feat(billing): usage-rating + webhook-dispatch crons

- SaleOrder._fc_rate_usage: aggregates usage, computes overage via
  charge._compute_billable, upserts sale.order.line for the overage product
- FusionBillingUsage._cron_rate_open_periods: hourly cron iterates active
  charges × in-progress subscriptions, calls _fc_rate_usage
- data/ir_cron.xml: two crons — rate usage (hourly), dispatch webhooks (2 min)
- __manifest__.py: registers data/ir_cron.xml in data list
- test_usage.py: test_rate_open_period_creates_overage_line (TDD, FCB_EXIT=0)

Reference: _create_recurring_invoice / _get_invoiceable_lines confirmed in
Enterprise sale_subscription/models/sale_order.py — overage line goes onto
sale.order so native invoicing picks it up via _get_invoiceable_lines.

fusion_centralize_billing/__manifest__.py

@@ -47,6 +47,7 @@ reference files from the container before implementing subscription/account inte
     ],
     "data": [
         "security/ir.model.access.csv",
+        "data/ir_cron.xml",
     ],
     "installable": True,
     "application": False,

fusion_centralize_billing/data/ir_cron.xml

@@ -0,0 +1,22 @@
+<?xml version="1.0" encoding="utf-8"?>
+<odoo noupdate="1">
+    <record id="cron_fc_rate_usage" model="ir.cron">
+        <field name="name">Fusion Billing: Rate usage before invoicing</field>
+        <field name="model_id" ref="model_fusion_billing_usage"/>
+        <field name="state">code</field>
+        <field name="code">model._cron_rate_open_periods()</field>
+        <field name="interval_number">1</field>
+        <field name="interval_type">hours</field>
+        <field name="active">True</field>
+    </record>
+
+    <record id="cron_fc_dispatch_webhooks" model="ir.cron">
+        <field name="name">Fusion Billing: Dispatch outbound webhooks</field>
+        <field name="model_id" ref="model_fusion_billing_webhook"/>
+        <field name="state">code</field>
+        <field name="code">model._cron_dispatch()</field>
+        <field name="interval_number">2</field>
+        <field name="interval_type">minutes</field>
+        <field name="active">True</field>
+    </record>
+</odoo>

fusion_centralize_billing/models/__init__.py

@@ -5,3 +5,4 @@ from . import charge
 from . import usage
 from . import webhook
 from . import reconciliation
+from . import sale_order

fusion_centralize_billing/models/sale_order.py

@@ -0,0 +1,26 @@
+# -*- coding: utf-8 -*-
+# Copyright 2026 Nexa Systems Inc.
+# License OPL-1
+from odoo import api, fields, models
+
+
+class SaleOrder(models.Model):
+    _inherit = "sale.order"
+
+    def _fc_rate_usage(self, charge, period_start, period_end):
+        """Aggregate this subscription's usage for `charge`'s metric in the period,
+        compute the overage amount, and upsert a matching overage order line.
+        Returns the amount."""
+        self.ensure_one()
+        Usage = self.env['fusion.billing.usage']
+        total = Usage._aggregate(self, charge.metric_id, period_start, period_end)
+        _overage, amount = charge._compute_billable(total)
+        if charge.product_id:
+            line = self.order_line.filtered(lambda l: l.product_id == charge.product_id)
+            vals = {'product_uom_qty': 1, 'price_unit': amount}
+            if line:
+                line.write(vals)
+            else:
+                self.env['sale.order.line'].create(
+                    {'order_id': self.id, 'product_id': charge.product_id.id, **vals})
+        return amount

fusion_centralize_billing/models/usage.py

@@ -59,6 +59,25 @@ class FusionBillingUsage(models.Model):
                 return existing
         return self.create(vals)
 
+    @api.model
+    def _cron_rate_open_periods(self):
+        """Hourly cron: for every active charge, aggregate usage and upsert overage lines
+        on all in-progress subscriptions whose next invoice date is set."""
+        Charge = self.env['fusion.billing.charge'].search([('active', '=', True)])
+        SaleOrder = self.env['sale.order']
+        for charge in Charge:
+            subs = SaleOrder.search([
+                ('is_subscription', '=', True),
+                ('subscription_state', '=', '3_progress'),
+                ('plan_id.name', '!=', False),
+            ])
+            for sub in subs:
+                if not sub.next_invoice_date:
+                    continue
+                period_end = fields.Datetime.to_datetime(sub.next_invoice_date)
+                period_start = period_end.replace(day=1)
+                sub._fc_rate_usage(charge, period_start, period_end)
+
     @api.model
     def _aggregate(self, subscription, metric, period_start, period_end):
         """Aggregate stored usage for a subscription+metric within [period_start, period_end)

fusion_centralize_billing/tests/test_usage.py

@@ -50,3 +50,18 @@ class TestUsageIngestion(TransactionCase):
         self.Usage._record_usage(self.sub, 'cpu_seconds', 99.0, '2026-04-01', '2026-05-01', idem='apr')
         self.Usage._record_usage(self.sub, 'cpu_seconds', 5.0, '2026-05-01', '2026-06-01', idem='may')
         self.assertEqual(self.Usage._aggregate(self.sub, self.metric, '2026-05-01', '2026-06-01'), 5.0)
+
+    def test_rate_open_period_creates_overage_line(self):
+        product = self.env['product.product'].sudo().create(
+            {'name': 'API overage', 'type': 'service', 'list_price': 0.0})
+        charge = self.env['fusion.billing.charge'].sudo().create({
+            'name': 'overage', 'plan_code': 'p', 'metric_id': self.metric.id,
+            'product_id': product.id, 'included_quota': 100.0,
+            'price_per_unit': 0.10, 'unit_batch': 1000.0, 'charge_model': 'standard'})
+        self.Usage._record_usage(self.sub, 'cpu_seconds', 1100.0,
+                                 '2026-05-01', '2026-06-01', idem='r1')
+        amount = self.sub._fc_rate_usage(charge, '2026-05-01', '2026-06-01')
+        # 1100 - 100 = 1000 overage = 1 batch * $0.10 = $0.10
+        self.assertAlmostEqual(amount, 0.10, places=2)
+        line = self.sub.order_line.filtered(lambda l: l.product_id == product)
+        self.assertTrue(line)