mara reported the rail still didn't make dependencies visible
(screenshot on the PR). Root cause: the rail spans by sibling-array
position, but a sibling with its own nested subtree renders many
pixel-rows for one array slot -- in a real queue (agent_window with
7-ish children between two top-level siblings), the "line" breaks
into disconnected ticks around every real subtree, never reading as
a connection at all. My verification fixtures never tested a nested
subtree sitting between two related siblings, so this never showed up
before.
Replaced with a "waits on: <label>" text line under the dependent
node, resolved once in buildTree via a global id lookup (not scoped to
siblings, so a label still resolves even if a dep ever does cross a
group boundary despite the product decision that it shouldn't). Text
has no positional-gap failure mode: it's legible regardless of how
tall the node above or below it renders. No reordering, no rail, no
interleaving-of-independent-pairs class of bug possible anymore --
this is close to the original design proposed on the issue before the
heavier visual version was tried.
Re-verified against 6 fixture checks including the exact shape from
the screenshot (a dependency target with its own nested subtree
rendered between it and the dependent node).
a858739b28