feat: 添加 GBK 编码自动检测支持，文件读写工具透明处理非 UTF-8 文件

新增 encoding.ts 核心模块实现三层编码检测（BOM → UTF-8 fatal → GBK 回退），
改造同步/异步读取路径和写入路径，使 FileReadTool/FileEditTool/FileWriteTool
能正确处理 GBK 编码文件。包含完整单元测试和 spec 文档。

Co-Authored-By: glm-5-turbo <zai-org@claude-code-best.win>

packages/builtin-tools/src/tools/BashTool/BashTool.tsx

@@ -29,6 +29,7 @@ import { extractClaudeCodeHints } from 'src/utils/claudeCodeHints.js';
 import { detectCodeIndexingFromCommand } from 'src/utils/codeIndexing.js';
 import { isEnvTruthy } from 'src/utils/envUtils.js';
 import { isENOENT, ShellError } from 'src/utils/errors.js';
+import { decodeBuffer } from 'src/utils/encoding.js';
 import { detectFileEncoding, detectLineEndings, getFileModificationTime, writeTextContent } from 'src/utils/file.js';
 import { fileHistoryEnabled, fileHistoryTrackEdit } from 'src/utils/fileHistory.js';
 import { truncate } from 'src/utils/format.js';
@@ -511,7 +512,8 @@ async function applySedEdit(
   const encoding = detectFileEncoding(absoluteFilePath);
   let originalContent: string;
   try {
-    originalContent = await fs.readFile(absoluteFilePath, { encoding });
+    const rawBuffer = await fs.readFileBytes(absoluteFilePath);
+    originalContent = decodeBuffer(rawBuffer, encoding);
   } catch (e) {
     if (isENOENT(e)) {
       return {

packages/builtin-tools/src/tools/FileEditTool/FileEditTool.ts

@@ -34,6 +34,11 @@ import {
   type LineEndingType,
   readFileSyncWithMetadata,
 } from 'src/utils/fileRead.js'
+import {
+  detectEncoding,
+  decodeBuffer,
+  type FileEncoding,
+} from 'src/utils/encoding.js'
 import { formatFileSize } from 'src/utils/format.js'
 import { getFsImplementation } from 'src/utils/fsOperations.js'
 import { fetchSingleFileGitDiff, type ToolUseDiff } from 'src/utils/gitDiff.js'
@@ -202,13 +207,8 @@ export const FileEditTool = buildTool({
     let fileContent: string | null
     try {
       const fileBuffer = await fs.readFileBytes(fullFilePath)
-      const encoding: BufferEncoding =
-        fileBuffer.length >= 2 &&
-        fileBuffer[0] === 0xff &&
-        fileBuffer[1] === 0xfe
-          ? 'utf16le'
-          : 'utf8'
-      fileContent = fileBuffer.toString(encoding).replaceAll('\r\n', '\n')
+      const encoding: FileEncoding = detectEncoding(fileBuffer)
+      fileContent = decodeBuffer(fileBuffer, encoding).replaceAll('\r\n', '\n')
     } catch (e) {
       if (isENOENT(e)) {
         fileContent = null
@@ -584,7 +584,7 @@ export const FileEditTool = buildTool({
 function readFileForEdit(absoluteFilePath: string): {
   content: string
   fileExists: boolean
-  encoding: BufferEncoding
+  encoding: FileEncoding
   lineEndings: LineEndingType
 } {
   try {