feat: add Cosmo Router config generation and PubSub support

Creates a new `GenerateCosmoRouterConfig` function to build and 
serialize a Cosmo Router configuration from subgraphs. Implements 
PubSub mechanism for managing schema updates, allowing 
subscription to updates. Adds Subscription resolver and updates 
existing structures to accommodate new functionalities. This 
enhances the system's capabilities for dynamic updates and 
configuration management.

graph/schema.resolvers.go

@@ -119,6 +119,44 @@ func (r *mutationResolver) UpdateSubGraph(ctx context.Context, input model.Input
 	if err != nil {
 		return nil, err
 	}
+
+	// Publish schema update to subscribers
+	go func() {
+		services, lastUpdate := r.Cache.Services(orgId, input.Ref, "")
+		subGraphs := make([]*model.SubGraph, len(services))
+		for i, id := range services {
+			sg, err := r.fetchSubGraph(context.Background(), id)
+			if err != nil {
+				r.Logger.Error("fetch subgraph for update notification", "error", err)
+				continue
+			}
+			subGraphs[i] = &model.SubGraph{
+				ID:        sg.ID.String(),
+				Service:   sg.Service,
+				URL:       sg.Url,
+				WsURL:     sg.WSUrl,
+				Sdl:       sg.Sdl,
+				ChangedBy: sg.ChangedBy,
+				ChangedAt: sg.ChangedAt,
+			}
+		}
+
+		// Generate Cosmo router config
+		cosmoConfig, err := GenerateCosmoRouterConfig(subGraphs)
+		if err != nil {
+			r.Logger.Error("generate cosmo config for update", "error", err)
+			cosmoConfig = "" // Send empty if generation fails
+		}
+
+		// Publish to all subscribers of this ref
+		r.PubSub.Publish(input.Ref, &model.SchemaUpdate{
+			Ref:               input.Ref,
+			ID:                lastUpdate,
+			SubGraphs:         subGraphs,
+			CosmoRouterConfig: &cosmoConfig,
+		})
+	}()
+
 	return r.toGqlSubGraph(subGraph), nil
 }
 
@@ -184,13 +222,74 @@ func (r *queryResolver) Supergraph(ctx context.Context, ref string, isAfter *str
 	}, nil
 }
 
+// SchemaUpdates is the resolver for the schemaUpdates field.
+func (r *subscriptionResolver) SchemaUpdates(ctx context.Context, ref string) (<-chan *model.SchemaUpdate, error) {
+	orgId := middleware.OrganizationFromContext(ctx)
+	_, err := r.apiKeyCanAccessRef(ctx, ref, false)
+	if err != nil {
+		return nil, err
+	}
+
+	// Subscribe to updates for this ref
+	ch := r.PubSub.Subscribe(ref)
+
+	// Send initial state immediately
+	go func() {
+		services, lastUpdate := r.Cache.Services(orgId, ref, "")
+		subGraphs := make([]*model.SubGraph, len(services))
+		for i, id := range services {
+			sg, err := r.fetchSubGraph(ctx, id)
+			if err != nil {
+				r.Logger.Error("fetch subgraph for initial update", "error", err)
+				continue
+			}
+			subGraphs[i] = &model.SubGraph{
+				ID:        sg.ID.String(),
+				Service:   sg.Service,
+				URL:       sg.Url,
+				WsURL:     sg.WSUrl,
+				Sdl:       sg.Sdl,
+				ChangedBy: sg.ChangedBy,
+				ChangedAt: sg.ChangedAt,
+			}
+		}
+
+		// Generate Cosmo router config
+		cosmoConfig, err := GenerateCosmoRouterConfig(subGraphs)
+		if err != nil {
+			r.Logger.Error("generate cosmo config", "error", err)
+			cosmoConfig = "" // Send empty if generation fails
+		}
+
+		// Send initial update
+		ch <- &model.SchemaUpdate{
+			Ref:               ref,
+			ID:                lastUpdate,
+			SubGraphs:         subGraphs,
+			CosmoRouterConfig: &cosmoConfig,
+		}
+	}()
+
+	// Clean up subscription when context is done
+	go func() {
+		<-ctx.Done()
+		r.PubSub.Unsubscribe(ref, ch)
+	}()
+
+	return ch, nil
+}
+
 // Mutation returns generated.MutationResolver implementation.
 func (r *Resolver) Mutation() generated.MutationResolver { return &mutationResolver{r} }
 
 // Query returns generated.QueryResolver implementation.
 func (r *Resolver) Query() generated.QueryResolver { return &queryResolver{r} }
 
+// Subscription returns generated.SubscriptionResolver implementation.
+func (r *Resolver) Subscription() generated.SubscriptionResolver { return &subscriptionResolver{r} }
+
 type (
-	mutationResolver struct{ *Resolver }
-	queryResolver    struct{ *Resolver }
+	mutationResolver     struct{ *Resolver }
+	queryResolver        struct{ *Resolver }
+	subscriptionResolver struct{ *Resolver }
 )