feat(integration): prepaid billing, engine UI, credits console, direct tasks, v2 final

- Prepaid credit system: org wallet, debit on usage, chat gate, admin credit console
- Engine UI: /manager, /tasks, /tasks/[id], /workforce, /dashboard, /traces pages
- Direct task creation (HTTP POST /tasks, MCP tasks_create) at pending_manager_review
- Pause/resume/cancel/answer actions in engine API and UI
- Employee cap (7 per org default), review pipeline guard (active reviewer required)
- Scheduler: wide window prevents org starvation; archived employees excluded from cap
- Tenant isolation: project-id cross-org 404, engine never uses another tenant's sandbox
- Order route fix: manager built with pipeline states + employee profiles
- Contract extension: ModelGrantPort.get_org_policy with DefaultOrgPolicy
- Engine event types in @agy/contracts (task.step, task.gate, run.log, run.tool, team.changed)
- api-engine.ts typed client; api-credit.ts client
- Alembic migration c4d5e6f7a8b9: prepaid credit + engine UI tables
- 859 tests passed, 1 skipped; ruff/mypy/tsc/eslint/vitest all green

Refs: PLAN-v2.md §9 (T1–T43), todo-v2-final.md

apps/api/app/application/services/billing_service.py

@@ -17,6 +17,7 @@ from app.application.ports import PaymentProviderPort
 from app.application.ports.realtime import emit_wallet_changed
 from app.core.errors import NotFoundError, PermissionDeniedError, ValidationError
 from app.domain.billing.models import (
+    CreditKind,
     CreditWallet,
     Invoice,
     Payment,
@@ -31,6 +32,7 @@ from app.infrastructure.repositories.billing import (
     PlanRepository,
     SubscriptionRepository,
 )
+from app.infrastructure.repositories.credit import CreditLedgerRepository
 
 #: A tenant may not buy an arbitrary amount of credit in one action.
 MIN_TOPUP = 1.0
@@ -56,6 +58,8 @@ class BillingService:
         self.subscriptions = subscriptions
         self.ledger = ledger
         self.payment_provider = payment_provider
+        # Settled payments are credited through the credit ledger, in the wallets' session.
+        self.credit_ledger = CreditLedgerRepository(wallets.session)
 
     # -- reads ---------------------------------------------------------------
 
@@ -107,6 +111,8 @@ class BillingService:
     ) -> CreditWallet:
         """Grant (or, for a platform owner, claw back) credit.
 
+        Superseded by the owner-only ``CreditService``, which writes the credit ledger.
+
         ``allow_negative`` is reserved for the platform owner console; an org
         admin may only ever add credit.
         """
@@ -171,7 +177,9 @@ class BillingService:
 
         This is the only path that turns money into credit, so it is idempotent
         with respect to status: a payment that is already final is returned
-        untouched rather than credited twice.
+        untouched rather than credited twice. The credit is one ``adjustment`` row in
+        the credit ledger, written in this session, so it shows in the owner's credit
+        history and updates ``last_credit_at``.
         """
         payment = next(
             (p for p in await self.payments.list_for_org(organization_id) if p.id == payment_id),
@@ -183,12 +191,15 @@ class BillingService:
             return payment
 
         if succeeded:
-            wallet = await self.wallets.adjust(
-                organization_id=organization_id, delta=payment.amount
+            credit = await self.credit_ledger.apply(
+                organization_id=organization_id,
+                amount=payment.amount,
+                kind=CreditKind.ADJUSTMENT,
+                reason="billing/settle-payment",
             )
             final = await self.payments.set_status(payment_id, PaymentStatus.SUCCEEDED)
             await emit_wallet_changed(
-                organization_id=organization_id, balance=wallet.balance
+                organization_id=organization_id, balance=credit.balance_after
             )
         else:
             final = await self.payments.set_status(payment_id, PaymentStatus.FAILED)