[management] Prevent deleting groups referenced by agent network budget rules (#7450)

`validateDeleteGroup` already refuses to delete a group that is still used by routes, policies, nameservers, setup keys, users, network routers, reverse proxy services, and agent network policies. Account-level agent network budget rules also store group IDs in `TargetGroups`, but that check was missing.

Deleting such a group left a dangling ID on the budget rule. `budgetRuleApplies` then never matched callers by group, so the spend cap silently stopped applying.

This adds `isGroupLinkedToAgentNetworkBudgetRule` and uses it in `validateDeleteGroup`, matching the existing helpers.

management/server/group.go

@@ -774,6 +774,14 @@ func validateDeleteGroup(ctx context.Context, transaction store.Store, group *ty
 		return &GroupLinkError{"agent network policy", linkedPolicy.Name}
 	}
 
+	isLinked, linkedRule, err := isGroupLinkedToAgentNetworkBudgetRule(ctx, transaction, group.AccountID, group.ID)
+	if err != nil {
+		return status.Errorf(status.Internal, "failed to check agent network budget rules")
+	}
+	if isLinked {
+		return &GroupLinkError{"agent network budget rule", linkedRule.Name}
+	}
+
 	return checkGroupLinkedToSettings(ctx, transaction, group)
 }
 
@@ -945,6 +953,26 @@ func isGroupLinkedToAgentNetworkPolicy(ctx context.Context, transaction store.St
 	return false, nil
 }
 
+// isGroupLinkedToAgentNetworkBudgetRule checks if a group is a target of any
+// account-level agent network budget rule.
+func isGroupLinkedToAgentNetworkBudgetRule(ctx context.Context, transaction store.Store, accountID string, groupID string) (bool, *agentNetworkTypes.AccountBudgetRule, error) {
+	rules, err := transaction.GetAccountAgentNetworkBudgetRules(ctx, store.LockingStrengthNone, accountID)
+	if err != nil {
+		log.WithContext(ctx).Errorf("error retrieving agent network budget rules while checking group linkage: %v", err)
+		return false, nil, err
+	}
+
+	for _, rule := range rules {
+		if rule == nil {
+			continue
+		}
+		if slices.Contains(rule.TargetGroups, groupID) {
+			return true, rule, nil
+		}
+	}
+	return false, nil, nil
+}
+
 // areGroupChangesAffectPeers checks if any changes to the specified groups will affect peers.
 // It fetches each collection once and checks all groupIDs against them in memory.
 func areGroupChangesAffectPeers(ctx context.Context, transaction store.Store, accountID string, groupIDs []string) (bool, error) {

management/server/group_test.go

@@ -132,6 +132,11 @@ func TestDefaultAccountManager_DeleteGroup(t *testing.T) {
 			"grp-for-agent-network-policy",
 			"agent network policy",
 		},
+		{
+			"agent network budget rule",
+			"grp-for-agent-network-budget-rule",
+			"agent network budget rule",
+		},
 		{
 			"reverse proxy private service access group",
 			"grp-for-rp-private",
@@ -152,6 +157,16 @@ func TestDefaultAccountManager_DeleteGroup(t *testing.T) {
 				return
 			}
 
+			group, getErr := am.GetGroup(context.Background(), account.Id, testCase.groupID, groupAdminUserID)
+			if getErr != nil {
+				t.Errorf("group %s should still exist after failed deletion: %s", testCase.groupID, getErr)
+				return
+			}
+			if group == nil {
+				t.Errorf("group %s was deleted despite the failed deletion", testCase.groupID)
+				return
+			}
+
 			var sErr *status.Error
 			if errors.As(err, &sErr) {
 				if sErr.Message != testCase.expectedReason {
@@ -240,6 +255,12 @@ func TestDefaultAccountManager_DeleteGroups(t *testing.T) {
 			groupIDs:        []string{"grp-for-agent-network-policy"},
 			expectedReasons: []string{"agent network policy"},
 		},
+		{
+			name:               "agent network budget rule",
+			groupIDs:           []string{"grp-for-agent-network-budget-rule"},
+			expectedReasons:    []string{"agent network budget rule"},
+			expectedNotDeleted: []string{"grp-for-agent-network-budget-rule"},
+		},
 		{
 			name:               "reverse proxy services",
 			groupIDs:           []string{"grp-for-rp-private", "grp-for-rp-bearer"},
@@ -501,6 +522,14 @@ func initTestGroupAccount(am *DefaultAccountManager) (*DefaultAccountManager, *t
 		Peers:     make([]string, 0),
 	}
 
+	groupForAgentNetworkBudgetRule := &types.Group{
+		ID:        "grp-for-agent-network-budget-rule",
+		AccountID: "account-id",
+		Name:      "Group for agent network budget rules",
+		Issued:    types.GroupIssuedAPI,
+		Peers:     make([]string, 0),
+	}
+
 	groupForRPPrivate := &types.Group{
 		ID:        "grp-for-rp-private",
 		AccountID: "account-id",
@@ -573,6 +602,7 @@ func initTestGroupAccount(am *DefaultAccountManager) (*DefaultAccountManager, *t
 	_ = am.CreateGroup(context.Background(), accountID, groupAdminUserID, groupForUsers)
 	_ = am.CreateGroup(context.Background(), accountID, groupAdminUserID, groupForIntegration)
 	_ = am.CreateGroup(context.Background(), accountID, groupAdminUserID, groupForAgentNetworkPolicy)
+	_ = am.CreateGroup(context.Background(), accountID, groupAdminUserID, groupForAgentNetworkBudgetRule)
 	_ = am.CreateGroup(context.Background(), accountID, groupAdminUserID, groupForRPPrivate)
 	_ = am.CreateGroup(context.Background(), accountID, groupAdminUserID, groupForRPBearer)
 
@@ -587,6 +617,20 @@ func initTestGroupAccount(am *DefaultAccountManager) (*DefaultAccountManager, *t
 		return nil, nil, err
 	}
 
+	budgetRuleDecoy := agentNetworkTypes.NewAccountBudgetRule(accountID)
+	budgetRuleDecoy.Name = "Unrelated agent network budget rule"
+	budgetRuleDecoy.TargetGroups = []string{"unrelated-group"}
+	if err := am.Store.SaveAgentNetworkBudgetRule(context.Background(), budgetRuleDecoy); err != nil {
+		return nil, nil, err
+	}
+
+	budgetRule := agentNetworkTypes.NewAccountBudgetRule(accountID)
+	budgetRule.Name = "Example agent network budget rule"
+	budgetRule.TargetGroups = []string{groupForAgentNetworkBudgetRule.ID}
+	if err := am.Store.SaveAgentNetworkBudgetRule(context.Background(), budgetRule); err != nil {
+		return nil, nil, err
+	}
+
 	// The decoy services are created first so the linkage check has to scan
 	// past services that do not reference the groups under test.
 	rpServices := []*rpservice.Service{