Plugin load errors: Add more well-known errors (#85960)

pkg/plugins/manager/pipeline/initialization/steps.go

@@ -79,8 +79,11 @@ func newBackendProcessStarter(processManager process.Manager) *BackendClientStar
 // Start will start the backend plugin process.
 func (b *BackendClientStarter) Start(ctx context.Context, p *plugins.Plugin) (*plugins.Plugin, error) {
 	if err := b.processManager.Start(ctx, p); err != nil {
-		b.log.Error("Could not start plugin", "pluginId", p.ID, "error", err)
-		return nil, err
+		b.log.Error("Could not start plugin backend", "pluginId", p.ID, "error", err)
+		return nil, (&plugins.Error{
+			PluginID:  p.ID,
+			ErrorCode: plugins.ErrorCodeFailedBackendStart,
+		}).WithMessage(err.Error())
 	}
 	return p, nil
 }

pkg/plugins/manager/pipeline/validation/steps.go

@@ -106,7 +106,10 @@ func (a *AngularDetector) Validate(ctx context.Context, p *plugins.Plugin) error
 		// Do not initialize plugins if they're using Angular and Angular support is disabled
 		if p.Angular.Detected && !a.cfg.AngularSupportEnabled {
 			a.log.Error("Refusing to initialize plugin because it's using Angular, which has been disabled", "pluginId", p.ID)
-			return errors.New("angular plugins are not supported")
+			return (&plugins.Error{
+				PluginID:  p.ID,
+				ErrorCode: plugins.ErrorAngular,
+			}).WithMessage("angular plugins are not supported")
 		}
 	}
 	p.Angular.HideDeprecation = slices.Contains(a.cfg.HideAngularDeprecation, p.ID)