docs: sync from backend cab0719 - align request budget validation

00 - Overview/System Overview.md

@@ -14,7 +14,7 @@ created: 2026-05-23
 Amn is a **two-repo system**:
 
 - **Frontend** (`/Users/mojtabaheidari/code/frontend`) — a Next.js 16 App Router application that serves the marketplace UI, the admin dashboard, the public blog, and the user-facing Web3 wallet flow.
-- **Backend** (`/Users/mojtabaheidari/code/backend`) — an Express 5 + TypeScript API server that owns all business logic, persists to MongoDB, caches in Redis, and brokers all external integrations.
+- **Backend** (`/Users/mojtabaheidari/code/backend`) — an Express 5 + TypeScript API server that owns all business logic, persists live app state primarily to MongoDB, caches in Redis, and brokers all external integrations. The active integration backend also contains the Postgres/Drizzle migration layer, but it is not yet the broad runtime store.
 
 The two repos are deployable independently. They communicate over **HTTPS (REST)** for stateful actions and over **WebSocket (Socket.IO)** for live updates. The frontend never talks directly to MongoDB, Redis, Request Network API keys, OpenAI, or admin custody secrets -- every sensitive external interaction is mediated by the backend so that secrets stay on the server.
 
@@ -52,7 +52,8 @@ flowchart TB
     end
 
     subgraph Data["Data tier"]
-        Mongo[("MongoDB<br/>via Mongoose")]
+        Mongo[("MongoDB<br/>via Mongoose<br/>primary runtime")]
+        PG[("PostgreSQL 18<br/>Drizzle migration layer")]
         RedisDB[("Redis<br/>cache + locks")]
         Disk[("Local disk<br/>/uploads")]
     end
@@ -84,6 +85,7 @@ flowchart TB
     SocketS --> ChatSvc & Notif & Market
 
     Auth & Market & ChatSvc & PaySvc & Disp & Points & BlogSvc & TelegramSvc --> Mongo
+    PaySvc -.->|oracle payment_quotes when enabled| PG
     Auth & PaySvc & Notif --> RedisDB
     Files --> Disk
 
@@ -135,6 +137,7 @@ Payments are where Amn is most distinctive. The live backend has converged on **
 - **Derived destination wallets** -- `/api/payment/derived-destinations` admin endpoints manage per-`(buyer, sellerOffer, chainId)` receiving addresses, sweep status, and config health.
 - **Funds ledger** -- `backend/src/services/payment/ledger/` tracks payment detection, holds, releases, refunds, fees, and adjustments independently of provider metadata.
 - **Release/refund orchestration** -- `/api/payment/:id/(release|refund)` builds instructions; `/confirm` records confirmed transaction hashes. Optional Trezor enforcement gates confirmation when `TREZOR_SAFEKEEPING_REQUIRED=true`.
+- **Postgres migration layer** -- backend `2.6.79` includes Drizzle migrations/repos and can persist oracle quote rows to `payment_quotes` when enabled. Payment records, ledger state, wallet destinations, and marketplace entities still flow through Mongo-backed services until the cutover work in [[Postgres Runtime Cutover Status]] is completed.
 
 Historical SHKeeper and DePay docs remain in the vault for migration context, but the current backend tree no longer has `backend/src/services/payment/shkeeper/`. The current strategic path is in [[PRD - Decentralized Custody and Smart-Contract Escrow Roadmap]].