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fix(cli): cap pending plain text height to reduce streaming flicker #29629

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fix(cli): cap pending plain text height to reduce streaming flicker #29629

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601c4f7
fix(cli): cap pending plain text height to reduce streaming flicker
shamanshetty07 Oct 4, 2026
73f9b1c
Merge branch 'main' into fix/pending-text-height-flicker
shamanshetty07 Oct 7, 2026
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39 changes: 39 additions & 0 deletions packages/cli/src/ui/utils/MarkdownDisplay.test.tsx
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Original file line number Diff line number Diff line change
Expand Up @@ -87,6 +87,45 @@ describe('<MarkdownDisplay />', () => {
unmount();
});

it('caps the height of pending plain text to the available height', async () => {
const text = Array.from(
{ length: 30 },
(_, i) => `${i + 1}. tip ${i + 1}`,
).join(eol);
const { lastFrame, unmount } = await renderWithProviders(
<MarkdownDisplay
{...baseProps}
text={text}
isPending={true}
availableTerminalHeight={10}
/>,
);
const frame = lastFrame() ?? '';
expect(frame.trimEnd().split('\n').length).toBeLessThanOrEqual(10);
expect(frame).toContain('tip 30');
expect(frame).not.toContain('tip 1\n');
expect(frame).toContain('lines hidden');
unmount();
});

it('does not cap the height of completed plain text', async () => {
const text = Array.from(
{ length: 30 },
(_, i) => `${i + 1}. tip ${i + 1}`,
).join(eol);
const { lastFrame, unmount } = await renderWithProviders(
<MarkdownDisplay
{...baseProps}
text={text}
isPending={false}
availableTerminalHeight={10}
/>,
);
expect(lastFrame()).toContain('tip 1');
expect(lastFrame()).toContain('tip 30');
unmount();
});

it('renders unordered lists with different markers', async () => {
const text = `
- item A
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20 changes: 20 additions & 0 deletions packages/cli/src/ui/utils/MarkdownDisplay.tsx
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Original file line number Diff line number Diff line change
Expand Up @@ -12,6 +12,7 @@ import { TableRenderer } from './TableRenderer.js';
import { RenderInline } from './InlineMarkdownRenderer.js';
import { useSettings } from '../contexts/SettingsContext.js';
import { useAlternateBuffer } from '../hooks/useAlternateBuffer.js';
import { MaxSizedBox } from '../components/shared/MaxSizedBox.js';

interface MarkdownDisplayProps {
text: string;
Expand Down Expand Up @@ -311,6 +312,25 @@ const MarkdownDisplayInternal: React.FC<MarkdownDisplayProps> = ({
);
}

// When not in alternate buffer mode a pending message that is taller than the
// terminal forces Ink to clear and redraw the whole screen on every update.
// Cap the height so streaming text keeps the frame shorter than the terminal.
if (
!isAlternateBuffer &&
isPending &&
availableTerminalHeight !== undefined
) {
return (
<MaxSizedBox
maxHeight={availableTerminalHeight}
maxWidth={terminalWidth}
overflowDirection="top"
>
{contentBlocks}
</MaxSizedBox>
);
}

return <>{contentBlocks}</>;
};

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