undo: simplify the interface

include/clap/ext/draft/undo.h

@@ -41,11 +41,6 @@ extern "C" {
 /// and maybe an easier experience for the user because there's a single undo context versus one
 /// for the host and one for each plugin instance.
 
-enum clap_undo_context_flags {
-   // While the host is within a change, it is impossible to perform undo or redo.
-   CLAP_UNDO_IS_WITHIN_CHANGE = 1 << 0,
-};
-
 enum clap_undo_delta_properties_flags {
    // If not set, then all clap_undo_delta_properties's attributes become irrelevant.
    // If set, then the plugin will provide deltas in host->change_made().
@@ -102,6 +97,17 @@ typedef struct clap_plugin_undo {
                                     uint64_t             flags,
                                     const char          *undo_name,
                                     const char          *redo_name);
+
+   // if can_* is false then it invalidates the corresponding name.
+   // [main-thread]
+   void (CLAP_ABI *set_can_undo)(const clap_plugin_t *plugin, bool can_undo);
+   void (CLAP_ABI *set_can_redo)(const clap_plugin_t *plugin, bool can_redo);
+
+   // name: null terminated string if an redo/undo step exists, null otherwise.
+   // [main-thread]
+   void (CLAP_ABI *set_undo_name)(const clap_plugin_t *plugin, const char *name);
+   void (CLAP_ABI *set_redo_name)(const clap_plugin_t *plugin, const char *name);
+
 } clap_plugin_undo_t;
 
 typedef struct clap_host_undo {