wip: directory/file move name conflict check

packages/convex/model/error.ts

@@ -1,6 +1,7 @@
 import { ConvexError } from "convex/values"
 
 export enum Code {
+	Conflict = "Conflict",
 	DirectoryExists = "DirectoryExists",
 	DirectoryNotFound = "DirectoryNotFound",
 	FileExists = "FileExists",
@@ -8,13 +9,13 @@ export enum Code {
 	Unauthenticated = "Unauthenticated",
 }
 
-export type ApplicationError = ConvexError<{ code: Code; message: string }>
+export type ApplicationError = ConvexError<{ code: Code; message?: string }>
 
 export function isApplicationError(error: unknown): error is ApplicationError {
 	return error instanceof ConvexError && "code" in error.data
 }
 
-export function create(code: Code, message?: string) {
+export function create(code: Code, message?: string): ApplicationError {
 	return new ConvexError({
 		code,
 		message: