Extends the existing happy-path test (one case) with 14 more covering
every branch of the receiver-side handler: missing payload, attribution
mismatch, tombstoned sender (silent accept), recipient_not_found
(including soft-deleted recipient), already-friends idempotency in both
column orderings, same-direction pending re-delivery idempotency,
declined-then-resent (status filter), reused replicated stub, profile
hydration with URL resolution, explicit and fallback createdAt, and
mixed-batch accept/reject isolation through processRelayEvents.
Jannis Braun
8cad964809