# E4.M3 — SeamlessHandoffAndRegionState

## Summary

| Field | Value |
|--------|--------|
| **Module ID** | E4.M3 |
| **Epic** | [Epic 4 — World Topology](../epics/epic_04_world_topology.md) |
| **Stage target** | Pre-production |
| **Status** | Planned (see [dependency register](module_dependency_register.md)) |

## Purpose

Cross-region handoff behavior and region authority boundaries. Minimal spike: two regions with authority transfer and no duplicate entities.

**Epic note:** Depends on **backend world services** in addition to E4.M1; those integrations are out-of-repo contracts until defined.

## Responsibilities

- Orchestrate `RegionHandoffEvent`; model `RegionAuthority` and `TransferState` during handoff.

## Key contracts

| Contract | Role |
|----------|------|
| `RegionHandoffEvent` | Start/complete/fail lifecycle. |
| `RegionAuthority` | Which service owns simulation for an entity. |
| `TransferState` | Serializable handoff payload. |

## Module dependencies

- **E4.M1** — ZoneGraphAndTravelRules.

## Dependents (by design)

- World/shard services (external); client runtime for loading/streaming.

## Related implementation slices

Epic 4 **Slice 4** — `region_handoff_start`, `region_handoff_complete`, rollback path documented.

## Source anchors

- Master plan: [`neon_sprawl_vision.plan.md`](../../../neon_sprawl_vision.plan.md) — Epic 4.
- [Module dependency register](module_dependency_register.md)
