<hive-jobq-graph> only ever drew the parent/child containment tree --
a dependency between two sibling nodes (same parent, e.g.
prebuild.after_ok(meta_sync)) was invisible on screen. Confirmed with
the operator that a Node-kind dep never crosses a group boundary
(always a sibling under the same parent), so this is a purely local
problem per sibling list, not a whole-graph layout question.
Each sibling list is reordered dependency-first (stable topo sort,
falls back to original order on ties or an unexpected cycle) and gets
a small connecting rail in its left gutter marking dep edges, with a
tooltip naming what a waiting node is blocked on. Groups with no deps
render exactly as before -- no extra markup, no cost.
Verified the ordering + rail-classification logic standalone against
constructed fixtures (9 + 12 checks) before trusting it in the real
component.