Boots a real Postgres (no Docker), applies the real migration and seed,
starts the real go-smtp server wired as main.go does, and drives a live
SMTP session. Asserts: 550 for unknown RCPT, durable EML + row with
uid_next allocation, sha256 disk/db match, outbox event, blob dedup with
ref_count. Documents the counters gap (PLAN 6.1) as an explicit skip.
Phase: F1 validation
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>