feat: support merging multiple subscriptions

internal/model/subscription.go

@@ -4,6 +4,7 @@ package model
 import (
 	"fmt"
 	"path/filepath"
+	"sort"
 )
 
 // SubscriptionStatus mirrors Python's SubscriptionStatus(str, Enum).
@@ -56,29 +57,40 @@ func NewSubscriptionsData() *SubscriptionsData {
 	return &SubscriptionsData{Subscriptions: make(map[string]*Subscription)}
 }
 
-// GetActiveSubscription returns the currently active subscription, if any.
-func (d *SubscriptionsData) GetActiveSubscription() *Subscription {
+// GetActiveSubscriptions returns every subscription currently marked active,
+// sorted by name for deterministic ordering. Multiple subscriptions may be
+// active simultaneously — config apply merges all of them (see
+// internal/corecfg), prefixing each proxy's name with its source
+// subscription's name to avoid collisions.
+func (d *SubscriptionsData) GetActiveSubscriptions() []*Subscription {
+	var actives []*Subscription
 	for _, sub := range d.Subscriptions {
 		if sub.Status == StatusActive {
-			return sub
+			actives = append(actives, sub)
 		}
 	}
-	return nil
+	sort.Slice(actives, func(i, j int) bool { return actives[i].Name < actives[j].Name })
+	return actives
 }
 
-// SetActive marks name as active and deactivates all others. Returns false if
-// name does not exist.
+// SetActive marks name as active, in addition to any other subscriptions
+// already active. Returns false if name does not exist.
 func (d *SubscriptionsData) SetActive(name string) bool {
-	if _, ok := d.Subscriptions[name]; !ok {
+	sub, ok := d.Subscriptions[name]
+	if !ok {
 		return false
 	}
-	for subName, sub := range d.Subscriptions {
-		if subName == name {
-			sub.Status = StatusActive
-		} else {
-			sub.Status = StatusInactive
-		}
+	sub.Status = StatusActive
+	return true
+}
+
+// SetInactive marks name as inactive. Returns false if name does not exist.
+func (d *SubscriptionsData) SetInactive(name string) bool {
+	sub, ok := d.Subscriptions[name]
+	if !ok {
+		return false
 	}
+	sub.Status = StatusInactive
 	return true
 }