emit stamps the ADR 0047 headers — x-event-id, x-source, x-node, x-time,
content-type, and optional x-causation-id / x-schema — and publishes the
body as only the domain payload. on() reconstructs the Event from those
headers. Event gains id (the x-event-id a consumer dedups on) plus the
optional causation/schema. EventHeaders joins the contracts spine.
Supersedes the first cut that carried source/node/time in the body.
Claude-Session: https://claude.ai/code/session_01LrgweAeERJYBg88c5cKDzF
jschoubben
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