Crate layers#

Core’s crates are organised into four layers.

tw-types · tw-protocol · tw-provider · tw-resil · tw-crypto   ← defined by external constraints
tw-engine · tw-pricing · tw-redact · tw-yaml · tw-secret      ← domain logic
tw-config · tw-store · tw-scan · tw-adopt · tw-observe        ← assembly
tw-gateway · tw-control                                       ← data plane / control plane

Layer	Crates	Role
1	`tw-types`, `tw-protocol`, `tw-provider`, `tw-resil`, `tw-crypto`	Defined by external constraints
2	`tw-engine`, `tw-pricing`, `tw-redact`, `tw-yaml`, `tw-secret`	Domain logic
3	`tw-config`, `tw-store`, `tw-scan`, `tw-adopt`, `tw-observe`	Assembly
4	`tw-gateway`, `tw-control`	Data plane and control plane

Shared layers#

The top two layers remain stable with respect to external constraints. The server edition depends on them directly.

Unshared layers#

The bottom two layers form the single-machine implementation, built on SQLite and a unix socket, and are intentionally not shared. Single-machine SQLite and multi-tenant Postgres differ too much for one abstraction to serve both.

Price list in tw-pricing#

crates/tw-pricing embeds a pinned price snapshot that is not updated automatically. Tracking upstream automatically would allow two builds to compute different prices, and a discrepancy between one day’s figures and the next could not be explained to users. See Development and tests for the snapshot update procedure.