mara's review comment: the frontend shouldn't apply its own grouping
logic on top of the DAG — it should render the structure the backend
already provides. The actual structure is the nodes' deps graph, not
the incidental n.agent field.
Replace the group-by-agent heuristic with nodeComponents(): splits
entry.nodes into weakly-connected components via the deps edges
(undirected reachability), then topo-sorts each component (Kahn's
algorithm) so a chain renders in true dependency order. A DAG made of
independent per-agent subgraphs (no cross-agent deps) still comes back
as separate components — same visual result for today's templates —
but the split is now driven by what the backend actually encodes, and
naturally extends to any future non-agent-aligned branching. Agent
name is still shown as a per-component label, but purely as adjunct
info sourced from that component's own nodes, not the grouping key.
44286996ed