Route document workflow prompts through app core

src/app_core/document_session.h

@@ -27,6 +27,12 @@ enum class DocumentSaveDecision {
     save_version,
 };
 
+enum class DocumentWorkflowDecision {
+    unavailable,
+    continue_now,
+    prompt_save_before_continue,
+};
+
 [[nodiscard]] constexpr ProjectOpenDecision plan_project_open(bool has_unsaved_changes) noexcept
 {
     return has_unsaved_changes
@@ -78,4 +84,17 @@ enum class DocumentSaveDecision {
     return DocumentSaveDecision::no_op;
 }
 
+[[nodiscard]] constexpr DocumentWorkflowDecision plan_document_workflow(
+    bool has_canvas,
+    bool has_unsaved_changes) noexcept
+{
+    if (!has_canvas) {
+        return DocumentWorkflowDecision::unavailable;
+    }
+
+    return has_unsaved_changes
+        ? DocumentWorkflowDecision::prompt_save_before_continue
+        : DocumentWorkflowDecision::continue_now;
+}
+
 }