[Server] Merge the twoAskProtocol() docblocks, note returning to a single key

Author: chr-hertel

docs/handlers/input-required.md

@@ -106,6 +106,9 @@ Pass a list of keys instead of one, and the first key signs while every key veri
 ->setRequestState([$_ENV['MCP_REQUEST_STATE_KEY'], $_ENV['MCP_REQUEST_STATE_KEY_PREVIOUS']], ttl: 600)
 ```
 
+Every entry must be a key: once the rotation is done, go back to a single key instead of
+leaving an unset variable in the list.
+
 A state names no key, so the wire format does not change and a single key is a ring of one.
 To rotate without failing the calls in flight:
 

tests/Unit/Server/Stateless/StatelessProtocolTest.php

@@ -576,8 +576,7 @@ public function testUndeclaredGatewayElicitationIsRefused(): void
     /**
      * A handler asking twice: the second round has to remember the first
      * round's answer, which is what the `requestState` is for.
-     */
-    /**
+     *
      * @param string|list<string>|null $key the signing key or key ring, a fixed test key by default
      */
     private static function twoAskProtocol(bool $signed = true, string|array|null $key = null): StatelessProtocol