I2.6 — Parity & ordering validation vs MassTransit baseline

[nickna]

Phase 2 · Size M · Risk: HIGH (GATE)

Scope

• Side-by-side validation: spend per-key ordering under load, webhook deferral timing, throughput, no message loss.
• Compare against captured MassTransit behavior.

Acceptance criteria

• Documented parity report; sign-off to cut over.

Dependencies

I2.3, I2.4, I2.5.

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Part of #909 — Messaging Migration epic.