fix: guard optional message field in showMessageBox catch handler

Add optional chaining to options.message?.length in the catch handler
and update the messageLength schema to NullOr(Schema.Number) for
consistency with titleLength and detailLength. Previously, if message
was omitted from MessageBoxOptions and the dialog promise rejected,
accessing .length on undefined would throw a TypeError inside catch,
bypassing the typed ElectronDialogShowMessageBoxError.

Author: cursoragent

apps/desktop/src/electron/ElectronDialog.ts

@@ -42,7 +42,7 @@ export class ElectronDialogShowMessageBoxError extends Schema.TaggedErrorClass<E
   {
     type: Schema.NullOr(Schema.Literals(["none", "info", "error", "question", "warning"])),
     titleLength: Schema.NullOr(Schema.Number),
-    messageLength: Schema.Number,
+    messageLength: Schema.NullOr(Schema.Number),
     detailLength: Schema.NullOr(Schema.Number),
     buttonCount: Schema.Number,
     cause: Schema.Defect(),
@@ -177,7 +177,7 @@ export const make = ElectronDialog.of({
         new ElectronDialogShowMessageBoxError({
           type: options.type ?? null,
           titleLength: options.title?.length ?? null,
-          messageLength: options.message.length,
+          messageLength: options.message?.length ?? null,
           detailLength: options.detail?.length ?? null,
           buttonCount: options.buttons?.length ?? 0,
           cause,