[Server] Point a refused gateway request at InputRequiredResult

docs/handlers/input-required.md

@@ -116,11 +116,17 @@ They can return `true` there, but `sample()` and `listRoots()` still fail (see b
 ## What not to call
 
 `ClientGateway::sample()` and `listRoots()` belong to the handshake era. Revision
-`2026-07-28` removed both, so calling one there fails the call with an internal error
-(`-32603`). The error happens outside your handler, so a `try`/`catch` around the call
-never runs. Take what they gave you from tool arguments, resource URIs or server
-configuration instead. `elicit()` and `elicitUrl()` are unaffected: elicitation survived
-that revision, as an ask carried in the result.
+`2026-07-28` has no server-initiated requests, so calling one there fails the call with an
+internal error (`-32603`). The error happens outside your handler, so a `try`/`catch` around
+the call never runs. To sample or list roots on that revision,
+[return the ask](#returning-the-ask) as an `InputRequiredResult` with a
+`CreateSamplingMessageRequest` or `ListRootsRequest`, and read the answer with
+`samplingResult()` or `rootsResult()`. `elicit()` and `elicitUrl()` are unaffected: the SDK
+turns them into such an ask for you.
+
+Sampling and roots are deprecated since `2026-07-28`
+([SEP-2577](https://github.com/modelcontextprotocol/modelcontextprotocol/pull/2577)). For new
+code, prefer tool arguments, resource URIs or server configuration.
 
 ## Which revision called
 

src/Server/Stateless/StatelessProtocol.php

@@ -723,9 +723,10 @@ private function readNotification(mixed $suspended, RequestMeta $meta): ?Notific
         if (!$suspended instanceof NotificationSuspension) {
             if ($suspended instanceof RequestSuspension) {
                 // Elicitation never reaches here — it is answered in run(). What
-                // is left are the kinds this revision removed outright, and no
-                // multi round-trip shape brings them back.
-                throw new LogicException('This protocol revision has no server-initiated requests: sampling and roots were removed with it, so take what you need through tool arguments, resource URIs or server configuration instead. Elicitation is the one ask that survived, as a multi round-trip request.');
+                // is left, sampling and roots, cannot be sent from inside a request
+                // on this revision, but a handler still gets them answered by
+                // returning them as an InputRequiredResult.
+                throw new LogicException(\sprintf('This protocol revision has no server-initiated requests, so "%s" cannot be sent from inside a request. Return it from the handler as an InputRequiredResult instead, and read the answer from RequestContext::getInputContext() when the client retries.', $suspended->request::getMethod()));
             }
 
             return null;

tests/Integration/SamplingTest.php

@@ -118,9 +118,10 @@ public function testSamplingIsUnavailableOnTheModernEra(): void
 
         try {
             $client->callTool('summarize', ['text' => 'hello']);
-            $this->fail('Sampling must not be reachable on 2026-07-28, which removed it.');
+            $this->fail('Sampling must not be sent from inside a request on 2026-07-28.');
         } catch (RequestException $e) {
-            $this->assertStringContainsString('sampling and roots were removed', $e->getMessage());
+            $this->assertStringContainsString('"sampling/createMessage"', $e->getMessage());
+            $this->assertStringContainsString('InputRequiredResult', $e->getMessage());
         }
     }
 

tests/Unit/Server/Stateless/StatelessProtocolTest.php

@@ -502,6 +502,8 @@ public function testServerInitiatedRequestIsRefused(): void
 
         $this->assertSame(500, $result->httpStatus);
         $this->assertStringContainsString('no server-initiated requests', $body['error']['message']);
+        $this->assertStringContainsString('"roots/list"', $body['error']['message']);
+        $this->assertStringContainsString('InputRequiredResult', $body['error']['message']);
     }
 
     #[TestDox('a gateway elicitation becomes the ask this revision carries in the result')]