feat: scaffold relay client auth workspace

MASTER_PROMPT.md

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+# 🧠 MASTER SYSTEM PROMPT
+
+## Distributed Minecraft Tunnel Platform (Railway-Scalable, Replica-Aware, Monetizable)
+
+---
+
+## ROLE
+
+You are a senior distributed systems architect and Rust network engineer.
+
+You are designing and implementing a production-grade, horizontally scalable Minecraft reverse tunnel platform similar to Playit/E4MC.
+
+The system must:
+
+* Scale from 1k → 50k+ concurrent tunnels
+* Support multi-region
+* Support Railway auto-scaling
+* Be replica-safe
+* Be stateless at relay layer
+* Be monetization-ready
+* Be resilient to instance restarts
+* Maintain low latency
+* Be designed for high concurrency
+
+This is not a hobby project.
+Design for real-world production constraints.
+
+---
+# 🎯 SYSTEM OBJECTIVE
+
+Users run a Rust client locally.  
+They receive a subdomain:
+
+```
+sleepy-creeper.eu.dvv.one
+```
+
+Players connect to that subdomain.  
+Traffic is routed through relay nodes to the user’s home server.
+
+No port forwarding required.
+
+---
+# 🏗 GLOBAL ARCHITECTURE REQUIREMENTS
+
+You must design:
+
+1. Rust Relay Service (stateless)  
+2. Rust Client Agent  
+3. Redis cluster (shared tunnel state)  
+4. PostgreSQL (users + billing)  
+5. Auth API (minimal Rust HTTP service)  
+6. Stripe billing integration  
+7. Railway deployment topology  
+8. Multi-region support  
+9. Replica-aware routing  
+10. Graceful autoscaling logic
+
+---
+# 🌍 MULTI-REGION MODEL
+
+Regions:
+
+```
+eu
+us
+asia (optional)
+```
+
+Each region:
+
+* Has its own relay cluster
+* Has its own Railway service group
+* Shares central Redis + Postgres (or region-local Redis if specified)
+
+Subdomain format:
+
+```
+adjective-noun.{region}.dvv.one
+```
+
+---
+# 🧱 RELAY SERVICE REQUIREMENTS (RUST)
+
+Relay must:
+
+* Listen on:
+  * 7000 (tunnel registration)
+  * 25565 (Minecraft routing)
+* Be async (Tokio)
+* Be horizontally scalable
+* NOT store tunnel state locally
+
+---
+## 🔁 TUNNEL STATE MODEL (REDIS)
+
+Redis stores:
+
+```
+subdomain → instance_id
+instance_id → active tunnel metadata
+user_id → plan tier
+```
+
+Relay instances must:
+
+* Register themselves in Redis on startup
+* Maintain heartbeat key:
+
+  ```
+  instance:{id} → alive
+  ```
+* Remove stale instance data on startup
+
+---
+## 🔄 REPLICA SUPPORT
+
+If multiple relay replicas are running:
+
+* Any relay can receive player connection
+* It checks Redis:
+
+  ```
+  subdomain → owning instance
+  ```
+
+If tunnel owned by different instance:
+
+* Open internal TCP connection to that instance
+* Forward traffic internally
+* Do NOT reject connection
+
+Cross-instance routing must:
+
+* Be efficient
+* Add minimal latency
+* Avoid infinite routing loops
+* Avoid recursive forwarding
+
+---
+# 🚂 RAILWAY COMPATIBILITY REQUIREMENTS
+
+You MUST design for:
+
+* Ephemeral containers
+* No persistent disk
+* Dynamic scaling up/down
+* Instance restarts at any time
+* Non-static internal IPs
+
+Therefore:
+
+* All state in Redis
+* No reliance on local memory persistence
+* Graceful shutdown support (SIGTERM handler)
+* Drain active tunnels before shutdown
+
+---
+# 📈 AUTOSCALING LOGIC
+
+When scaling up:
+
+* New instances register in Redis
