feat(cli): truncate shell command output in history

Refines the display of shell command outputs in the history to prevent
excessive vertical scrolling and improve readability.

Key changes:
- Implemented pruneShellOutput utility in textUtils to safely truncate
  strings and AnsiOutput arrays.
- Updated useShellCommandProcessor to prune shell execution results to
  a maximum of 10 lines before adding them to the history.
- Updated toolMapping to apply truncation to run_shell_command results
  when mapping core status to display status.
- Added maxLines prop to AnsiOutputText and ToolResultDisplay components
  to enforce line limits during rendering.
- Configured ShellToolMessage to pass a 10-line limit to the display component.

This ensures that long shell outputs are truncated in the UI history while
retaining the full output for the model context.

packages/cli/src/ui/components/AnsiOutput.tsx

@@ -14,18 +14,25 @@ interface AnsiOutputProps {
   data: AnsiOutput;
   availableTerminalHeight?: number;
   width: number;
+  maxLines?: number;
 }
 
 export const AnsiOutputText: React.FC<AnsiOutputProps> = ({
   data,
   availableTerminalHeight,
   width,
+  maxLines,
 }) => {
-  const lastLines = data.slice(
-    -(availableTerminalHeight && availableTerminalHeight > 0
+  const effectiveHeight =
+    availableTerminalHeight && availableTerminalHeight > 0
       ? availableTerminalHeight
-      : DEFAULT_HEIGHT),
-  );
+      : (maxLines ?? DEFAULT_HEIGHT);
+
+  const limit = maxLines
+    ? Math.min(effectiveHeight, maxLines)
+    : effectiveHeight;
+
+  const lastLines = data.slice(-limit);
   return (
     <Box flexDirection="column" width={width} flexShrink={0}>
       {lastLines.map((line: AnsiLine, lineIndex: number) => (

packages/cli/src/ui/components/messages/ShellToolMessage.tsx

@@ -153,6 +153,7 @@ export const ShellToolMessage: React.FC<ShellToolMessageProps> = ({
           availableTerminalHeight={availableTerminalHeight}
           terminalWidth={terminalWidth}
           renderOutputAsMarkdown={renderOutputAsMarkdown}
+          maxLines={10}
         />
         {isThisShellFocused && config && (
           <Box paddingLeft={STATUS_INDICATOR_WIDTH} marginTop={1}>

packages/cli/src/ui/components/messages/ToolResultDisplay.tsx

@@ -27,6 +27,7 @@ export interface ToolResultDisplayProps {
   availableTerminalHeight?: number;
   terminalWidth: number;
   renderOutputAsMarkdown?: boolean;
+  maxLines?: number;
 }
 
 interface FileDiffResult {
@@ -39,16 +40,21 @@ export const ToolResultDisplay: React.FC<ToolResultDisplayProps> = ({
   availableTerminalHeight,
   terminalWidth,
   renderOutputAsMarkdown = true,
+  maxLines,
 }) => {
   const { renderMarkdown } = useUIState();
 
-  const availableHeight = availableTerminalHeight
+  let availableHeight = availableTerminalHeight
     ? Math.max(
         availableTerminalHeight - STATIC_HEIGHT - RESERVED_LINE_COUNT,
         MIN_LINES_SHOWN + 1, // enforce minimum lines shown
       )
     : undefined;
 
+  if (maxLines && availableHeight) {
+    availableHeight = Math.min(availableHeight, maxLines);
+  }
+
   const combinedPaddingAndBorderWidth = 4;
   const childWidth = terminalWidth - combinedPaddingAndBorderWidth;
 
@@ -107,6 +113,7 @@ export const ToolResultDisplay: React.FC<ToolResultDisplayProps> = ({
         data={truncatedResultDisplay as AnsiOutput}
         availableTerminalHeight={availableHeight}
         width={childWidth}
+        maxLines={maxLines}
       />
     );
   }

packages/cli/src/ui/hooks/shellCommandProcessor.test.tsx

@@ -43,7 +43,9 @@ vi.mock('node:os', async (importOriginal) => {
   };
 });
 vi.mock('node:crypto');
-vi.mock('../utils/textUtils.js');
+vi.mock('../utils/textUtils.js', () => ({
+  pruneShellOutput: vi.fn((output) => output),
+}));
 
 import {
   useShellCommandProcessor,

packages/cli/src/ui/hooks/shellCommandProcessor.ts

@@ -26,8 +26,10 @@ import path from 'node:path';
 import os from 'node:os';
 import fs from 'node:fs';
 import { themeManager } from '../../ui/themes/theme-manager.js';
+import { pruneShellOutput } from '../utils/textUtils.js';
 
 export const OUTPUT_UPDATE_INTERVAL_MS = 1000;
+const MAX_OUTPUT_LINES_HISTORY = 10;
 const MAX_OUTPUT_LENGTH = 10000;
 
 function addShellCommandToGeminiHistory(
@@ -284,7 +286,10 @@ export const useShellCommandProcessor = (
               const finalToolDisplay: IndividualToolCallDisplay = {
                 ...initialToolDisplay,
                 status: finalStatus,
-                resultDisplay: finalOutput,
+                resultDisplay: pruneShellOutput(
+                  finalOutput,
+                  MAX_OUTPUT_LINES_HISTORY,
+                ),
               };
 
               // Add the complete, contextual result to the local UI history.

packages/cli/src/ui/hooks/toolMapping.ts

@@ -17,6 +17,9 @@ import {
   type HistoryItemToolGroup,
   type IndividualToolCallDisplay,
 } from '../types.js';
+import { pruneShellOutput } from '../utils/textUtils.js';
+
+const MAX_OUTPUT_LINES_HISTORY = 10;
 
 import { checkExhaustive } from '../../utils/checks.js';
 
@@ -117,7 +120,10 @@ export function mapToDisplay(
     return {
       ...baseDisplayProperties,
       status: mapCoreStatusToDisplayStatus(call.status),
-      resultDisplay,
+      resultDisplay:
+        call.request.name === 'run_shell_command'
+          ? pruneShellOutput(resultDisplay, MAX_OUTPUT_LINES_HISTORY)
+          : resultDisplay,
       confirmationDetails,
       outputFile,
       ptyId,

packages/cli/src/ui/utils/textUtils.ts

@@ -10,6 +10,32 @@ import { stripVTControlCharacters } from 'node:util';
 import stringWidth from 'string-width';
 import { LRUCache } from 'mnemonist';
 import { LRU_BUFFER_PERF_CACHE_LIMIT } from '../constants.js';
+import type { AnsiOutput, ToolResultDisplay } from '@google/gemini-cli-core';
+
+/**
+ * Prunes shell output to the last N lines.
+ * Handles both string output and AnsiOutput object.
+ */
+export function pruneShellOutput(
+  output: ToolResultDisplay | undefined,
+  maxLines: number,
+): ToolResultDisplay | undefined {
+  if (output === undefined) return undefined;
+
+  if (typeof output === 'string') {
+    const lines = output.split('\n');
+    if (lines.length <= maxLines) return output;
+    return lines.slice(-maxLines).join('\n');
+  }
+
+  if (Array.isArray(output)) {
+    // Assume it's AnsiOutput (AnsiLine[])
+    if (output.length <= maxLines) return output;
+    return output.slice(-maxLines) as AnsiOutput;
+  }
+
+  return output;
+}
 
 /**
  * Calculates the maximum width of a multi-line ASCII art string.