Introduces a discriminated Actor union (user | ai | system) threaded through
the event pipeline so downstream consumers can distinguish human writes from
AI-initiated ones and derived subsystem writes.
- `EventMeta.actor: Actor` is required (no legacy fallback — pre-launch)
- `emitDomainEvent` takes an options bag `{ actor?, causedBy? }`; falls back
to the ambient actor set by `runAs` / `runAsAsync`
- `runAs` / `runAsAsync` pin the actor at defined boundaries (tool executor,
mission runner, projection dispatcher) — primitives capture synchronously
so ambient context is never SoT past the write moment
Foundation for the AI Workbench. Follow-up: mana-sync server must accept
and persist `actor` in pending-change payloads.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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