protobuf-architectlisted

# Protocol Buffers Architecture Language-agnostic schema standards. Proto files target **proto3** + `buf` toolchain. Validation uses `protovalidate` (CEL). Code generation is per-language and out of scope here — see the language architect skill for the generated-code idioms (e.g. [go-architect](../../languages/go-architect/SKILL.md) when generating for Go). File-layout, validation, codegen, and breaking-check snippets in [RECIPES.md](RECIPES.md); pinned tool versions in [STACK.md](STACK.md). ## 1. File layout & package naming Buf-style hierarchical packages — `<org>.<product>.<resource>.<version>`. Mirrors the on-disk path. One service or coherent message group per file. Tree + package declaration in [RECIPES.md](RECIPES.md). - **Package = directory path.** `acme/shop/users/v1/` → `package acme.shop.users.v1;`. Enforced by `buf lint`. - **Per-language `option *_package`** declarations live in every file. Set them up-front; don't refactor later (it's a breaking change). - **One `service`** definition per file; supporting messages can live alongside or in sibling files. ## 2. Message design - **All fields are `optional` semantically in proto3.** Use the explicit `optional` keyword (proto3.15+) when "field absent" must be distinguishable from "field present with zero value" — common for PATCH-style partial updates. - **Field names: `snake_case`.** Enforced by `buf lint`. The language plugin converts to the target idiom (Go `CamelCase`, Python `snake_case`, etc.). - **Messa