docs: sync from backend cab0719 - align request budget validation

01 - Architecture/System Architecture.md

@@ -22,7 +22,8 @@ flowchart LR
     Nginx[Nginx Reverse Proxy<br/>:80/:443]
     FE[Next.js Frontend<br/>standalone server<br/>:8083]
     BE[Express Backend<br/>+ Socket.IO<br/>:5001]
-    Mongo[(MongoDB 8)]
+    Mongo[(MongoDB 8<br/>primary runtime store)]
+    PG[(PostgreSQL 18<br/>migration target / quote table)]
     Redis[(Redis 8)]
     RN[Request Network<br/>Pay-in + webhooks]
     CFWorker[Durable webhook ingress<br/>roadmap]
@@ -37,6 +38,7 @@ flowchart LR
     FE -->|REST /api/*| BE
     FE -.->|Socket.IO| BE
     BE --> Mongo
+    BE -.->|PG_URL + migration/quote paths| PG
     BE --> Redis
     BE -->|Pay-in intent / status| RN
     RN -.->|Signed webhook| CFWorker
@@ -79,6 +81,9 @@ sequenceDiagram
     FE-->>U: UI re-render
 ```
 
+> [!note] Postgres status on `integrate-main-into-development`
+> Backend `2.6.79` includes Drizzle schemas, migrations, repository implementations, backfill/verify tooling, and conditional oracle quote persistence to Postgres. It is not a full runtime cutover: ordinary services still call Mongoose models directly and MongoDB remains the primary store. See [[Postgres Runtime Cutover Status]] for the current boundary.
+
 Concurrent realtime path:
 
 ```mermaid
@@ -106,6 +111,7 @@ Production runs as a single Docker Compose stack (`backend/docker-compose.produc
 | App | Frontend | `nickapp-frontend:latest` | 8083 (internal) | Next.js standalone |
 | App | Backend | `nickapp-backend:latest` | 5001 (internal) | Express + Socket.IO |
 | Data | MongoDB | `mongo:8.0` | 27017 (internal) | Primary store |
+| Data | PostgreSQL | `postgres:18` / `postgres:18-alpine` | 5432 (internal) | Migration target; required for PG backfill/verify and oracle `payment_quotes` when enabled |
 | Data | Redis | `redis:8-alpine` | 6379 (internal) | Cache + sessions + rate-limit counters |
 
 External SSL termination, DNS, and CDN are assumed to live in front of Nginx (CloudFlare / nginx-proxy / similar).
@@ -176,6 +182,7 @@ See [[PRD - Request Network In-House Checkout]] and [[Request Network Integratio
 |---|---|---|
 | Backend stateless? | Yes — JWT-only auth, no in-memory session | Run N replicas behind LB; use Redis pub/sub adapter for Socket.IO |
 | MongoDB | Single-node | Replica set → sharding by `buyerId` |
+| PostgreSQL | Dev/staging service for migration work | Managed Postgres or hardened self-hosted PG with backups/PITR before cutover |
 | Redis | Single-node | Cluster mode; separate cache vs session DBs |
 | Socket.IO | Single process | `@socket.io/redis-adapter` for multi-node fan-out |
 | File uploads | Local `uploads/` mount | S3 / R2; multer-s3 adapter |