fix: handle undefined content in WriteToFileTool handlePartial method

- Fix ENOENT error when creating new files in Code mode
- Ensure diffViewProvider.open is called even when content is undefined in partial blocks
- Update test to reflect correct behavior for file creation workflow
- Fixes #9611

src/core/tools/WriteToFileTool.ts

@@ -330,11 +330,11 @@ export class WriteToFileTool extends BaseTool<"write_to_file"> {
 		const partialMessage = JSON.stringify(sharedMessageProps)
 		await task.ask("tool", partialMessage, block.partial).catch(() => {})
 
-		if (newContent) {
-			if (!task.diffViewProvider.isEditing) {
-				await task.diffViewProvider.open(relPath)
-			}
+		if (!task.diffViewProvider.isEditing) {
+			await task.diffViewProvider.open(relPath)
+		}
 
+		if (newContent) {
 			await task.diffViewProvider.update(
 				everyLineHasLineNumbers(newContent) ? stripLineNumbers(newContent) : newContent,
 				false,

src/core/tools/__tests__/writeToFileTool.spec.ts

@@ -354,10 +354,13 @@ describe("writeToFileTool", () => {
 			expect(mockCline.diffViewProvider.open).not.toHaveBeenCalled()
 		})
 
-		it("returns early when content is undefined in partial block", async () => {
+		it("opens file even when content is undefined in partial block", async () => {
 			await executeWriteFileTool({ content: undefined }, { isPartial: true })
 
-			expect(mockCline.diffViewProvider.open).not.toHaveBeenCalled()
+			// File should be opened to create it, even if content is not yet available
+			expect(mockCline.diffViewProvider.open).toHaveBeenCalledWith(testFilePath)
+			// But update should not be called since there's no content
+			expect(mockCline.diffViewProvider.update).not.toHaveBeenCalled()
 		})
 
 		it("streams content updates during partial execution", async () => {