API gateway

Product guide: what the capability brings, for whom, its limits and the version that delivered it - no configuration syntax.

What it does	Serves the operations declared in an OpenAPI 3.1 contract and relays them to their upstreams. An undeclared route does not exist; an operation without an upstream stops the start. SSE and WebSocket streams are relayed without holding. The configuration changes without a restart, and an invalid one never replaces the running one
Why it matters	The API's documentation and what the gateway serves can no longer drift. Errors follow one format (RFC 9457) a client can switch on without reading a sentence. Real-time streams arrive as they are produced, where gateways on the market deliver them in one block
Use cases	Expose a public or partner API; replace an existing gateway without regression (1.0.0 proved it on a real product moving off another gateway); serve several APIs on one gateway, each on its host; relay a live dashboard
Resilience	A timeout per operation, retries limited to replayable requests, a circuit breaker per upstream, bulkheads, load shedding when the gateway saturates - and every degradation is announced to the client, never silent
Taking over	The configuration of an existing gateway converts offline, with a report of what is taken over and what is not (1.2.0)
Limits	No aggregation of several upstreams into one response, no HTTP/3 on the caller side, no XML or form decoders (What is not built yet); serves no static files
Since	0.1.0 (contract), 0.2.0 (request path, streams), 0.1.0 (live configuration), 1.0.0 (load shedding, first version that promises compatibility)
Configure	Serving your first API, Take over an existing gateway, 7