feat: preserve EOL in files (#16087)

Co-authored-by: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com>
Co-authored-by: Adib234 <30782825+Adib234@users.noreply.github.com>
Co-authored-by: Jack Wotherspoon <jackwoth@google.com>

packages/core/src/utils/textUtils.ts

@@ -54,6 +54,17 @@ export function isBinary(
   return false;
 }
 
+/**
+ * Detects the line ending style of a string.
+ * @param content The string content to analyze.
+ * @returns '\r\n' for Windows-style, '\n' for Unix-style.
+ */
+export function detectLineEnding(content: string): '\r\n' | '\n' {
+  // If a Carriage Return is found, assume Windows-style endings.
+  // This is a simple but effective heuristic.
+  return content.includes('\r\n') ? '\r\n' : '\n';
+}
+
 /**
  * Truncates a string to a maximum length, appending a suffix if truncated.
  * @param str The string to truncate.