From 6806af7db30fb4a627be5f4204e353199f4ba078 Mon Sep 17 00:00:00 2001
From: Anurag Kumar Singh <dr.anuragkr@gmail.com>
Date: Mon, 7 Sep 2026 22:50:32 +0530
Subject: [PATCH] fix(cli): prevent ghost text wrapping infinite loop at narrow
 widths

Fixes #19985

When inputWidth is narrower than a single character's rendered width
(e.g. wide CJK or emoji characters in narrow terminal widths), splitIndex
remains 0 in getGhostTextLines and wordToProcess never shrinks, causing
an infinite while loop that pegs CPU at 100% and freezes the prompt.

Force-advance by at least one code point when splitIndex is 0 so the
hard-split loop is guaranteed to terminate. Adds a regression unit test.
---
 .../src/ui/components/InputPrompt.test.tsx    | 35 +++++++++++++++++++
 .../cli/src/ui/components/InputPrompt.tsx     |  7 ++++
 2 files changed, 42 insertions(+)

diff --git a/packages/cli/src/ui/components/InputPrompt.test.tsx b/packages/cli/src/ui/components/InputPrompt.test.tsx
index a2b0788f939..7bfbdbfd87f 100644
--- a/packages/cli/src/ui/components/InputPrompt.test.tsx
+++ b/packages/cli/src/ui/components/InputPrompt.test.tsx
@@ -5394,6 +5394,41 @@ describe('InputPrompt', () => {
     });
   });
 
+  describe('ghost text wrapping', () => {
+    it('does not freeze when ghost text contains wide chars and inputWidth is narrow', async () => {
+      // Regression for #19985: when inputWidth is smaller than a wide
+      // character's rendered width, the hard-split loop must still advance.
+      // buffer.text must be non-empty so getGhostTextLines does not early-return.
+      props.inputWidth = 1;
+      props.suggestionsWidth = 1;
+      mockedUseCommandCompletion.mockReturnValue({
+        ...mockCommandCompletion,
+        promptCompletion: {
+          text: 'a' + '好'.repeat(10),
+          accept: vi.fn(),
+          clear: vi.fn(),
+          isLoading: false,
+          isActive: true,
+          markSelected: vi.fn(),
+        },
+      });
+      mockBuffer.text = 'a';
+      mockBuffer.lines = ['a'];
+      mockBuffer.cursor = [0, 1];
+
+      const { lastFrame, unmount } = await renderWithProviders(
+        <TestInputPrompt {...props} />,
+        { uiState: {} },
+      );
+
+      // Without the guard this hang pegs CPU and the wait times out.
+      await waitFor(() => {
+        expect(lastFrame()).toBeDefined();
+      });
+      unmount();
+    });
+  });
+
   describe('terminal buffer rendering', () => {
     it('does not clip the last char of a visual line whose width equals inputWidth', async () => {
       const fullLine = '1234567890'; // 10 chars, exactly props.inputWidth
diff --git a/packages/cli/src/ui/components/InputPrompt.tsx b/packages/cli/src/ui/components/InputPrompt.tsx
index 511c4b6ceb6..d7e7eb80b62 100644
--- a/packages/cli/src/ui/components/InputPrompt.tsx
+++ b/packages/cli/src/ui/components/InputPrompt.tsx
@@ -1515,6 +1515,13 @@ export const InputPrompt: React.FC<InputPromptProps> = ({
                 partWidth += charWidth;
                 splitIndex = i + 1;
               }
+              // 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;
+              }
               additionalLines.push(part);
               wordToProcess = cpSlice(wordToProcess, splitIndex);
             }