pa-03 — Verification

One command

cd pa-03-event-driven-architecture && bash scripts/verify.sh

Test	Invariant
`TestFanOut`	one publish reaches all subscribers
`TestTopicIsolation`	a subscriber never sees other topics' events
`TestRetryThenSucceed`	a transient failure recovers via retries; not dead-lettered
`TestPoisonGoesToDLQ`	a permanent failure is dead-lettered after maxRetries+1 attempts; never delivered
`TestIdempotentDedup`	duplicate ids are processed once (effectively-once)
`TestDistinctEventsBothRun`	distinct ids each run

All under -race.

Synchronous, in-memory bus. Production is a durable partitioned log (pa-04) with async consumer groups; backpressure/ordering are exercises.
No cross-event ordering. Ordering is per-partition (pa-04), not global.
No tracing across the async hop — the hard observability problem (gw-11), out of scope here.