fix(multiplayer): harden reconnect lifecycle fencing

server/domain/reconnect.go

@@ -91,6 +91,9 @@ func (r *RankedConnections) validate(auth JoinAuthorisation, now time.Time) erro
 // slot with the next server-owned generation. A newer generation fences every
 // older connection, even if the backend is temporarily unavailable.
 func (r *RankedConnections) Admit(auth JoinAuthorisation, now time.Time) (uint64, error) {
+	if now.IsZero() {
+		return 0, ErrJoinAuthorisation
+	}
 	if err := r.validate(auth, now); err != nil {
 		return 0, err
 	}
@@ -107,7 +110,13 @@ func (r *RankedConnections) Admit(auth JoinAuthorisation, now time.Time) (uint64
 	if player.Abandoned {
 		return 0, ErrReconnectExpired
 	}
+	if !player.ConnectedAt.IsZero() && player.LostAt.IsZero() {
+		return 0, ErrConnectionFenced
+	}
 	if !player.LostAt.IsZero() {
+		if now.Before(player.LostAt) {
+			return 0, ErrJoinAuthorisation
+		}
 		if now.Sub(player.LostAt) > RankedReconnectGrace {
 			return 0, ErrReconnectExpired
 		}
@@ -120,6 +129,9 @@ func (r *RankedConnections) Admit(auth JoinAuthorisation, now time.Time) (uint64
 }
 
 func (r *RankedConnections) Disconnect(playerID string, generation uint64, now time.Time) error {
+	if now.IsZero() {
+		return ErrJoinAuthorisation
+	}
 	player, ok := r.players[playerID]
 	if !ok {
 		return ErrJoinAuthorisation
@@ -130,6 +142,9 @@ func (r *RankedConnections) Disconnect(playerID string, generation uint64, now t
 	if player.Abandoned {
 		return ErrReconnectExpired
 	}
+	if player.ConnectedAt.IsZero() || !player.LostAt.IsZero() || now.Before(player.ConnectedAt) {
+		return ErrConnectionFenced
+	}
 	player.LostAt = now
 	r.players[playerID] = player
 	return nil