facade (API only extended): oakengine_sequence_as_node /
_sequence_node_count / _sequence_node_at / _sequence_remove_node;
remove validates ownership by project UUID (arena slot/generation
collide across projects). it_node covers enumeration/edits and the
NULL/illegal matrix.
app: NodeGraphDataSource enumerates the current sequence's graph —
footage / effect / clip / output cards at their context positions
(deterministic role-grid fallback), real edges plus synthesized
clip->sequence tex_in edges; connect/disconnect/remove/drag-release
all go through undoable facade commands, drag previews stay local.