findings of the reviews of audit stage 2

Technical review (Opus) and security review (Fable) of a59e3d4..cb5a4a2;
reports in the session's scratchpad. Nothing critical, high or medium; no
outright bug. Fixed:

- F2, F3 (0008 backfill, before it runs on the live database): rows are
  filled by the rule new rows follow - the application's domain, then the
  name's - and only by a domain and application that existed when the row
  was written (created_at); the inbound log likewise. Test: the migration's
  UPDATEs re-run on prepared rows (before the domain, after, null sender,
  application gone, a stranger's name). Dry run on a copy of the live
  database: 68/68 and 10/10 rows filled, none disagreeing with its login's
  domain, integrity ok.
- V2, F4: an application's statistics and level-2 count are its login's
  rows of its domain (appByLogin), and StatsWindow starts no earlier than
  the entity's creation; the message page's "may send as" only for a login
  still of the row's domain. Test: a login taken again in another domain
  starts at zero.
- F7: MAIL FROM:<> is held to the domain limit of its login
  (ApplicationByLogin fills DomainName).
- V3: an imported DKIM selector is held to DNS labels (validate.Selector).
- F5, F6: an imported auto limit's numbers are dropped and recalculated
  right after the import; its mode is stored trimmed.
- V6: the store refuses a role that is neither global nor domain.
- F9: SaveUser keeps the stored hash when no new password is given (the
  form no longer writes back the hash it read). F10: a reach naming a
  domain deleted meanwhile is ErrNoSuchDomain, answered on the form.
- V4, F12: from-lines-other.txt - lines naming another sender ({other}) in
  a quoted string, a quoted pair, capitals, a comment, an encoded word, a
  quoted local part; the unit test wants each refused, the e2e
  (lines_naming_another_sender_never_signed_for_it) wants each refused and
  none signed for it. The passed list gained a.{DOMAIN}, a comment after
  the angle address, a quoted local part, and "b@ {other}" - passed by
  design (security.md), and the e2e shows it signed for the own domain.
- F13: e2e login_in_other_capitals_does_not_authenticate - AUTH with the
  login upper-cased gets 535.

Not changed, written down: V1/F1 - L8 is half closed (refused or passed
still tells an application which domains are hosted here); security.md's
accepted risks and the CHANGELOG say so, and the owner is asked whether to
refuse every foreign address in a display name (changes the 2.4.0 rule).
F11 - deleting a domain rewrites its rows' domain_id (seconds at 1e5 rows),
accepted at this size. F8 (test cannot tell write-first from read-first;
the reviewer verified it with two stores, 30/30), V5, V7, P2: noted.

Evidence on the test server for this tree: go vet clean, go test ./... 23
packages ok, make e2e exit 0 with the three new cases.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

internal/store/sendlog_test.go

@@ -401,3 +401,36 @@ func TestADomainAddedAgainStartsWithAnEmptyLog(t *testing.T) {
 		t.Fatalf("statistics = %+v, %v; want one message", stats, err)
 	}
 }
+
+// A deleted application's login taken again in another domain starts with
+// none of the old one's numbers (review of audit stage 2).
+func TestALoginTakenAgainStartsWithNoNumbers(t *testing.T) {
+	st := openTestStore(t)
+	a := addTestDomain(t, st, "a.example")
+	b := addTestDomain(t, st, "b.example")
+	old, err := st.AddApplication(a.ID, "news", AddressModeWildcard, nil)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if err := st.InsertQueued(SendLogEntry{QueueID: "OLD", Domain: "a.example", AppLogin: "news", To: "x@example.net"}); err != nil {
+		t.Fatal(err)
+	}
+	if _, err := st.DeleteApplication(old.ID); err != nil {
+		t.Fatal(err)
+	}
+	if _, err := st.AddApplication(b.ID, "news", AddressModeWildcard, nil); err != nil {
+		t.Fatal(err)
+	}
+	if n, err := st.CountMessages(RateLimitScopeApp, "news", time.Now().Add(-time.Hour)); err != nil || n != 0 {
+		t.Fatalf("level-2 count of the new news = %d, %v; want 0", n, err)
+	}
+	if stats, err := st.AppSendStats("news", 90, time.Now().Add(-time.Hour)); err != nil || stats.Total != 0 {
+		t.Fatalf("statistics of the new news = %+v, %v; want none", stats, err)
+	}
+	if err := st.InsertQueued(SendLogEntry{QueueID: "NEW", Domain: "b.example", AppLogin: "news", To: "x@example.net"}); err != nil {
+		t.Fatal(err)
+	}
+	if n, _ := st.CountMessages(RateLimitScopeApp, "news", time.Now().Add(-time.Hour)); n != 1 {
+		t.Fatalf("level-2 count of the new news = %d, want its own one", n)
+	}
+}