Addressed case with 0 terminal height

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

@@ -35,7 +35,11 @@ export const AnsiOutputText: React.FC<AnsiOutputProps> = ({
       ? Math.min(availableHeightLimit, maxLines)
       : (availableHeightLimit ?? maxLines ?? DEFAULT_HEIGHT);
 
-  const lastLines = disableTruncation ? data : data.slice(-numLinesRetained);
+  const lastLines = disableTruncation
+    ? data
+    : numLinesRetained === 0
+      ? []
+      : data.slice(-numLinesRetained);
   return (
     <Box flexDirection="column" width={width} flexShrink={0} overflow="hidden">
       {lastLines.map((line: AnsiLine, lineIndex: number) => (

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

@@ -87,7 +87,7 @@ export const ToolResultDisplay: React.FC<ToolResultDisplayProps> = ({
       if (text.length > MAXIMUM_RESULT_DISPLAY_CHARACTERS) {
         text = '...' + text.slice(-MAXIMUM_RESULT_DISPLAY_CHARACTERS);
       }
-      if (maxLines) {
+      if (maxLines !== undefined) {
         const hasTrailingNewline = text.endsWith('\n');
         const contentText = hasTrailingNewline ? text.slice(0, -1) : text;
         const lines = contentText.split('\n');
@@ -103,7 +103,11 @@ export const ToolResultDisplay: React.FC<ToolResultDisplayProps> = ({
       return { truncatedResultDisplay: text, hiddenLinesCount: hiddenLines };
     }
 
-    if (Array.isArray(resultDisplay) && !isAlternateBuffer && maxLines) {
+    if (
+      Array.isArray(resultDisplay) &&
+      !isAlternateBuffer &&
+      maxLines !== undefined
+    ) {
       if (resultDisplay.length > maxLines) {
         // We will have a label from MaxSizedBox. Reserve space for it.
         const targetLines = Math.max(1, maxLines - 1);

packages/cli/src/ui/utils/toolLayoutUtils.test.ts

@@ -8,8 +8,6 @@ import { describe, it, expect } from 'vitest';
 import {
   calculateToolContentMaxLines,
   calculateShellMaxLines,
-  TOOL_RESULT_STATIC_HEIGHT,
-  TOOL_RESULT_STANDARD_RESERVED_LINE_COUNT,
 } from './toolLayoutUtils.js';
 import { CoreToolCallStatus } from '@google/gemini-cli-core';
 import {
@@ -36,26 +34,26 @@ describe('toolLayoutUtils', () => {
       expect(result).toBe(10);
     });
 
-    it('caps height to prevent overflow in constrained terminal (Standard mode)', () => {
+    it('returns available space directly in constrained terminal (Standard mode)', () => {
       const availableTerminalHeight = 2; // Very small
       const result = calculateToolContentMaxLines({
         availableTerminalHeight,
         isAlternateBuffer: false,
       });
 
-      // Math.max(0, 2 - 1 - 2) = 0
-      expect(result).toBe(0);
+      // Math.max(0, 2) = 2
+      expect(result).toBe(2);
     });
 
-    it('caps height to prevent overflow in constrained terminal (ASB mode)', () => {
+    it('returns available space directly in constrained terminal (ASB mode)', () => {
       const availableTerminalHeight = 4; // Very small
       const result = calculateToolContentMaxLines({
         availableTerminalHeight,
         isAlternateBuffer: true,
       });
 
-      // Math.max(0, 4 - 1 - 6) = 0
-      expect(result).toBe(0);
+      // Math.max(0, 4) = 4
+      expect(result).toBe(4);
     });
 
     it('returns remaining space if sufficient space exists (Standard mode)', () => {
@@ -65,8 +63,8 @@ describe('toolLayoutUtils', () => {
         isAlternateBuffer: false,
       });
 
-      // Space remaining is 20 - 1 - 2 = 17
-      expect(result).toBe(17);
+      // Math.max(0, 20) = 20
+      expect(result).toBe(20);
     });
 
     it('returns remaining space if sufficient space exists (ASB mode)', () => {
@@ -76,19 +74,8 @@ describe('toolLayoutUtils', () => {
         isAlternateBuffer: true,
       });
 
