Ymir

Ymir is the GameCult Box3D wrapper and physics-daemon boundary for Aetheria and future world-bearing projects. The name means Not Invented Here. We are taking the hint.

Box3D owns physics algorithms. Ymir owns the service boundary that makes those algorithms usable as durable, typed GameCult world truth. Unity, renderers, and game products consume Ymir state and contact facts; they do not become physics authorities.

Ownership

• Box3D owns rigid-body integration, collision geometry, broadphase, solver behavior, continuous collision, overlap and cast semantics, contact lifecycle, force and torque lifetime, tolerances, and deterministic step behavior for identical recorded inputs.
• Ymir currently owns the pinned Box3D version, stable GameCult entity ids, native ABI isolation, snapshot lowering, deterministic result ordering, versioned CultCache snapshots, and a diagnostic Eve publication.
• The Ymir daemon will own long-lived world sessions, typed commands and receipts, contact lifecycle facts, checkpoint reconstruction, CultMesh publication, and process supervision. Those are the cutover contract, not a claim that the current CLI already exposes them.
• Aetheria owns gameplay policy and supplies typed physical intent: bodies, fields, tractor targets, forces, projectiles, filters, and the gameplay consequences of Ymir contact facts.
• CultMath remains available for GameCult-side numeric projections and force preparation. It is not a second collision or integration engine.
• Unity and Eve lowerers render world state and submit commands. They never repair, override, or independently simulate authoritative physics.

Box3D opaque handles are process-local derived state. They are never durable entity ids and never cross the public contract boundary.

Current Cutover State

Box3D v0.1.0 is pinned at commit 8441b4a06d6d09dcfb0b0f704df4d847d1437b92. A Ymir-owned native shim and parity suite already witness released Box3D behavior for:

• sphere overlap and shape casts
• tractor capsule membership and rounded caps
• numeric overlap and cast slop
• planar sphere-world stepping
• contact-begin facts
• restitution mixing
• transient torque lifetime

The production Ymir.Box3D boundary owns the native session ABI. The legacy snapshot YmirSimulator.Step contract now creates an isolated Box3D session, projects the result, and disposes it. It contains no managed integrator, collision loop, or impulse solver.

That snapshot facade deliberately does not pretend to own long-lived world identity. The retained native session exists behind an internal managed port; there is not yet a public session registry or command contract. Aetheria will name one Ymir session per run and zone when that contract is exposed. Its old process-wide simulator objects are not session identifiers. Planar heading, angular velocity, and transient torque already pass through Box3D. Typed begin/end/hit lifecycle facts, checkpoint reconstruction, and non-Windows RID artifacts remain cutover work.

See the architecture map and the executable parity contract.

Build And Test

Initialize the pinned dependency and run the solution:

git submodule update --init --recursive
dotnet test Ymir.slnx

The parity project builds the native shim from source and requires CMake plus a C17 compiler:

dotnet test tests\Ymir.Box3D.Parity\Ymir.Box3D.Parity.csproj

Box3D is MIT licensed. Its license is retained in extern/box3d.

GameCult.Ymir.Box3D packages the managed boundary, Box3D license, and native facade under runtimes/<rid>/native. A local Windows x64 package has loaded in an isolated empty consumer without CMake or the submodule. A committed release smoke is still required before that is a repeatable packaging guarantee. Linux and macOS packages must be produced and smoked on their own release workers before those RIDs are advertised.

Cutover Rule

A Ymir cutover is complete only when all runtime stepping, collision queries, and contact facts come from Box3D through an explicitly owned Ymir session. Manual Unity callbacks and Aetheria geometry tests must be structurally unable to decide the result. Snapshot compatibility calls may use isolated sessions; they are not allowed to infer or share retained-world identity.