feat: allow network admin to control ephemerality setting

Resolves #92

go/internal/network/service.go

@@ -13,6 +13,7 @@ import (
 var ErrNotFound = errors.New("network not found")
 var ErrInvalidName = errors.New("name cannot be empty")
 var ErrCapacityExceeded = errors.New("active stream capacity exceeded")
+var ErrInvalidRetentionHours = errors.New("message retention hours must be between 24 and 336")
 
 type Service interface {
 	// Create creates a network and adds adminHumanId as the first member. Returns ErrInvalidName if name is empty.
@@ -25,6 +26,8 @@ type Service interface {
 	RemoveMember(ctx context.Context, networkID, humanId string) error
 	ListForHuman(ctx context.Context, humanId string) ([]*Network, error)
 	IsMember(ctx context.Context, networkID, humanId string) (bool, error)
+	// SetMessageRetentionHours sets how long messages remain visible (24–336 hours).
+	SetMessageRetentionHours(ctx context.Context, id string, hours int) error
 
 	// Invitations (email-based, for users who haven't registered yet)
 	InviteByEmail(ctx context.Context, networkID string, emails []string) error
@@ -115,6 +118,17 @@ func (s *serviceImpl) IsMember(ctx context.Context, networkID, humanId string) (
 	return s.repo.isMember(ctx, networkID, humanId)
 }
 
+func (s *serviceImpl) SetMessageRetentionHours(ctx context.Context, id string, hours int) error {
+	if hours < 24 || hours > 336 {
+		return ErrInvalidRetentionHours
+	}
+	err := s.repo.updateMessageRetentionHours(ctx, id, hours)
+	if errors.Is(err, errNotFound) {
+		return ErrNotFound
+	}
+	return err
+}
+
 // Invitation methods
 
 func (s *serviceImpl) InviteByEmail(ctx context.Context, networkID string, emails []string) error {