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diff --git a/packages/core/src/utils/systemEncoding.test.ts b/packages/core/src/utils/systemEncoding.test.ts
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+++ b/packages/core/src/utils/systemEncoding.test.ts
@@ -0,0 +1,496 @@
+/**
+ * @license
+ * Copyright 2025 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+import { vi, describe, it, expect, beforeEach, afterEach } from 'vitest';
+import { execSync } from 'child_process';
+import * as os from 'os';
+import { detect as chardetDetect } from 'chardet';
+
+// Mock dependencies
+vi.mock('child_process');
+vi.mock('os');
+vi.mock('chardet');
+
+// Import the functions we want to test after refactoring
+import {
+  getCachedEncodingForBuffer,
+  getSystemEncoding,
+  windowsCodePageToEncoding,
+  detectEncodingFromBuffer,
+  resetEncodingCache,
+} from './systemEncoding.js';
+
+describe('Shell Command Processor - Encoding Functions', () => {
+  let consoleWarnSpy: ReturnType<typeof vi.spyOn>;
+  let mockedExecSync: ReturnType<typeof vi.mocked<typeof execSync>>;
+  let mockedOsPlatform: ReturnType<typeof vi.mocked<() => string>>;
+  let mockedChardetDetect: ReturnType<typeof vi.mocked<typeof chardetDetect>>;
+
+  beforeEach(() => {
+    consoleWarnSpy = vi.spyOn(console, 'warn').mockImplementation(() => {});
+    mockedExecSync = vi.mocked(execSync);
+    mockedOsPlatform = vi.mocked(os.platform);
+    mockedChardetDetect = vi.mocked(chardetDetect);
+
+    // Reset the encoding cache before each test
+    resetEncodingCache();
+
+    // Clear environment variables that might affect tests
+    delete process.env.LC_ALL;
+    delete process.env.LC_CTYPE;
+    delete process.env.LANG;
+  });
+
+  afterEach(() => {
+    vi.restoreAllMocks();
+    resetEncodingCache();
+  });
+
+  describe('windowsCodePageToEncoding', () => {
+    it('should map common Windows code pages correctly', () => {
+      expect(windowsCodePageToEncoding(437)).toBe('cp437');
+      expect(windowsCodePageToEncoding(850)).toBe('cp850');
+      expect(windowsCodePageToEncoding(65001)).toBe('utf-8');
+      expect(windowsCodePageToEncoding(1252)).toBe('windows-1252');
+      expect(windowsCodePageToEncoding(932)).toBe('shift_jis');
+      expect(windowsCodePageToEncoding(936)).toBe('gb2312');
+      expect(windowsCodePageToEncoding(949)).toBe('euc-kr');
+      expect(windowsCodePageToEncoding(950)).toBe('big5');
+      expect(windowsCodePageToEncoding(1200)).toBe('utf-16le');
+      expect(windowsCodePageToEncoding(1201)).toBe('utf-16be');
+    });
+
+    it('should return null for unmapped code pages and warn', () => {
+      expect(windowsCodePageToEncoding(99999)).toBe(null);
+      expect(consoleWarnSpy).toHaveBeenCalledWith(
+        'Unable to determine encoding for windows code page 99999.',
+      );
+    });
+
+    it('should handle all Windows-specific code pages', () => {
+      expect(windowsCodePageToEncoding(874)).toBe('windows-874');
+      expect(windowsCodePageToEncoding(1250)).toBe('windows-1250');
+      expect(windowsCodePageToEncoding(1251)).toBe('windows-1251');
+      expect(windowsCodePageToEncoding(1253)).toBe('windows-1253');
+      expect(windowsCodePageToEncoding(1254)).toBe('windows-1254');
+      expect(windowsCodePageToEncoding(1255)).toBe('windows-1255');
+      expect(windowsCodePageToEncoding(1256)).toBe('windows-1256');
+      expect(windowsCodePageToEncoding(1257)).toBe('windows-1257');
+      expect(windowsCodePageToEncoding(1258)).toBe('windows-1258');
+    });
+  });
+
+  describe('detectEncodingFromBuffer', () => {
+    it('should detect encoding using chardet successfully', () => {
+      const buffer = Buffer.from('test content', 'utf8');
+      mockedChardetDetect.mockReturnValue('UTF-8');
+
+      const result = detectEncodingFromBuffer(buffer);
+      expect(result).toBe('utf-8');
+      expect(mockedChardetDetect).toHaveBeenCalledWith(buffer);
+    });
+
+    it('should handle chardet returning mixed case encoding', () => {
+      const buffer = Buffer.from('test content', 'utf8');
+      mockedChardetDetect.mockReturnValue('ISO-8859-1');
+
+      const result = detectEncodingFromBuffer(buffer);
+      expect(result).toBe('iso-8859-1');
+    });
+
