The ESCAPE HATCH: declare an arbitrary recompute MODULE (a ReactiveDag.Op)
for a node whose computation the reduce/join combinators can't express —
an LLM call, a PDF/Tigris fetch, a bespoke multi-input recompute. compute MyApp.EventsExtract sits in the block alongside the combinators, mirroring
Ash's calculate :x, :type, MyModule (the arbitrary case is an entity too,
not a schema key beside the declarative ones).