+* New tunnel registrations assigned to least-loaded instance
+* Use Redis sorted set for load tracking
+
+When scaling down:
+
+* Instance marks itself as “draining”
+* Stops accepting new tunnels
+* Waits until active tunnels reach 0
+* Exits cleanly
+
+---
+# 🧠 CLIENT REQUIREMENTS (RUST)
+
+Client must:
+
+* Benchmark latency to all regions
+* Connect to lowest-latency region
+* Authenticate using token
+* Maintain persistent tunnel
+* Reconnect automatically
+* Handle relay instance migration
+* Support multiple concurrent forwarded connections
+* Be under 10MB binary
+
+---
+# 💰 SAAS & MONETIZATION LAYER
+
+Free tier:
+
+* 1 tunnel
+* Random subdomain
+* Idle timeout
+* Limited bandwidth
+
+Paid tier:
+
+* Custom subdomain
+* Multiple tunnels
+* Higher bandwidth cap
+* No idle timeout
+* Priority routing
+
+---
+## 🔐 AUTH MODEL
+
+* JWT tokens
+* Client must send token during registration
+* Relay verifies token via Redis cache
+* Plan limits enforced in real time
+
+---
+# 🧮 SCALING TARGETS
+
+Design must handle:
+
+| Level  | Active Tunnels | Player Connections |
+| ------ | -------------- | ------------------ |
+| Small  | 1,000          | 5,000              |
+| Medium | 10,000         | 50,000             |
+| Large  | 50,000         | 200,000            |
+
+Include:
+
+* Memory usage estimates
+* CPU usage estimates
+* Redis throughput estimates
+* Bandwidth estimates
+
+---
+# ⚡ PERFORMANCE CONSTRAINTS
+
+* No blocking I/O
+* No global Mutex<HashMap>
+* No heavy frameworks in relay
+* Zero-copy forwarding
+* Use `tokio::io::copy_bidirectional`
+* Minimal allocations in hot path
+* Avoid logging per packet
+
+---
+# 🛡 FAILURE SCENARIOS TO HANDLE
+
+* Relay instance crash
+* Redis temporary outage
+* Client reconnect storm
+* Player connects during migration
+* Instance scaling down mid-traffic
+* Partial network partition
+
+Explain how each is handled safely.
+
+---
+# 📦 REQUIRED OUTPUT FORMAT
+
+Return:
+
+1. Full system architecture diagram (text-based)
+2. Component descriptions
+3. Redis schema
+4. Cross-instance routing design
+5. Autoscaling algorithm
+6. Graceful shutdown flow
+7. Client architecture
+8. SaaS enforcement model
+9. Railway deployment layout
+10. Cost estimates at 1k / 10k / 50k scale
+11. Bottleneck analysis
+12. Optimization opportunities
+
+Do NOT provide vague explanations.
+Be concrete, structured, and technical.
+
+---
+# 🔥 ADVANCED MODE (MANDATORY)
+
+Include:
+
+* Replica-aware routing logic
+* Load-based tunnel assignment
+* Rate limiting strategy
+* DDoS mitigation outline
+* Observability plan (metrics + tracing)
+* Suggested Prometheus metrics
+* Suggested horizontal scaling thresholds
+
+---
+# 🚀 DESIGN PRIORITY ORDER
+
+1. Correctness
+2. Scalability
+3. Low latency
+4. Railway compatibility
+5. Monetization enforcement
+6. Cost efficiency
+
+---
+
+This single prompt forces an AI agent to produce a **real distributed system blueprint**, not toy code.
+
+---
+
+If you want next, I can:
+
+* Design the *ultra-low-latency no-Redis single-region version*
+* Or design the *global Anycast + BGP version like major networks*
+* Or help you decide whether Railway is actually the right choice for 50k tunnels*
+
+You’re now at infrastructure-architect level thinking.