WebSocket protocol contract

This directory is the single source of truth for the browser/server WebSocket protocol. The JSON Schema files here (draft 2020-12) are the only editable authority: the Python pydantic models under server/schemas/, the generated TypeScript under client/src/protocol/generated.ts, and the wire itself are all derived from or checked against these schemas.

• protocol_version.txt — the current version string. It is the single source of protocol_version for the server, both envelopes, and codegen.
• envelope.schema.json — the shared $defs vocabulary.
• client_message.schema.json — the inbound (browser → server) envelope.
• server_message.schema.json — the outbound (server → browser) envelope.
• payloads/*.schema.json — the nested payload shapes.
• codegen/generate_ts.mjs — emits client/src/protocol/generated.ts.

How to change the contract

Additive is the default; breaking changes are a MAJOR bump. Edit the schema first, then regenerate and let the parity test (tests/test_protocol_schema_parity.py) prove the Python models still agree.

1. Additive, non-breaking (no version bump). Adding an optional payload key, a new descriptive envelope field, or relaxing a constraint is allowed without changing protocol_version. Every envelope and payload sets additionalProperties: true, so consumers MUST ignore unknown fields and MUST NOT rely on field ordering.
2. New type enum value (MINOR bump). Adding a value to a type enum is additive but breaking for a closed consumer, so it requires a MINOR bump (1.0 → 1.1). A consumer that does not recognise a new type MUST ignore the message and continue, never crash.
3. MAJOR bump (1.x → 2.0). Removing or renaming a type, removing or retyping an existing field, changing required-ness, or changing a const is a MAJOR bump. MAJOR bumps require a coordinated server + dashboard release and a shim window.

When the version changes, update protocol_version.txt and the const in both envelopes together; the parity test asserts they stay equal.

Regenerating the TypeScript

cd client
npm install            # once, to pick up json-schema-to-typescript
npm run gen:protocol   # writes client/src/protocol/generated.ts

CI enforces git diff --exit-code client/src/protocol/generated.ts after npm run gen:protocol, so a schema change without regenerated types fails, and a generated-type change without a schema change fails too.

Compatibility policy (summary)

Change	Version action	Consumer rule
New optional field / payload key	none	ignore unknown fields
New type enum value	MINOR	ignore unknown type
Remove / rename / retype / re-required	MAJOR	coordinate a release

Missing protocol_version. An inbound message without protocol_version is rejected with a type: "error" message carrying payload.code = "protocol_version_mismatch", exactly like a present value whose MAJOR component differs from the server's. (Phase 1 accepted a missing version as legacy "0.x" with a one-line deprecation log; that transition window is closed as of Phase 2.)