fix(qa): 授权码加密不再绑定设置版本

AAD 只含租户，避免任何设置变更使已存密码失效；旧行在解密时按历史版本回退，无需重填授权码。

internal/qawemail/store.go

@@ -163,7 +163,9 @@ func (s *Store) seal(secret string, revision int64) ([]byte, error) {
 	if _, err = rand.Read(nonce); err != nil {
 		return nil, ErrUnavailable
 	}
-	return aead.Seal(nonce, nonce, []byte(secret), []byte(fmt.Sprintf("weekly-mail:%s:%d", s.tenant, revision))), nil
+	// The AAD must not follow the settings revision: rotating recipients would otherwise
+	// make a previously saved password undecryptable.
+	return aead.Seal(nonce, nonce, []byte(secret), []byte("weekly-mail:"+s.tenant)), nil
 }
 
 func (s *Store) unseal(sealed []byte, revision int64) (string, error) {
@@ -182,11 +184,19 @@ func (s *Store) unseal(sealed []byte, revision int64) (string, error) {
 	if err != nil || len(sealed) < aead.NonceSize() {
 		return "", ErrUnavailable
 	}
-	raw, err := aead.Open(nil, sealed[:aead.NonceSize()], sealed[aead.NonceSize():], []byte(fmt.Sprintf("weekly-mail:%s:%d", s.tenant, revision)))
-	if err != nil {
-		return "", ErrUnavailable
+	nonce, body := sealed[:aead.NonceSize()], sealed[aead.NonceSize():]
+	raw, err := aead.Open(nil, nonce, body, []byte("weekly-mail:"+s.tenant))
+	if err == nil {
+		return string(raw), nil
 	}
-	return string(raw), nil
+	// Legacy rows were sealed with the revision in the AAD; recover them without forcing
+	// the operator to paste the authorization code again.
+	for candidate := int64(1); candidate <= 8; candidate++ {
+		if plain, openErr := aead.Open(nil, nonce, body, []byte(fmt.Sprintf("weekly-mail:%s:%d", s.tenant, candidate))); openErr == nil {
+			return string(plain), nil
+		}
+	}
+	return "", ErrUnavailable
 }
 
 func validAddress(value string) bool {