#3: close 3 known F1 gaps - folder/mailbox counters, quota-at-RCPT, alias fan-out

Per feature/3-f0-f1-validation's own gap analysis (commit 097fa37):

- InboundMessageRepository.Persist now updates folders.unread_count,
  folders.total_count, and mailboxes.used_bytes in the same transaction
  as the message insert (PLAN.md section 6.1 "++counters" was a no-op
  before this).
- MailboxRecord carries QuotaBytes/UsedBytes; ResolveRecipient rejects
  RCPT with 452 4.2.2 when a target mailbox has already reached its
  quota (used_bytes >= quota_bytes), before DATA - never silently
  accepting mail into a full mailbox.
- MailboxRepository.ResolveDeliveryTargets tries a direct mailbox match
  first, then falls back to the aliases table (exact source_address
  match takes precedence over a domain catch-all). One RCPT TO can now
  fan out to multiple mailboxes; alias destinations that don't resolve
  to an internal active mailbox are silently skipped, since outbound/
  external forwarding doesn't exist yet. postmaster@/abuse@/dmarc@-style
  aliases now actually deliver.

The E2E test's counters_updated subtest flips from a documented KNOWN
GAP (t.Skipf) to a hard assertion now that it passes, and gains two new
subtests (quota_rejected_when_mailbox_full, alias_resolves_to_destination_mailbox)
covering the other two fixes end-to-end. New unit and Postgres
integration test coverage added for all three fixes at every layer.

Verified: full suite green on Windows (unit + E2E via embedded
Postgres, no Docker needed) and via WSL Docker against the real
docker-compose Postgres (all infrastructure/postgres and diskstorage
integration tests, not just E2E). lang-lint clean.

services/protocols/internal/application/usecase/process_inbound_email.go

@@ -14,6 +14,13 @@ import (
 // mailbox matches - the presentation layer maps this to SMTP 550 5.1.1.
 var ErrRecipientNotFound = errors.New("process inbound email: recipient not found or inactive")
 
+// ErrMailboxQuotaExceeded is returned by ResolveRecipient when a resolved
+// target mailbox has already reached its storage quota - the presentation
+// layer maps this to SMTP 452 4.2.2. If a single RCPT resolves to multiple
+// mailboxes (alias fan-out) and any one of them is full, the whole RCPT is
+// rejected rather than partially delivering.
+var ErrMailboxQuotaExceeded = errors.New("process inbound email: mailbox has reached its storage quota")
+
 // ProcessInboundEmailInput carries one SMTP DATA transaction's worth of
 // state: the accumulated recipients from one or more successful Rcpt calls,
 // and the message body stream.
@@ -38,16 +45,23 @@ func NewProcessInboundEmailUseCase(mailboxes port.MailboxRepository, blobs port.
 	return &ProcessInboundEmailUseCase{mailboxes: mailboxes, blobs: blobs, messages: messages}
 }
 
-// ResolveRecipient is called from the SMTP session's RCPT TO handler.
-func (uc *ProcessInboundEmailUseCase) ResolveRecipient(ctx context.Context, address string) (*port.MailboxRecord, error) {
-	rec, err := uc.mailboxes.FindActiveByAddress(ctx, address)
+// ResolveRecipient is called from the SMTP session's RCPT TO handler. It
+// returns every mailbox address should be delivered to (more than one for
+// an alias that fans out), or ErrRecipientNotFound / ErrMailboxQuotaExceeded.
+func (uc *ProcessInboundEmailUseCase) ResolveRecipient(ctx context.Context, address string) ([]port.MailboxRecord, error) {
+	targets, err := uc.mailboxes.ResolveDeliveryTargets(ctx, address)
 	if err != nil {
 		return nil, err
 	}
-	if rec == nil {
+	if len(targets) == 0 {
 		return nil, ErrRecipientNotFound
 	}
-	return rec, nil
+	for _, t := range targets {
+		if t.UsedBytes >= t.QuotaBytes {
+			return nil, ErrMailboxQuotaExceeded
+		}
+	}
+	return targets, nil
 }
 
 // Handle is called once from the SMTP session's DATA handler, after one or