I1.9 — Phase 1 verification gate: regression on MassTransit-backed abstraction

[nickna]

Phase 1 · Size S · Risk: low (GATE)

Scope

• Full dotnet test.
• Staging smoke: admin edit -> gateway invalidation; image/video gen; webhook; spend.
• Confirm zero behavior change; tag a release.

Acceptance criteria

• Regression clean in staging; Phase 1 merged to dev. MassTransit still underneath — safe checkpoint.

Dependencies

I1.4–I1.8.

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Part of #909 — Messaging Migration epic.