diff --git a/database-novo/migrations/20260423000004_whatsapp_low_balance_notify.sql b/database-novo/migrations/20260423000004_whatsapp_low_balance_notify.sql
new file mode 100644
index 0000000..8ea04e7
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+++ b/database-novo/migrations/20260423000004_whatsapp_low_balance_notify.sql
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+-- ==========================================================================
+-- Agencia PSI — Migracao: Alerta de saldo baixo WhatsApp
+-- ==========================================================================
+-- Criado por: Leonardo Nohama
+-- Data: 2026-04-23 · Sao Carlos/SP — Brasil
+--
+-- Fecha o loop do Marco B: tenant compra creditos → usa → saldo zera sem
+-- aviso → PIX recusado surpresa. Agora o tenant e admins recebem
+-- notificacao quando saldo cai abaixo do threshold configurado.
+--
+-- Modelo:
+--   - whatsapp_credits_balance ja tem:
+--       low_balance_threshold (default 20)
+--       low_balance_alerted_at (anti-spam; reset via add_whatsapp_credits)
+--   - Falta so o trigger que dispara a notificacao.
+--
+-- Fluxo:
+--   1. UPDATE em whatsapp_credits_balance (via deduct/adjust)
+--   2. Trigger BEFORE UPDATE detecta balance < threshold E alerted_at IS NULL
+--   3. Insere system_alert pros stakeholders (owner do canal WhatsApp
+--      ativo + clinic_admin + tenant_admin do tenant, deduplicado)
+--   4. Seta NEW.low_balance_alerted_at = now() pra nao realertar
+--   5. Reset do alerted_at acontece em add_whatsapp_credits / topup
+--      (ja existe: "low_balance_alerted_at = NULL" na RPC)
+-- ==========================================================================
+
+CREATE OR REPLACE FUNCTION public.fn_whatsapp_low_balance_notify()
+RETURNS TRIGGER
+LANGUAGE plpgsql
+SECURITY DEFINER
+SET search_path = public
+AS $$
+DECLARE
+    v_detail TEXT;
+BEGIN
+    -- So alerta na transicao (alerted_at NULL) E se esta abaixo do threshold
+    IF NEW.balance < NEW.low_balance_threshold
+       AND NEW.low_balance_alerted_at IS NULL THEN
+
+        v_detail := format(
+            'Saldo atual: %s credito(s). Alerta configurado em %s. '
+            'Compre mais na loja para nao interromper envios via WhatsApp Oficial.',
+            NEW.balance,
+            NEW.low_balance_threshold
+        );
+
+        -- Stakeholders: owner do canal WhatsApp ativo + admins ativos do tenant
+        INSERT INTO public.notifications
+            (owner_id, tenant_id, type, ref_id, ref_table, payload)
+        SELECT
+            u.user_id,
+            NEW.tenant_id,
+            'system_alert',
+            NEW.tenant_id,
+            'whatsapp_credits_balance',
+            jsonb_build_object(
+                'title', 'Saldo de WhatsApp baixo',
+                'detail', v_detail,
+                'severity', 'warn',
+                'deeplink', '/configuracoes/creditos-whatsapp'
+            )
+        FROM (
+            SELECT owner_id AS user_id
+                FROM public.notification_channels
+                WHERE tenant_id = NEW.tenant_id
+                  AND channel = 'whatsapp'
+                  AND is_active = true
+                  AND deleted_at IS NULL
+            UNION
+            SELECT user_id
+                FROM public.tenant_members
+                WHERE tenant_id = NEW.tenant_id
+                  AND role IN ('clinic_admin', 'tenant_admin')
+                  AND status = 'active'
+        ) u
+        WHERE u.user_id IS NOT NULL;
+
+        -- Anti-spam: so alerta de novo depois que add_whatsapp_credits
+        -- reseta alerted_at pra NULL (acontece em purchase/topup)
+        NEW.low_balance_alerted_at := now();
+    END IF;
+
+    RETURN NEW;
+END;
+$$;
+
+COMMENT ON FUNCTION public.fn_whatsapp_low_balance_notify() IS
+    'Trigger BEFORE UPDATE em whatsapp_credits_balance. Dispara notificacao system_alert quando saldo cruza low_balance_threshold pra baixo. Anti-spam via low_balance_alerted_at (resetado pelo add_whatsapp_credits).';
+
+DROP TRIGGER IF EXISTS trg_whatsapp_low_balance_notify
+    ON public.whatsapp_credits_balance;
+
+CREATE TRIGGER trg_whatsapp_low_balance_notify
+    BEFORE UPDATE ON public.whatsapp_credits_balance
+    FOR EACH ROW
+    EXECUTE FUNCTION public.fn_whatsapp_low_balance_notify();