Architecture

Foundry ships as a set of Unity packages, each with its own manifest, its own assembly definitions, and its own tests. A package declares what it depends on, and the architecture tests fail the build when an assembly reaches past that declaration. Every other property described here follows from that one rule.

Adoption is therefore incremental. You can take Inventory without Equipment, Armory without a player controller, and Persistence without Networking. A lower layer holds no reference to the layers above it, so a system you skip is absent from the build instead of sitting dormant in it.

Two packages sit underneath everything and depend on nothing at all. Messaging carries events and resolves services. Foundation carries the primitives, the definition registry, and the diagnostics gate. Two packages that need to talk without knowing about each other go through one of those two.

Something happened: publish it on the event bus. A weapon that finishes reloading does not know the HUD exists, and the HUD does not know which weapon fired the event. Both know the message type, which lives in whichever package owns the concept.

Something is needed: resolve it from the service registry. A HUD component that needs theme data resolves IHudTheme rather than importing Equipment, which is why UI Theming is contract-only and depends on nothing.

Something must be authored: define it as a ScriptableObject. Definitions are the seam between designers and code across the whole stack, and the definition registry in Foundation is how a runtime system finds one without holding a hard reference to it.