# ADR-0008: Border strategy — session migration / portals

- **Status:** Accepted
- **Date:** 2026-07-30

## Context

A single global authoritative Minecraft simulation across many peers is unrealistic at scale (tick rate, redstone, entity AI, bandwidth). Full chunk CRDTs are also impractical for real-time play.

## Decision

**Coordinate-space federation** with **session migration**:

1. Each peer owns a region with bounds/offset.
2. Near border: plugin triggers portal or auto-migrate.
3. Serialize player state; Protomux `flying-jib/migrate` handoff.
4. Guest switches HyperDHT tunnel to neighbor `worldKey` and reconnects Java to localhost.
5. Spawn at mapped coordinates.

**Not in v1:** streaming foreign chunks into the local Squid world or dual-sim entity forwarding.

Later phases may add interest-based border sync without abandoning local authority.

## Consequences

### Positive

- Feasible engineering path
- Clear failure mode when neighbor offline
- Preserves Squid as sole authority per region

### Negative / tradeoffs

- Reconnect hitch at borders
- Inventory race risks (must two-phase commit — Q6)
- Not perfectly seamless vanilla continuous terrain

### Follow-ups

- [ ] Phase 4 plugins + migrate state machine
- [ ] Resolve Q6 with tests