refactor(#2949): the build-log row carries its node id

`QueueInner` was `{ sched, node_rt }`, where `node_rt` held exactly one
datum per node: the `build_logs` row id. It existed because a `hive_jobq`
node payload is immutable after insert while the log row is created when
the build starts — so the link could not ride the node.

Invert it: the log row names its node (`build_logs.node_id`, one migration
in the existing `schema_versions` framework). Same single-home property,
in the direction the type system allows.

`QueueInner` is now just the scheduler. That is the point: the queue holds
no per-node side map, so nothing has to be locked alongside the graph.

Deleted as a consequence, each surfaced by dead-code analysis after the
edit above rather than predicted:

- `NodeRuntime`, `node_rt`, `set_build_log_id`, and `build_log_id_of`
  (which linear-scanned the map to match a wire `u64` against opaque
  `NodeId`s). The lookup is an indexed query now.
- `struct Ctx`, entirely. It carried `coord` + `dag_id` + `node_id` into
  the executors so the build-log callback could reach the queue; without
  the callback, `coord`/`dag_id` were never read and `node_id` was already
  on the `Claim` both executors receive.
- `QueueInner::node_running`, which existed only for `set_build_log_id`'s
  "only while running" guard.
- The `Fn(i64)` callbacks on `prebuild_toplevel` / `swap_update` /
  `priv_run_inner`, replaced by a `node_id: Option<u64>` passed down. The
  id travels one way now instead of being registered back.

`meta.rs`'s `nix_logged` passes `None` deliberately: its callers reach it
from outside the queue as well as inside, and nothing reads the link for
them yet.

`id_for_node` takes `MAX(id)` rather than assuming uniqueness — a retried
node opens a second row and the panel wants the current attempt. The test
moved to where the behaviour lives and covers that, plus survival across
completion and non-collision with node-less rows.

hive-c0re/src/job_queue/tests.rs

@@ -1544,27 +1544,12 @@ fn deploy_dag_skips_apply_but_still_runs_tail_when_verify_fails() {
     assert_eq!(state_of(&q, id), State::Failed);
 }
 
-// ---- build logs, history ----
-
-#[test]
-fn set_build_log_id_links_running_node() {
-    let q = JobQueue::new(1);
-    let id = submit(&q, rebuild("agent-a", "r"));
-    let c = claim_one(&q);
-    assert!(q.set_build_log_id(id, c.node_id, 42));
-    q.complete_node(c.node_id, Ok(()));
-    assert!(
-        !q.set_build_log_id(id, c.node_id, 99),
-        "node no longer running → refused"
-    );
-    // The log id is fetched by node id (the `GET /api/build-log/<id>` lookup),
-    // not carried on the wire — it survives completion in the node runtime.
-    assert_eq!(
-        q.build_log_id_of(c.node_id.get()),
-        Some(42),
-        "log id survives completion"
-    );
-}
+// ---- history ----
+//
+// The node → build-log link is no longer queue state: the log row carries
+// `node_id` and the lookup lives in `stores::build_logs` (see
+// `node_link_survives_completion_and_newest_wins` there). Nothing in the queue
+// needs testing for it any more, which is the point of that move.
 
 /// History retention is a **flat** newest-first cap over all terminal DAGs
 /// (`MAX_HISTORY_DAGS`), not a per-template bucket behind a grace window.