Fixes a real bug argus caught: the flat batch-round topo sort could
interleave two fully independent dep pairs in the same sibling list
(e.g. W, X after_ok(W), Y, Z after_ok(Y) reordered to W, Y, X, Z), and
the single-column rail then drew one continuous line across rows that
have no relationship at all.
Reorder is now scoped per connected component of the local dependency
graph -- each component renders as a contiguous block (first-seen
order, so an already-correct list doesn't reorder needlessly), so two
unrelated pairs can never weave together. Within one component,
overlapping ranges are still correct: they mean the nodes really are
related (a diamond, for instance).
Also: a pass-through row's tooltip now names what's passing through it
(not just the edge it's itself an endpoint of) -- addresses the same
disambiguation gap argus flagged as a secondary note.
Re-verified against a wider fixture set including the exact
interleaving case from the review (17 checks: prior 6 unaffected +
argus's regression case, a shuffled-order variant, three simultaneous
independent pairs, and a genuine diamond that's expected to overlap).
6f87821110