Replace the in-tree scheduler with the domain-agnostic hive-jobq crate
(merged in #2615): parent-axis grouping + borrow/subtree-reservation
resource model + roll-up completion (State::Finishing).
Host adaptation:
- NodeSpec gains an explicit `parent` axis; templates declare grouping +
sibling ordering directly (deps order execution, parent groups a subtree
whose resource the descendants borrow).
- Rebuild is a nested two-root subtree: Prebuild (root, owns the build slot
for the whole subtree, lease-exempt) -> StopForUpdate (child, owns the
agent lease) -> Swap/PostSwap (children, borrow both); Reconcile is a
separate top-level root (AfterAny Prebuild) so it survives the cancel-
cascade of any failed step (recovery-start invariant) and converges to
the persisted `wanted` on a fresh lease. This is the multi-root
correction to the single-root-chain sketch: node0=root broke lease-
exemption (hoisting the lease onto Prebuild) and recovery-reconcile
(root failure cancels all children).
- Spawn / perm-change / power-ops (stop/start/restart) group-rooted the
same way; per-agent power-op subgraphs stay independent roots so a
multi-agent DAG runs them concurrently, each on its own lease.
- insert_group honours the explicit parent axis (no lease hoisting); the
DAG terminal node deps AfterAny on every group root and runs once the
whole op rolls up. Drop the old Graph::add_dep terminal wiring.
36/36 job_queue tests, full hive-c0re suite green, clippy --all-targets.
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