Highwater: Stateful Applications on Event Streams

Field notes

Highwater models event-driven programs as long-lived state machines rather than disposable handlers. Its SupportAgent example stores a session turn count, invokes a model, waits for an approval event for up to 24 hours, and resumes from committed state. The page also illustrates batching by model and request shape, with dispatch triggered by either a full batch or a latency limit, alongside event-time watermarks for late records.