jobq: split RebuildOpts into two rebuild entry points

RebuildOpts held one real parameter (relock) and one single-call-site
flag (graceful). The struct justified itself as swap-protection for two
positional bools; with graceful out of the signature there is nothing
left to swap.

graceful stays an internal switch rather than moving to the caller: it
re-parents the stop root (StopForUpdate goes from part_of(prebuild) to
part_of(signal)) rather than prepending nodes, so a caller could only
declare it by being handed the subtree's internals — and that nesting
keeps the agent lease continuous across the whole stop.

run_meta_lock no longer returns options: both fields were a pure
function of the sweep flag its caller had just passed in.

315 tests pass unchanged.

hive-c0re/src/job_queue/submit.rs

@@ -26,7 +26,7 @@ use std::sync::Arc;
 
 use super::model::NodeKind;
 use super::resource::Resource;
-use super::templates::{RebuildOpts, rebuild_nodes};
+use super::templates::rebuild_nodes;
 use super::{Job, Source, templates};
 use crate::coordinator::Coordinator;
 use crate::lifecycle;
@@ -118,15 +118,7 @@ fn start_chain(b: &Job, agent: &str, running: bool, stale: bool) {
         // Rebuild subtree chained behind the `SetWanted` head. `MetaSync`,
         // `Prebuild` + `Reconcile` are their own group roots (top-level, per
         // `rebuild_nodes`).
-        rebuild_nodes(
-            b,
-            agent,
-            RebuildOpts {
-                relock: true,
-                graceful: false,
-            },
-            Some(wanted),
-        );
+        rebuild_nodes(b, agent, true, Some(wanted));
     } else {
         let _ = b
             .node(NodeKind::Reconcile {