refactor(plugins): validate scheduler capability at load time

Move scheduler capability check from runtime (when callback fires) to
load-time validation in ValidateWithCapabilities. This ensures plugins
declaring the scheduler permission must export the nd_scheduler_callback
function, failing fast with a clear error instead of silently skipping
callbacks at runtime.

plugins/host_scheduler.go

@@ -188,12 +188,6 @@ func (s *schedulerServiceImpl) invokeCallback(ctx context.Context, scheduleID st
 		return
 	}
 
-	// Check if plugin has the scheduler capability
-	if !hasCapability(instance.capabilities, CapabilityScheduler) {
-		log.Warn(ctx, "Plugin does not have scheduler capability", "plugin", s.pluginName, "scheduleID", scheduleID)
-		return
-	}
-
 	// Prepare callback input
 	input := capabilities.SchedulerCallbackRequest{
 		ScheduleID:  scheduleID,

plugins/manifest.go

@@ -64,6 +64,14 @@ func ValidateWithCapabilities(m *Manifest, capabilities []Capability) error {
 			return fmt.Errorf("scrobbler capability requires 'users' permission to be declared in manifest")
 		}
 	}
+
+	// Scheduler permission requires SchedulerCallback capability
+	if m.Permissions != nil && m.Permissions.Scheduler != nil {
+		if !hasCapability(capabilities, CapabilityScheduler) {
+			return fmt.Errorf("'scheduler' permission requires plugin to export '%s' function", FuncSchedulerCallback)
+		}
+	}
+
 	return nil
 }