+    it('should return null when chardet fails', () => {
+      const buffer = Buffer.from('test content', 'utf8');
+      mockedChardetDetect.mockImplementation(() => {
+        throw new Error('Detection failed');
+      });
+
+      const result = detectEncodingFromBuffer(buffer);
+      expect(result).toBe(null);
+      expect(consoleWarnSpy).toHaveBeenCalledWith(
+        'Failed to detect encoding with chardet:',
+        expect.any(Error),
+      );
+    });
+
+    it('should return null when chardet returns null', () => {
+      const buffer = Buffer.from('test content', 'utf8');
+      mockedChardetDetect.mockReturnValue(null);
+
+      const result = detectEncodingFromBuffer(buffer);
+      expect(result).toBe(null);
+    });
+
+    it('should return null when chardet returns non-string', () => {
+      const buffer = Buffer.from('test content', 'utf8');
+      mockedChardetDetect.mockReturnValue([
+        'utf-8',
+        'iso-8859-1',
+      ] as unknown as string);
+
+      const result = detectEncodingFromBuffer(buffer);
+      expect(result).toBe(null);
+    });
+  });
+
+  describe('getSystemEncoding - Windows', () => {
+    beforeEach(() => {
+      mockedOsPlatform.mockReturnValue('win32');
+    });
+
+    it('should parse Windows chcp output correctly', () => {
+      mockedExecSync.mockReturnValue('Active code page: 65001');
+
+      const result = getSystemEncoding();
+      expect(result).toBe('utf-8');
+      expect(mockedExecSync).toHaveBeenCalledWith('chcp', { encoding: 'utf8' });
+    });
+
+    it('should handle different chcp output formats', () => {
+      mockedExecSync.mockReturnValue('Current code page: 1252');
+
+      const result = getSystemEncoding();
+      expect(result).toBe('windows-1252');
+    });
+
+    it('should handle chcp output with extra whitespace', () => {
+      mockedExecSync.mockReturnValue('Active code page:   437   ');
+
+      const result = getSystemEncoding();
+      expect(result).toBe('cp437');
+    });
+
+    it('should return null when chcp command fails', () => {
+      mockedExecSync.mockImplementation(() => {
+        throw new Error('Command failed');
+      });
+
+      const result = getSystemEncoding();
+      expect(result).toBe(null);
+      expect(consoleWarnSpy).toHaveBeenCalledWith(
+        expect.stringContaining(
+          "Failed to get Windows code page using 'chcp' command",
+        ),
+      );
+    });
+
+    it('should return null when chcp output cannot be parsed', () => {
+      mockedExecSync.mockReturnValue('Unexpected output format');
+
+      const result = getSystemEncoding();
+      expect(result).toBe(null);
+      expect(consoleWarnSpy).toHaveBeenCalledWith(
+        expect.stringContaining(
+          "Failed to get Windows code page using 'chcp' command",
+        ),
+      );
+    });
+
+    it('should return null when code page is not a number', () => {
+      mockedExecSync.mockReturnValue('Active code page: abc');
+
+      const result = getSystemEncoding();
+      expect(result).toBe(null);
+      expect(consoleWarnSpy).toHaveBeenCalledWith(
+        expect.stringContaining(
+          "Failed to get Windows code page using 'chcp' command",
+        ),
+      );
+    });
+
+    it('should return null when code page maps to null', () => {
+      mockedExecSync.mockReturnValue('Active code page: 99999');
+
+      const result = getSystemEncoding();
+      expect(result).toBe(null);
+      // Should warn about unknown code page from windowsCodePageToEncoding
+      expect(consoleWarnSpy).toHaveBeenCalledWith(
+        'Unable to determine encoding for windows code page 99999.',
+      );
+    });
+  });
+
+  describe('getSystemEncoding - Unix-like', () => {
+    beforeEach(() => {
+      mockedOsPlatform.mockReturnValue('linux');
+    });
+
+    it('should parse locale from LC_ALL environment variable', () => {
+      process.env.LC_ALL = 'en_US.UTF-8';
+
+      const result = getSystemEncoding();
+      expect(result).toBe('utf-8');
+    });
+
+    it('should parse locale from LC_CTYPE when LC_ALL is not set', () => {
+      process.env.LC_CTYPE = 'fr_FR.ISO-8859-1';
+
+      const result = getSystemEncoding();
+      expect(result).toBe('iso-8859-1');
+    });
+
+    it('should parse locale from LANG when LC_ALL and LC_CTYPE are not set', () => {
