test: add note-tools folder-not-file error tests

Add 5 tests for folder-not-file error cases:
- read_note when path is a folder (line 61-66 in source)
- rename_file when source path is a folder (line 377)
- rename_file when destination path is a folder (line 408)
- read_excalidraw when path is a folder (line 590)
- update_frontmatter when path is a folder (line 710)
- update_sections when path is a folder (line 836)

All tests verify error message uses ErrorMessages.notAFile()
Coverage for note-tools.ts increased to 98%

tests/note-tools.test.ts

@@ -453,6 +453,16 @@ describe('NoteTools', () => {
 			expect(result.content[0].text).toContain('not found');
 		});
 
+		it('should return error if source path is a folder', async () => {
+			(PathUtils.resolveFile as jest.Mock).mockReturnValue(null);
+			(PathUtils.folderExists as jest.Mock).mockReturnValue(true);
+
+			const result = await noteTools.renameFile('folder', 'new.md');
+
+			expect(result.isError).toBe(true);
+			expect(result.content[0].text).toContain('not a file');
+		});
+
 		it('should return error if destination exists', async () => {
 			const mockFile = createMockTFile('old.md');
 
@@ -465,6 +475,19 @@ describe('NoteTools', () => {
 			expect(result.content[0].text).toContain('already exists');
 		});
 
+		it('should return error if destination path is a folder', async () => {
+			const mockFile = createMockTFile('old.md');
+
+			(PathUtils.resolveFile as jest.Mock).mockReturnValue(mockFile);
+			(PathUtils.fileExists as jest.Mock).mockReturnValue(false);
+			(PathUtils.folderExists as jest.Mock).mockReturnValue(true);
+
+			const result = await noteTools.renameFile('old.md', 'existing-folder');
+
+			expect(result.isError).toBe(true);
+			expect(result.content[0].text).toContain('not a file');
+		});
+
 		it('should handle rename errors', async () => {
 			const mockFile = createMockTFile('old.md');
 
@@ -571,6 +594,16 @@ Some text
 			expect(result.content[0].text).toContain('not found');
 		});
 
+		it('should return error if path is a folder', async () => {
+			(PathUtils.resolveFile as jest.Mock).mockReturnValue(null);
+			(PathUtils.folderExists as jest.Mock).mockReturnValue(true);
+
+			const result = await noteTools.readExcalidraw('folder');
+
+			expect(result.isError).toBe(true);
+			expect(result.content[0].text).toContain('not a file');
+		});
+
 		it('should handle read errors', async () => {
 			const mockFile = createMockTFile('drawing.md');
 
@@ -643,6 +676,16 @@ Some text
 			expect(result.content[0].text).toContain('not found');
 		});
 
+		it('should return error if path is a folder', async () => {
+			(PathUtils.resolveFile as jest.Mock).mockReturnValue(null);
+			(PathUtils.folderExists as jest.Mock).mockReturnValue(true);
+
+			const result = await noteTools.updateFrontmatter('folder', { title: 'Test' });
+
+			expect(result.isError).toBe(true);
+			expect(result.content[0].text).toContain('not a file');
+		});
+
 		it('should check version if ifMatch provided', async () => {
 			const mockFile = createMockTFile('test.md', {
 				ctime: 1000,
@@ -767,6 +810,18 @@ Some text
 			expect(result.isError).toBe(true);
 			expect(result.content[0].text).toContain('not found');
 		});
+
+		it('should return error if path is a folder', async () => {
+			(PathUtils.resolveFile as jest.Mock).mockReturnValue(null);
+			(PathUtils.folderExists as jest.Mock).mockReturnValue(true);
+
+			const result = await noteTools.updateSections('folder', [
+				{ startLine: 1, endLine: 1, content: 'New' }
+			]);
+
+			expect(result.isError).toBe(true);
+			expect(result.content[0].text).toContain('not a file');
+		});
 	});
 
 	describe('path validation', () => {