fix(core): resolve Windows line ending and path separation bugs across CLI (#21068)

packages/core/src/tools/read-many-files.test.ts

@@ -776,7 +776,7 @@ Content of file[1]
 
       // Mock to track concurrent vs sequential execution
       detectFileTypeSpy.mockImplementation(async (filePath: string) => {
-        const fileName = filePath.split('/').pop() || '';
+        const fileName = path.basename(filePath);
         executionOrder.push(`start:${fileName}`);
 
         // Add delay to make timing differences visible

packages/core/src/utils/fileUtils.ts

@@ -8,7 +8,6 @@ import fs from 'node:fs';
 import fsPromises from 'node:fs/promises';
 import path from 'node:path';
 import type { PartUnion } from '@google/genai';
-
 import mime from 'mime/lite';
 import type { FileSystemService } from '../services/fileSystemService.js';
 import { ToolErrorType } from '../tools/tool-error.js';
@@ -473,7 +472,7 @@ export async function processSingleFileContent(
       case 'text': {
         // Use BOM-aware reader to avoid leaving a BOM character in content and to support UTF-16/32 transparently
         const content = await readFileWithEncoding(filePath);
-        const lines = content.split('\n');
+        const lines = content.split(/\r?\n/);
         const originalLineCount = lines.length;
 
         let sliceStart = 0;