+      process.env.LANG = 'de_DE.UTF-8';
+
+      const result = getSystemEncoding();
+      expect(result).toBe('utf-8');
+    });
+
+    it('should handle locale charmap command when environment variables are empty', () => {
+      mockedExecSync.mockReturnValue('UTF-8\n');
+
+      const result = getSystemEncoding();
+      expect(result).toBe('utf-8');
+      expect(mockedExecSync).toHaveBeenCalledWith('locale charmap', {
+        encoding: 'utf8',
+      });
+    });
+
+    it('should handle locale charmap with mixed case', () => {
+      mockedExecSync.mockReturnValue('ISO-8859-1\n');
+
+      const result = getSystemEncoding();
+      expect(result).toBe('iso-8859-1');
+    });
+
+    it('should return null when locale charmap fails', () => {
+      mockedExecSync.mockImplementation(() => {
+        throw new Error('Command failed');
+      });
+
+      const result = getSystemEncoding();
+      expect(result).toBe(null);
+      expect(consoleWarnSpy).toHaveBeenCalledWith(
+        'Failed to get locale charmap.',
+      );
+    });
+
+    it('should handle locale without encoding (no dot)', () => {
+      process.env.LANG = 'C';
+
+      const result = getSystemEncoding();
+      expect(result).toBe('c');
+    });
+
+    it('should handle empty locale environment variables', () => {
+      process.env.LC_ALL = '';
+      process.env.LC_CTYPE = '';
+      process.env.LANG = '';
+      mockedExecSync.mockReturnValue('UTF-8');
+
+      const result = getSystemEncoding();
+      expect(result).toBe('utf-8');
+    });
+
+    it('should return locale as-is when locale format has no dot', () => {
+      process.env.LANG = 'invalid_format';
+
+      const result = getSystemEncoding();
+      expect(result).toBe('invalid_format');
+    });
+
+    it('should prioritize LC_ALL over other environment variables', () => {
+      process.env.LC_ALL = 'en_US.UTF-8';
+      process.env.LC_CTYPE = 'fr_FR.ISO-8859-1';
+      process.env.LANG = 'de_DE.CP1252';
+
+      const result = getSystemEncoding();
+      expect(result).toBe('utf-8');
+    });
+
+    it('should prioritize LC_CTYPE over LANG', () => {
+      process.env.LC_CTYPE = 'fr_FR.ISO-8859-1';
+      process.env.LANG = 'de_DE.CP1252';
+
+      const result = getSystemEncoding();
+      expect(result).toBe('iso-8859-1');
+    });
+  });
+
+  describe('getEncodingForBuffer', () => {
+    beforeEach(() => {
+      mockedOsPlatform.mockReturnValue('linux');
+    });
+
+    it('should use cached system encoding on subsequent calls', () => {
+      process.env.LANG = 'en_US.UTF-8';
+      const buffer = Buffer.from('test');
+
+      // First call
+      const result1 = getCachedEncodingForBuffer(buffer);
+      expect(result1).toBe('utf-8');
+
+      // Change environment (should not affect cached result)
+      process.env.LANG = 'fr_FR.ISO-8859-1';
+
+      // Second call should use cached value
+      const result2 = getCachedEncodingForBuffer(buffer);
+      expect(result2).toBe('utf-8');
+    });
+
+    it('should fall back to buffer detection when system encoding fails', () => {
+      // No environment variables set
+      mockedExecSync.mockImplementation(() => {
+        throw new Error('locale command failed');
+      });
+
+      const buffer = Buffer.from('test');
+      mockedChardetDetect.mockReturnValue('ISO-8859-1');
+
+      const result = getCachedEncodingForBuffer(buffer);
+      expect(result).toBe('iso-8859-1');
+      expect(mockedChardetDetect).toHaveBeenCalledWith(buffer);
+    });
+
+    it('should fall back to utf-8 when both system and buffer detection fail', () => {
+      // System encoding fails
+      mockedExecSync.mockImplementation(() => {
+        throw new Error('locale command failed');
+      });
+
+      // Buffer detection fails
+      mockedChardetDetect.mockImplementation(() => {
+        throw new Error('chardet failed');
+      });
+
+      const buffer = Buffer.from('test');
+      const result = getCachedEncodingForBuffer(buffer);
+      expect(result).toBe('utf-8');
+    });
+
+    it('should not cache buffer detection results', () => {
+      // System encoding fails initially
+      mockedExecSync.mockImplementation(() => {
+        throw new Error('locale command failed');
