fix(filesystem): add guidance for failed edit matches

src/filesystem/__tests__/lib.test.ts

@@ -516,7 +516,9 @@ describe('Lib Functions', () => {
         ];
 
         await expect(applyFileEdits('/test/file.txt', edits, false))
-          .rejects.toThrow('Could not find exact match for edit');
+          .rejects.toThrow(
+            'Use read_file to inspect the exact current content, then retry with oldText copied from the file'
+          );
       });
 
       it('handles complex multi-line edits with indentation', async () => {

src/filesystem/lib.ts

@@ -248,7 +248,11 @@ export async function applyFileEdits(
     }
 
     if (!matchFound) {
-      throw new Error(`Could not find exact match for edit:\n${edit.oldText}`);
+      throw new Error(
+        `Could not find exact match for edit:\n${edit.oldText}\n\n` +
+        `This usually means the requested text differs from the file content in whitespace, indentation, or line endings. ` +
+        `Use read_file to inspect the exact current content, then retry with oldText copied from the file.`
+      );
     }
   }