send AI verification code through the conversation's inbox

The OTP email went out over the notification email channel, which uses a separate SMTP config and a different sender. Now email conversations send the code through their own inbox, reusing the conversation subject so it threads into the same email thread instead of a new one. Livechat still falls back to the notification channel since it can't send email.

internal/aiagent/tools.go

@@ -249,14 +249,27 @@ func (t *sendEmailVerificationTool) Execute(ctx context.Context, args string) (s
 		return "", err
 	}
 	body := t.m.i18n.Ts("ai.agent.verificationEmailBody", "code", code)
-	if err := t.m.notifier.Send(notifier.Message{
-		RecipientEmails: []string{email},
-		Subject:         t.m.i18n.T("ai.agent.verificationEmailSubject"),
-		Content:         body,
-		Provider:        notifier.ProviderEmail,
-	}); err != nil {
-		t.m.lo.Error("error sending verification code email", "conversation_uuid", t.conv.UUID, "error", err)
-		return "", err
+	// Livechat inboxes can't send email, so those fall back to the notification email channel.
+	var sendErr error
+	if t.conv.InboxChannel == channelEmail {
+		// Reuse the conversation's subject so the code threads into the same email thread instead of
+		// landing in a separate one the customer might reply to.
+		subject := t.conv.Subject.String
+		if subject == "" {
+			subject = t.m.i18n.T("ai.agent.verificationEmailSubject")
+		}
+		sendErr = t.m.convo.SendTransientEmail(t.conv.InboxID, t.conv.ID, t.conv.UUID, []string{email}, subject, body)
+	} else {
+		sendErr = t.m.notifier.Send(notifier.Message{
+			RecipientEmails: []string{email},
+			Subject:         t.m.i18n.T("ai.agent.verificationEmailSubject"),
+			Content:         body,
+			Provider:        notifier.ProviderEmail,
+		})
+	}
+	if sendErr != nil {
+		t.m.lo.Error("error sending verification code email", "conversation_uuid", t.conv.UUID, "error", sendErr)
+		return "", sendErr
 	}
 	t.m.lo.Debug("ai agent sent verification code", "conversation_uuid", t.conv.UUID)
 	return "A verification code has been emailed to the customer. Tell them you have sent a code to their email and ask them to reply with it.", nil

internal/conversation/conversation.go

@@ -1140,6 +1140,27 @@ func (m *Manager) BuildEmailThreadingHeaders(conversationID int, selfSourceID st
 	return references, inReplyTo
 }
 
+// SendTransientEmail sends a one-off email through the conversation's inbox, threaded like a reply, without recording it as a conversation message.
+func (m *Manager) SendTransientEmail(inboxID, conversationID int, conversationUUID string, to []string, subject, htmlContent string) error {
+	inb, err := m.inboxStore.Get(inboxID)
+	if err != nil {
+		return fmt.Errorf("fetching inbox: %w", err)
+	}
+	if inb.Channel() != inbox.ChannelEmail {
+		return fmt.Errorf("cannot send email through non-email inbox %d", inboxID)
+	}
+	references, inReplyTo := m.BuildEmailThreadingHeaders(conversationID, "")
+	return inb.Send(models.OutboundMessage{
+		From:             inb.FromAddress(),
+		To:               to,
+		Subject:          subject,
+		Content:          htmlContent,
+		ConversationUUID: conversationUUID,
+		References:       references,
+		InReplyTo:        inReplyTo,
+	})
+}
+
 // NotifyAssignment sends notifications (in-app, WebSocket, email) for an assigned conversation.
 func (m *Manager) NotifyAssignment(userIDs []int, conversation models.Conversation) error {
 	agent, err := m.userStore.GetAgent(userIDs[0], "")