+      });
+
+      const buffer1 = Buffer.from('test1');
+      const buffer2 = Buffer.from('test2');
+
+      mockedChardetDetect
+        .mockReturnValueOnce('ISO-8859-1')
+        .mockReturnValueOnce('UTF-16');
+
+      const result1 = getCachedEncodingForBuffer(buffer1);
+      const result2 = getCachedEncodingForBuffer(buffer2);
+
+      expect(result1).toBe('iso-8859-1');
+      expect(result2).toBe('utf-16');
+      expect(mockedChardetDetect).toHaveBeenCalledTimes(2);
+    });
+
+    it('should handle Windows system encoding', () => {
+      mockedOsPlatform.mockReturnValue('win32');
+      mockedExecSync.mockReturnValue('Active code page: 1252');
+
+      const buffer = Buffer.from('test');
+      const result = getCachedEncodingForBuffer(buffer);
+
+      expect(result).toBe('windows-1252');
+    });
+
+    it('should cache null system encoding result', () => {
+      // Reset the cache specifically for this test
+      resetEncodingCache();
+
+      // Ensure we're on Unix-like for this test
+      mockedOsPlatform.mockReturnValue('linux');
+
+      // System encoding detection returns null
+      mockedExecSync.mockImplementation(() => {
+        throw new Error('locale command failed');
+      });
+
+      const buffer1 = Buffer.from('test1');
+      const buffer2 = Buffer.from('test2');
+
+      mockedChardetDetect
+        .mockReturnValueOnce('ISO-8859-1')
+        .mockReturnValueOnce('UTF-16');
+
+      // Clear any previous calls from beforeEach setup or previous tests
+      mockedExecSync.mockClear();
+
+      const result1 = getCachedEncodingForBuffer(buffer1);
+      const result2 = getCachedEncodingForBuffer(buffer2);
+
+      // Should call execSync only once due to caching (null result is cached)
+      expect(mockedExecSync).toHaveBeenCalledTimes(1);
+      expect(result1).toBe('iso-8859-1');
+      expect(result2).toBe('utf-16');
+
+      // Call a third time to verify cache is still used
+      const buffer3 = Buffer.from('test3');
+      mockedChardetDetect.mockReturnValueOnce('UTF-32');
+      const result3 = getCachedEncodingForBuffer(buffer3);
+
+      // Still should be only one call to execSync
+      expect(mockedExecSync).toHaveBeenCalledTimes(1);
+      expect(result3).toBe('utf-32');
+    });
+  });
+
+  describe('Cross-platform behavior', () => {
+    it('should work correctly on macOS', () => {
+      mockedOsPlatform.mockReturnValue('darwin');
+      process.env.LANG = 'en_US.UTF-8';
+
+      const result = getSystemEncoding();
+      expect(result).toBe('utf-8');
+    });
+
+    it('should work correctly on other Unix-like systems', () => {
+      mockedOsPlatform.mockReturnValue('freebsd');
+      process.env.LANG = 'en_US.UTF-8';
+
+      const result = getSystemEncoding();
+      expect(result).toBe('utf-8');
+    });
+
+    it('should handle unknown platforms as Unix-like', () => {
+      mockedOsPlatform.mockReturnValue('unknown' as NodeJS.Platform);
+      process.env.LANG = 'en_US.UTF-8';
+
+      const result = getSystemEncoding();
+      expect(result).toBe('utf-8');
+    });
+  });
+
+  describe('Edge cases and error handling', () => {
+    it('should handle empty buffer gracefully', () => {
+      mockedOsPlatform.mockReturnValue('linux');
+      process.env.LANG = 'en_US.UTF-8';
+
+      const buffer = Buffer.alloc(0);
+      const result = getCachedEncodingForBuffer(buffer);
+      expect(result).toBe('utf-8');
+    });
+
+    it('should handle very large buffers', () => {
+      mockedOsPlatform.mockReturnValue('linux');
+      process.env.LANG = 'en_US.UTF-8';
+
+      const buffer = Buffer.alloc(1024 * 1024, 'a');
+      const result = getCachedEncodingForBuffer(buffer);
+      expect(result).toBe('utf-8');
+    });
+
+    it('should handle Unicode content', () => {
+      mockedOsPlatform.mockReturnValue('linux');
+      const unicodeText = '你好世界 🌍 ñoño';
+
+      // System encoding fails
+      mockedExecSync.mockImplementation(() => {
+        throw new Error('locale command failed');
+      });
+
+      mockedChardetDetect.mockReturnValue('UTF-8');
+
+      const buffer = Buffer.from(unicodeText, 'utf8');
+      const result = getCachedEncodingForBuffer(buffer);
+      expect(result).toBe('utf-8');
+    });
+  });
+});