`nix_logged` wrote its `build_logs` row with `node_id = None`, so a deploy's
eval/relock log was reachable from the agent+kind+time listing but not from
the queue node that ran it.
The comment justifying the `None` said both callers are "reached from outside
the queue as well as from inside it". That is no longer true: `verify_commit`
and `prepare_deploy` have exactly one caller each, and both sit under the
`MergeVerify` / `DeployApply` arms of `exec.rs`'s node dispatch, where the
`NodeId` is already in scope.
Threads `Option<u64>` from the dispatch down, mirroring `prebuild_toplevel`'s
existing `Some(id.get())` at exec.rs:241. Kept as `Option` rather than a bare
`u64` because `meta::prepare_deploy` / `meta::verify_commit` are public API and
a future non-queue caller has no node to name; the comment now says that
instead of the stale claim.
No behaviour change beyond the log row gaining its node link.
6ce71556e2