SushiEngine architecture

This directory explains how SushiEngine is put together: the relationship to SushiRuntime, the tier layering the modules are arranged into, and the seams a non-trivial change will touch. It is one file per subject, grouped the way cmake/EngineLayers.cmake groups the code — foundation → domain → asset → presentation → world — so the file you need is the tier the change lands in. Read docs/architecture/OVERVIEW.md before anything else; read the rest when a change crosses into them.

File	What it covers
`docs/architecture/OVERVIEW.md`	The head/battery split with SushiRuntime, and the layer table every module sits in.
`docs/architecture/FOUNDATION.md`	The ECS, archetype-chunk storage and the system graph, and the value-type seam all precision rests on.
`docs/architecture/PROFILING.md`	The trace timeline: per-thread zones, device tracks, log markers, the built-in and Tracy backends, and capturing.
`docs/architecture/DOMAIN_PHYSICS.md`	The graph-coloured PGS and XPBD solvers, colliders and contacts, and their editor authoring.
`docs/architecture/DOMAIN_ASTRO.md`	The ephemeris, celestial lighting, gravity field, reference frames, and frame-local authoring.
`docs/architecture/DOMAIN_UI.md`	The retained ECS canvas, its anchor solver and façade, and the render pass that composites it.
`docs/architecture/DOMAIN_ANIMATION.md`	Skeletons, clips and controllers, the deterministic animator tick, blend trees, layers, IK, morphs and retargeting.
`docs/architecture/DOMAIN_INPUT.md`	Device-abstracted actions, bindings as data, the SDL backend, rebinding, touch, and the tick boundary.
`docs/architecture/DOMAIN_AUDIO.md`	The two-plane audio engine: DSP core, mixer and voices, propagation, spatialization, reverb, the ECS bridge, and the bank pipeline.
`docs/architecture/DOMAIN_VFX.md`	The particle authoring model, its deterministic CPU and cosmetic GPU backends, every render alignment, and the particle material.
`docs/architecture/DOMAIN_ATMOSPHERE.md`	Weather providers and the cloudscape they compile to, the spatial weather field and window, and the GPU regional nest.
`docs/architecture/DOMAIN_TERRAIN.md`	The cube-sphere quadtree, the editable layer stack, the height-source and pack formats, and the terrain draw.
`docs/architecture/PRESENTATION_RENDER.md`	The RHI and scene-view seams, and the frame graph the passes register into.
`docs/architecture/PRESENTATION_RENDER_SHADING.md`	What the passes compute: materials and IBL, the temporal core, shadows, and the lighting and sky passes.
`docs/architecture/VOLUMETRIC_CLOUDS.md`	The cloud system as built after the repair program: the single-source planet map, the carve’s semantics, measured tier budgets, the capture probe workflow, and the open backlog.
`docs/architecture/WORLD.md`	SushiLoop’s snapshot/rollback buffer, the loopback network reconciliation, and the `Loop::App` host loop.
`docs/architecture/TOOLING.md`	The functional test suite’s shape and what it pins, and the `se` developer CLI.
`docs/design/ROADMAP.md`	The milestones — what has landed, what is in progress, and the editor and player host shells.