Address review feedback on PR #1738:
- ReactLoopAgent builds its AgentEventDispatch once in the constructor and
routes every emit/serial/waterfall through it, so hot-path dispatches no
longer allocate a carrier and dispatcher per call; the public carrier
field is gone (fused dispatcher is private).
- agentEvents accepts an optional prebuilt carrier.
- The fused payload builder spreads the payload before the injected agent
so a structurally acceptable payload carrying an agent field can never
override the subject.
- Regenerate doc graphs; re-record core + architecture + affected Agent
Note translation pairs; add payload-object event contract Agent Note.
_Kerman
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