supergraph_source_plugin.md

hive-router-config	minor

Add supergraph.source: plugin for deployments where plugins are the only source of supergraphs

This source creates no loader and has no configured fallback. Readiness, GraphQL requests, and WebSocket upgrades return service unavailable until the request's plugin selects a usable supergraph.

HTTP readiness checks invoke plugin's on_http_request, in order for the readiness check to pass - a supergraph must be selected even during that readiness request.

See plugin_examples/feature_flags for supergraph.source: plugin with all variants selected by the plugin.