Ymir Architecture

Objective

Own physics for Aetheria outside Unity so projectiles, fields, bodies, and contacts share one simulation truth across game runtime, server logic, tools, and future Verse surfaces.

Current Mechanism

The MVP has one pure core and one daemon:

Ymir.Core receives a YmirSoAWorld and a fixed deltaTime.
Compatibility callers may still submit a YmirWorld, but it is immediately lowered into SoA buffers before simulation.
The core computes radial field acceleration with CultMath BatchMath, uses vectorized semi-implicit Euler integration over SoA arrays, tests circle overlaps, resolves simple collision response, and emits contact events.
ymir-daemon publishes provider/operator state and exposes the core through a small HTTP compatibility surface.
YmirWorldStateDocument persists the same SoA world as gamecult.ymir.world_state.v0 through CultCache MessagePack.

Owner

Ymir owns the decision: given world state plus a time step, what is the next physics state and which contacts occurred.

Inputs

SoA body columns: id, position x/y, velocity x/y, radius, mass, dynamic mask, restitution
SoA radial field columns: id, position x/y, strength, radius
fixed deltaTime

Outputs

next world time
next body positions and velocities
contact events with body ids, point, normal, penetration, and relative speed

Derived State

YmirWorld DTO records are compatibility views over YmirSoAWorld.
HTTP health, provider advertisement, operator state, and Eve surface are derived compatibility views.
Unity GameObjects are derived render/adapter state.
Damage events in Aetheria should become derived from Ymir contacts plus Aetheria gameplay policy.

Forbidden Writers

Unity OnCollisionEnter and collider callbacks must stop deciding projectile hit truth once a cutover path exists.
Renderer transforms must not push hidden physics corrections back into Ymir.
HTTP compatibility witnesses must not become durable state owners.

Shared Paths

Direct user actions, weapon firing, programmatic spawns, reloads, server ticks, and replay/import paths should all create or modify Ymir world state through the same command/step primitive. Manual Unity interaction may author inputs; it does not become a second simulation.

Cut Line

The old Aetheria projectile GameObject/collider path is demoted first to a renderer and diagnostic witness. New damage or hit policy must consume Ymir contact events. Only after that path is proven should Unity collider callbacks be deleted.

Verification Layer

Unit tests prove core integration, gravity field acceleration, deterministic ordering, and contact generation.
CLI smoke proves the daemon can execute a step without booting Unity.
Aetheria cutover needs a Unity-side timeline probe that compares visible projectile positions and hit events against Ymir snapshots during travel, not only after impact.

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