fix(outbounds): preserve stable subscription tags

internal/web/service/outbound_subscription.go

@@ -462,6 +462,13 @@ func (s *OutboundSubscriptionService) recordError(sub *model.OutboundSubscriptio
 // written back into parsed[i]["tag"]. The returned slice holds the assigned tags
 // in order. When tagPrefix is empty a "sub<subID>-" prefix is used for fresh tags.
 func assignStableTags(parsed []link.Outbound, identities []string, prev map[string]string, prevTagByIndex map[int]string, subID int, tagPrefix string) []string {
+	reservedStableTags := map[string]bool{}
+	for i := range parsed {
+		if i < len(identities) && prev[identities[i]] != "" {
+			reservedStableTags[prev[identities[i]]] = true
+		}
+	}
+
 	used := map[string]bool{} // uniqueness within this refresh batch
 	assigned := make([]string, len(parsed))
 	for i := range parsed {
@@ -470,12 +477,14 @@ func assignStableTags(parsed []link.Outbound, identities []string, prev map[stri
 			id = identities[i]
 		}
 		candidate := ""
+		identityTag := ""
 		if old, ok := prev[id]; ok && old != "" {
 			candidate = old
+			identityTag = old
 		}
 		if candidate == "" {
 			// try to reuse by rough positional match from previous fetch (best effort)
-			if old, ok := prevTagByIndex[i]; ok && old != "" {
+			if old, ok := prevTagByIndex[i]; ok && old != "" && !reservedStableTags[old] {
 				candidate = old
 			}
 		}
@@ -493,7 +502,7 @@ func assignStableTags(parsed []link.Outbound, identities []string, prev map[stri
 		}
 		// ensure local uniqueness inside this batch
 		final := candidate
-		for k := 1; used[final]; k++ {
+		for k := 1; used[final] || (reservedStableTags[final] && final != identityTag); k++ {
 			final = fmt.Sprintf("%s-%d", candidate, k)
 		}
 		used[final] = true

internal/web/service/outbound_subscription_test.go

@@ -3,6 +3,7 @@ package service
 import (
 	"bytes"
 	"errors"
+	"slices"
 	"testing"
 
 	"gorm.io/gorm"
@@ -166,12 +167,53 @@ func TestAssignStableTags(t *testing.T) {
 
 	t.Run("falls back to the previous tag at the same position", func(t *testing.T) {
 		parsed := []link.Outbound{{"tag": "JP-Tokyo"}}
-		got := assignStableTags(parsed, []string{"id-new"}, map[string]string{}, map[int]string{0: "sub1-oldpos"}, 1, "")
+		prev := map[string]string{"id-gone": "sub1-oldpos"}
+		got := assignStableTags(parsed, []string{"id-new"}, prev, map[int]string{0: "sub1-oldpos"}, 1, "")
 		if got[0] != "sub1-oldpos" {
 			t.Fatalf("got %q, want sub1-oldpos", got[0])
 		}
 	})
 
+	t.Run("does not let an inserted link steal a stable tag", func(t *testing.T) {
+		parsed := []link.Outbound{{"tag": "Poland"}, {"tag": "NewServer"}, {"tag": "Netherlands"}}
+		prev := map[string]string{
+			"id-poland":      "sub1-poland",
+			"id-netherlands": "sub1-netherlands",
+		}
+		prevTagByIndex := map[int]string{0: "sub1-poland", 1: "sub1-netherlands"}
+
+		got := assignStableTags(parsed, []string{"id-poland", "id-new", "id-netherlands"}, prev, prevTagByIndex, 1, "")
+		want := []string{"sub1-poland", "sub1-newserver", "sub1-netherlands"}
+		if !slices.Equal(got, want) {
+			t.Fatalf("got %v, want %v", got, want)
+		}
+	})
+
+	t.Run("does not let a fresh tag steal a stable tag", func(t *testing.T) {
+		parsed := []link.Outbound{{"tag": "Netherlands"}, {"tag": "Renamed"}}
+		prev := map[string]string{"id-netherlands": "sub1-netherlands"}
+
+		got := assignStableTags(parsed, []string{"id-new", "id-netherlands"}, prev, nil, 1, "")
+		want := []string{"sub1-netherlands-1", "sub1-netherlands"}
+		if !slices.Equal(got, want) {
+			t.Fatalf("got %v, want %v", got, want)
+		}
+	})
+
+	t.Run("skips reserved tags while adding a suffix", func(t *testing.T) {
+		parsed := []link.Outbound{{"tag": "Netherlands"}, {"tag": "First"}, {"tag": "Second"}}
+		prev := map[string]string{
+			"id-first":  "sub1-netherlands",
+			"id-second": "sub1-netherlands-1",
+		}
+
+		got := assignStableTags(parsed, []string{"id-new", "id-first", "id-second"}, prev, nil, 1, "")
+		want := []string{"sub1-netherlands-2", "sub1-netherlands", "sub1-netherlands-1"}
+		if !slices.Equal(got, want) {
+			t.Fatalf("got %v, want %v", got, want)
+		}
+	})
+
 	t.Run("allocates a fresh tag with the default sub<id>- prefix", func(t *testing.T) {
 		parsed := []link.Outbound{{"tag": "Tokyo"}}
 		got := assignStableTags(parsed, []string{"id-x"}, nil, nil, 7, "")