Struct ExpandRequest 

pub struct ExpandRequest {
    pub frontier: Vec<NodeId>,
    pub direction: Direction,
    pub edge_types: Option<TypeIdSet>,
    pub labels: Option<LabelFilter>,
    pub budget: HopBudget,
    pub with_degrees: bool,
}

Directed one-hop expansion request. Direction is explicit because the undirected shorthand plans as an all-vertex probe; expansion is a one-hop primitive because multi-hop chain patterns enumerate paths and explode on hubs.

Fields

frontier: Vec<NodeId>

direction: Direction

edge_types: Option<TypeIdSet>

Per-hop restriction, already resolved to registered types.

labels: Option<LabelFilter>

Per-hop restriction (labels are deferred; engines may answer Unsupported).

budget: HopBudget

with_degrees: bool

Ask for ExpandResponse::degrees to be filled.

Off by default because it costs a second scoped read: the edges incident to the reached set, not only to the frontier. A traversal does not need it — its caller post-processes the whole region — and a neighborhood projection cannot do without it, because that is what decides which neighbours of a hub survive the node budget.