-      // Space remaining is 20 - 1 - 6 = 13
-      expect(result).toBe(13);
-    });
-
-    it('returns 0 if availableTerminalHeight is <= TOOL_RESULT_STATIC_HEIGHT + reservedLines', () => {
-      const result = calculateToolContentMaxLines({
-        availableTerminalHeight:
-          TOOL_RESULT_STATIC_HEIGHT + TOOL_RESULT_STANDARD_RESERVED_LINE_COUNT,
-        isAlternateBuffer: false,
-      });
-
-      // Cap at 3 - 1 - 2 = 0
-      expect(result).toBe(0);
+      // Math.max(0, 20) = 20
+      expect(result).toBe(20);
     });
   });
 
@@ -129,32 +116,32 @@ describe('toolLayoutUtils', () => {
       expect(result).toBeUndefined();
     });
 
-    it('handles small availableTerminalHeight gracefully to prevent overflow in Standard mode', () => {
+    it('handles small availableTerminalHeight gracefully without overflow in Standard mode', () => {
       const result = calculateShellMaxLines({
         status: CoreToolCallStatus.Executing,
         isAlternateBuffer: false,
         isThisShellFocused: false,
-        availableTerminalHeight: 2, // Too small to subtract 1 + 2
+        availableTerminalHeight: 2,
         constrainHeight: true,
         isExpandable: false,
       });
 
-      // Math.max(0, 2 - 1 - 2) = 0
-      expect(result).toBe(0);
+      // Math.max(0, 2) = 2
+      expect(result).toBe(2);
     });
 
-    it('handles small availableTerminalHeight gracefully to prevent overflow in ASB mode', () => {
+    it('handles small availableTerminalHeight gracefully without overflow in ASB mode', () => {
       const result = calculateShellMaxLines({
         status: CoreToolCallStatus.Executing,
         isAlternateBuffer: true,
         isThisShellFocused: false,
-        availableTerminalHeight: 6, // Too small to subtract 1 + 6
+        availableTerminalHeight: 6,
         constrainHeight: true,
         isExpandable: false,
       });
 
-      // Math.max(0, 6 - 1 - 6) = 0
-      expect(result).toBe(0);
+      // Math.max(0, 6) = 6
+      expect(result).toBe(6);
     });
 
     it('handles negative availableTerminalHeight gracefully', () => {
@@ -180,8 +167,8 @@ describe('toolLayoutUtils', () => {
         isExpandable: false,
       });
 
-      // 30 - 1 (static) - 6 (ASB reserved) = 23
-      expect(result).toBe(23);
+      // 30
+      expect(result).toBe(30);
     });
 
     it('falls back to COMPLETED_SHELL_MAX_LINES for completed shells if space allows', () => {

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

@@ -15,7 +15,6 @@ import { CoreToolCallStatus } from '@google/gemini-cli-core';
  * These MUST be kept in sync between ToolGroupMessage (for overflow detection)
  * and ToolResultDisplay (for actual truncation).
  */
-export const TOOL_RESULT_STATIC_HEIGHT = 1;
 export const TOOL_RESULT_ASB_RESERVED_LINE_COUNT = 6;
 export const TOOL_RESULT_STANDARD_RESERVED_LINE_COUNT = 2;
 export const TOOL_RESULT_MIN_LINES_SHOWN = 2;
@@ -35,9 +34,10 @@ export function calculateToolContentMaxLines(options: {
 }): number | undefined {
   const { availableTerminalHeight, maxLinesLimit } = options;
 
-  let contentHeight = availableTerminalHeight
-    ? Math.max(TOOL_RESULT_STATIC_HEIGHT, availableTerminalHeight)
-    : undefined;
+  let contentHeight =
+    availableTerminalHeight !== undefined
+      ? Math.max(0, availableTerminalHeight)
+      : undefined;
 
   if (maxLinesLimit) {
     contentHeight =
@@ -84,7 +84,7 @@ export function calculateShellMaxLines(options: {
     return isAlternateBuffer ? ACTIVE_SHELL_MAX_LINES : undefined;
   }
 
-  const maxLinesBasedOnHeight = Math.max(1, availableTerminalHeight);
+  const maxLinesBasedOnHeight = Math.max(0, availableTerminalHeight);
 
   // 3. Handle ASB mode focus expansion.
   // We allow a focused shell in ASB mode to take up the full available height,