# E2.M2 — XpAwardAndLevelEngine

## Summary

| Field | Value |
|--------|--------|
| **Module ID** | E2.M2 |
| **Epic** | [Epic 2 — Classless Progression](../epics/epic_02_classless_progression.md) |
| **Stage target** | Prototype |
| **Status** | Planned (see [dependency register](module_dependency_register.md)) |

## Purpose

Central server-authoritative engine for classless skill progression: applying XP grants, resolving levels against data-driven curves, and emitting level-up events. Gathering, crafting, and combat integrate **as callers** of this API without being hard dependencies for implementing the engine itself (see Epic 2 Slice 2 vs Slice 3).

## Responsibilities

- Apply `XpGrantEvent` (or equivalent) per skill with validated skill references from [E2.M1](E2_M1_SkillDefinitionRegistry.md).
- Resolve experience against `LevelCurve` / threshold tables.
- Emit `LevelUpEvent` when thresholds are crossed.
- Support data-driven curves and reload policy agreed for prototype.

## Key contracts

| Contract | Role |
|----------|------|
| `XpGrantEvent` | Structured XP award (skill id, amount, source, modifiers). |
| `LevelCurve` | Thresholds or formula per skill or global policy. |
| `LevelUpEvent` | Notification for UI, unlocks, and downstream systems. |

## Module dependencies

- **E2.M1** — [SkillDefinitionRegistry](E2_M1_SkillDefinitionRegistry.md): `SkillDef`, categories, and validation of skill IDs.

## Dependents (by design)

- **E5.M1** — CombatRulesEngine: combat awards XP via integration (Epic 5 / Epic 2 slices).
- **E3.M1 / E3.M2** — Gathering and crafting award XP when wired in Slice 3.
- **E7.M2** — RewardAndUnlockRouter routes quest rewards including XP through E2.M2.
- **E2.M3 / E2.M4** — Mastery and pacing layers build on level/XP state (pre-production).

## Related implementation slices

- **Epic 2 Slice 2 — XP engine (E2.M2 core)**: implement contracts and tests without requiring Epic 3 or 5 modules.
- **Epic 2 Slice 3 — XP award integration**: wire E3.M1, E3.M2, E5.M1 to the award API for three prototype skill lines.

## Risks and telemetry

- Runaway leveling in one skill: diminishing returns per slice; monitor distribution via E9.M2 when available.
- Telemetry: `xp_grant`, `level_up`, time-to-first-level-up once real activity fires.

## Source anchors

- Master plan: [`neon_sprawl_vision.plan.md`](../../../neon_sprawl_vision.plan.md) — Core Epic Map, Epic 2.
- [Module dependency register](module_dependency_register.md)