Flows & VejasScript

A flow is one file under flows/: a pure, per-event program. One trigger (source subject, api route, or MCP tool), transformations, emits and/or a respond. No I/O, no clock, no network — the language cannot express them. That purity is load-bearing:

• the business surface (UPPERCASE literals) can be extracted, shown and edited safely — a change is a literal swap plus a unit restart;
• any persisted event can be replayed through any version of the flow with zero side effects — which is what makes time-travel and canary structural rather than bolted on;
• a fixture plus vejas_run_flow is a complete test.

The language fits in 20 lines — see the VejasScript reference. Highlights: null-safe access (requester?.email), array projection/filtering (orders[total > 100]), f-strings, transcoding via literal dicts, invoke to compose services (services/<name>.vjs, cross-package with EXPORTS), secret("path/key") for credentials — never a literal.

Lifecycle

The supervisor watches VEJAS_ROOT: a new or changed file becomes a running unit; a broken one fails loudly without taking the rest down. Each flow gets a durable consumer on its source subject, so stopped is not losing: events accumulate on the stream and drain on restart. Tests live next to the code (tests/vjs/ golden cases, per-flow fixtures) and run in CI with vejas-runtime vjs-test.