feat(billing): /usage resolves subscription by source app id (enables 2b)

_api_record_usage now resolves the target subscription via the source
app's own id (x_fc_nexacloud_subscription_id, scoped to the service)
before falling back to a direct Odoo sale.order id. This is what lets
NexaCloud push usage against the shadow subscriptions the importer
created from NexaCloud UUIDs — closing the flip-day mapping gap the
review flagged. Authz unchanged (partner must be linked to the service).

fusion_centralize_billing/models/service.py

@@ -109,6 +109,27 @@ class FusionBillingService(models.Model):
             self, ext, name=payload.get('name'), email=payload.get('email'))
         return {'status': 'ok', 'partner_id': link.partner_id.id, 'external_id': ext}
 
+    def _fc_resolve_subscription(self, external_ref):
+        """Resolve the subscription sale.order a usage event targets.
+
+        Prefer the source app's OWN id (``x_fc_nexacloud_subscription_id`` scoped to this
+        service) so apps reference their own ids — this is what lets NexaCloud push usage
+        against shadow subscriptions the importer created from its UUIDs. Falls back to a
+        direct Odoo ``sale.order`` id for live-created subs (post-flip). Authorization is
+        still enforced by the caller (partner must be linked to this service)."""
+        self.ensure_one()
+        SaleOrder = self.env['sale.order']
+        sub = SaleOrder.search([
+            ('x_fc_nexacloud_subscription_id', '=', str(external_ref)),
+            ('x_fc_billing_service_id', '=', self.id),
+        ], limit=1)
+        if sub:
+            return sub
+        try:
+            return SaleOrder.browse(int(external_ref))
+        except (TypeError, ValueError):
+            return SaleOrder
+
     def _api_record_usage(self, payload):
         """Ingest a batch of usage events.
 
@@ -139,15 +160,11 @@ class FusionBillingService(models.Model):
                         'period_start', 'period_end'):
                 if ev.get(key) in (None, ''):
                     return {'status': 'error', 'error': 'missing %s' % key}
-            try:
-                sub_id = int(ev['subscription_external_id'])
-            except (TypeError, ValueError):
-                return {'status': 'error', 'error': 'invalid subscription_external_id'}
             try:
                 quantity = float(ev['quantity'])
             except (TypeError, ValueError):
                 return {'status': 'error', 'error': 'invalid quantity'}
-            sub = self.env['sale.order'].browse(sub_id)
+            sub = self._fc_resolve_subscription(ev['subscription_external_id'])
             if not sub.exists() or not sub.is_subscription \
                     or sub.partner_id not in linked_partners:
                 return {'status': 'error', 'error': 'unknown subscription'}

fusion_centralize_billing/tests/test_importer.py

@@ -254,3 +254,26 @@ class TestImporterReadGuard(TransactionCase):
         wiz = self.env['fusion.billing.import.wizard'].sudo().create({'dry_run': True})
         with self.assertRaises(UserError):
             wiz.action_test_connection()
+
+
+@tagged('post_install', '-at_install')
+class TestUsageApiSourceId(TransactionCase):
+    """The /usage API must resolve a subscription by NexaCloud's OWN id, so usage can be
+    pushed against shadow subs the importer created from UUIDs (the flip-day gap)."""
+
+    def setUp(self):
+        super().setUp()
+        self.env['fusion.billing.import.wizard'].sudo()._import_rows(_fixture())
+        self.service = self.env['fusion.billing.service'].search([('code', '=', 'nexacloud')])
+
+    def test_record_usage_resolves_by_nexacloud_subscription_id(self):
+        res = self.service._api_record_usage({'events': [{
+            'subscription_external_id': 's-1',   # NexaCloud UUID, not the Odoo id
+            'metric_code': 'cpu_seconds', 'quantity': 3600.0,
+            'period_start': '2026-05-01', 'period_end': '2026-06-01',
+            'idempotency_key': 'nc:s-1:2026-05'}]})
+        self.assertEqual(res['status'], 'ok')
+        self.assertEqual(res['accepted'], 1)
+        sub = self.env['sale.order'].search([('x_fc_nexacloud_subscription_id', '=', 's-1')])
+        usage = self.env['fusion.billing.usage'].search([('subscription_id', '=', sub.id)])
+        self.assertEqual(usage.quantity, 3600.0)