Streaming flow runtime: continuously evaluates registered flow definitions over the change stream coming out of the transaction layer, applies the operator graph the planner produced, and writes the resulting deltas back into the catalog so downstream queries observe a derived view that updates in step with its inputs.
The runtime hosts both built-in operators and FFI-loaded ones from extensions, threading them through a shared deferred-work queue so backpressure from a slow consumer does not block fast ones. Connectors at the edges of the graph translate between the engine's internal column shape and external sources/sinks.
Invariant: a flow's output for a given input set is fully determined by its definition - replaying the same input deltas through the same flow definition produces the same output deltas. Operators that introduce hidden state (a clock, a random number, an external read that may differ between runs) break this guarantee and break replay.