feat(nano): federating hasJoined multiplexer with per-source UUID namespacing

docs/openapi.yaml

@@ -439,6 +439,41 @@ paths:
         '503':
           $ref: '#/components/responses/ServiceUnavailable'
 
+  /session/minecraft/hasJoined:
+    get:
+      tags: [nano]
+      operationId: hasJoined
+      summary: Multi-source session verifier (Felis-nano hasJoined multiplexer).
+      description: >-
+        Velocity's authlib is pointed here via -Dmojang.sessionserver or a thin login
+        hook. Unauthenticated — the vanilla sessionserver protocol carries no token. The
+        query is fanned out to the configured Yggdrasil roots in priority order (the
+        Mojang identity source first); the first source to validate the serverId hash
+        wins. A non-identity source's self-asserted UUID is rewritten into a per-source
+        namespace (UUIDv3) before return, so it can never land in Mojang's UUID space.
+        A rejected or barred login is 204, which authlib maps to a verify failure.
+      x-felis-face: [internal]
+      x-felis-tier: public
+      security: []
+      parameters:
+        - { name: username, in: query, required: true, schema: { type: string } }
+        - { name: serverId, in: query, required: true, schema: { type: string } }
+        - { name: ip, in: query, required: false, schema: { type: string } }
+      responses:
+        '200':
+          description: A source validated the session; the canonical game profile.
+          content:
+            application/json:
+              schema:
+                type: object
+                required: [id, name]
+                properties:
+                  id: { type: string, description: Canonical UUID, undashed 32-hex. }
+                  name: { type: string }
+                  properties: { type: array, items: { type: object } }
+        '204':
+          description: No source validated the session, or the resolved UUID is barred.
+
   # -------------------------------------------------- internal: servers ------
   /api/v1/servers:
     get: