wide characters (such as emojis) when the inputWidth is narrower than the character's rendered width. It resolves this by force-advancing the loop by one codepoint if no characters fit. A regression test has also been added to verify this behavior. I have no feedback to provide as there are no review comments.