fix: properly report tool errors in telemetry (#5688)

Co-authored-by: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com>

packages/core/src/utils/fileUtils.ts

@@ -195,10 +195,18 @@ export async function detectFileType(
   return 'text';
 }
 
+export enum FileErrorType {
+  FILE_NOT_FOUND = 'FILE_NOT_FOUND',
+  IS_DIRECTORY = 'IS_DIRECTORY',
+  FILE_TOO_LARGE = 'FILE_TOO_LARGE',
+  READ_ERROR = 'READ_ERROR',
+}
+
 export interface ProcessedFileReadResult {
   llmContent: PartUnion; // string for text, Part for image/pdf/unreadable binary
   returnDisplay: string;
   error?: string; // Optional error message for the LLM if file processing failed
+  errorType?: FileErrorType; // Structured error type using enum
   isTruncated?: boolean; // For text files, indicates if content was truncated
   originalLineCount?: number; // For text files
   linesShown?: [number, number]; // For text files [startLine, endLine] (1-based for display)
@@ -225,6 +233,7 @@ export async function processSingleFileContent(
         llmContent: '',
         returnDisplay: 'File not found.',
         error: `File not found: ${filePath}`,
+        errorType: FileErrorType.FILE_NOT_FOUND,
       };
     }
     const stats = await fs.promises.stat(filePath);
@@ -233,6 +242,7 @@ export async function processSingleFileContent(
         llmContent: '',
         returnDisplay: 'Path is a directory.',
         error: `Path is a directory, not a file: ${filePath}`,
+        errorType: FileErrorType.IS_DIRECTORY,
       };
     }