# render actual message content per sample
    engine = VariableEngine(c.variable_config or {})
    out = []
    for item in plan:
        rec = next((r for r in recipient_rows if r.id == item["recipient_id"]), None)
        if not rec:
            continue
        tpl = await db.get(EmailTemplate, item["template_id"]) if item.get("template_id") else None
        subj = await db.get(SubjectLine, item["subject_id"]) if item.get("subject_id") else None
        g = GeneratedValues()
        g.invoice_number = item.get("invoice_number", "")
        g.amount = item.get("amount")
        g.shipping = item.get("shipping")
        g.invoice_date = item.get("invoice_date")
        g.due_date = item.get("due_date")
        phone = item.get("phone", "")
        unsub = f"{cfg.UNSUBSCRIBE_BASE or cfg.BASE_URL}/unsubscribe/{rec.unsub_token}" if c.unsubscribe_enabled else ""
        extra = {"unsubscribe_link": unsub, "company_phone": phone}

        body_html = ""
        subject = ""
        warn_list = list(item.get("warnings") or []) if isinstance(item.get("warnings"), list) else ([item["warnings"]] if item.get("warnings") else [])
        if tpl:
            res = engine.substitute(tpl.body_html, rec, g,
                                    custom_fields=rec.custom_fields or {}, extra=extra)
            body_html = res.text
            subject = subj.subject if subj else (tpl.subject_hint or tpl.name)
            for u in res.unknown:
                warn_list.append(f"Unknown variable in body: {u}")
            for m_ in res.missing:
                warn_list.append(f"Missing data for: {m_}")
        if subj:
            res_s = engine.substitute(subj.subject, rec, g,
                                      custom_fields=rec.custom_fields or {}, extra=extra)
            subject = res_s.text
            for u in res_s.unknown:
                warn_list.append(f"Unknown variable in subject: {u}")
            for m_ in res_s.missing:
                warn_list.append(f"Missing data in subject: {m_}")
        out.append({
            "recipient": {"id": rec.id, "email": rec.email,
                          "first_name": rec.first_name, "last_name": rec.last_name},
            "from_account": item.get("account", ""),
            "subject": subject,
            "body_html": sanitize_preview(body_html),
===== send engine subject =====
app/tasks/send_tasks.py:144:        subject_row = db.get(SubjectLine, cr.generated_subject_id) if cr.generated_subject_id else None
app/tasks/send_tasks.py:146:        subject = subject_row.subject if subject_row else campaign.name
app/tasks/send_tasks.py:214:            subject=subject,
app/tasks/send_tasks.py:219:            unsubscribe_mailto=f"{account.email}?subject=unsubscribe",
app/tasks/send_tasks.py:242:            subject=subject,