Per mara's direction — validate ids as they enter the graph so internal
iteration can trust every id the graph holds; the generational route for
removal comes later. Adds GraphError; insert() now rejects a dangling
Dep::Node / parent id (it is fallible); validate() checks all internal id
references resolve and that next_id is past the largest existing id;
deserialization runs validate() via #[serde(try_from = "GraphData<N>")], so
a loaded graph can never carry a dangling reference. 5 new tests; serde_json
added as a dev-dependency for the round-trip cases.
First step of extracting the job-DAG queue into a domain-agnostic
`hive-jobq` library, per the operator's v2 design: one persistent
graph, named-counter resources, recursive node groups, opaque stable
node ids, guard-object locks, a slot-filling scheduler.
This commit lands only the data model, so the shape can be reviewed
before the machinery is built on it:
- NodeId: opaque, stable, monotonic; group membership is a parent
edge, not encoded in the id (the 1/1/2 hierarchy is a derived UI
label).
- ResourceName, Dep (Node | Resource{name,count}), State.
- Node<N>: caller-defined payload N so the library stays
container-agnostic.
- Graph<N>: insert (mints stable ids), node lookup, children,
recursive group-terminal check. Retains completed groups (no
pruning in v1).
The resource-acquisition machinery (atomic all-or-nothing acquire),
the recursive-lock guards, and the scheduler loop are follow-ups.
Tests cover id minting, group terminality, and state terminality;
clippy + rustdoc clean.
