r.defineEvent(...)
Overview
Section titled “Overview”r.defineEvent(name, schema, options?) — registers an event payload
shape and returns the qualified EventDef, so callers pass .name to
ctx.events.append instead of hand-building <feature>:event:<short>.
options.version declares the CURRENT schema generation (default 1).
options.migrations is a step-wise upcast chain — keyed by fromVersion
(toVersion is always fromVersion + 1, enforced at registration, so it is
not stored separately); the framework refuses to boot if the chain from
1 to version has gaps. Formerly a separate r.eventMigration() call
per step, folded in here — an event and its schema
evolution are one lifecycle, not two registrar concepts.
From packages/feature-ast/src/patterns.ts -> DefineEventPattern