We use TypeBox schemas in `src/gateway/protocol/schema.ts` as the single source of truth for the Gateway control plane (connect/req/res/event frames and payloads). All derived artifacts should be generated from these schemas, not edited by hand.
- Custom `init(from:)` / `encode(to:)` enforces the `type` discriminator and can include an `unknown` case for forward compatibility.
- Wire a new script (e.g., `pnpm protocol:gen:swift`) into `protocol:check` so CI fails if the generated Swift is stale.
Why this path:
- Single source of truth stays TypeBox; no new IDL to maintain.
- Predictable, strongly typed Swift (no optional soup).
- Small deterministic codegen (~150–200 LOC script) we control.
## Alternative (if we want off-the-shelf codegen)
- Wrap the existing JSON Schema into an OpenAPI 3.1 doc (auto-generated) and use **swift-openapi-generator** or **openapi-generator swift5**. More moving parts, but also yields enums with discriminator support. Keep this as a fallback if we don’t want a custom emitter.
## Action items
- Implement `protocol:gen:swift` that reads the TypeBox schemas and emits the sealed Swift enum + payload structs.
- Update `protocol:check` to include the Swift generator output in the diff check.
- Remove quicktype output once the custom generator is in place (or keep it for docs only).