[Server] Fix CI: switch warning-log tests to PHPUnit mocks; baseline new conformance scenario

- StreamableHttpTransportTest: replace the anonymous AbstractLogger
  fixture with `$this->createMock(LoggerInterface::class)` so the
  test does not declare a `log()` signature at all. That sidesteps
  both the psr/log v1 LSP incompatibility (untyped parameter) and
  the phpstan `missingType.parameter` complaint in one move, and
  matches how the rest of the suite (CallToolHandlerTest etc.)
  fakes loggers.
- conformance-baseline.yml: mark `server-sse-multiple-streams` as
  an expected failure. The new 2025-11-25 conformance scenario
  exercises `GET → SSE` for parallel server→client streams, which
  the SDK does not implement yet (tracked as #291); the test
  becoming visible is a conformance-suite version bump rather
  than a regression from this PR.

Author: sveneld

tests/Conformance/conformance-baseline.yml

@@ -1,4 +1,5 @@
-server: []
+server:
+  - server-sse-multiple-streams
 
 client:
   - elicitation-sep1034-client-defaults

tests/Unit/Server/Transport/StreamableHttpTransportTest.php

@@ -24,7 +24,7 @@
 use Psr\Http\Message\ServerRequestInterface;
 use Psr\Http\Server\MiddlewareInterface;
 use Psr\Http\Server\RequestHandlerInterface;
-use Psr\Log\AbstractLogger;
+use Psr\Log\LoggerInterface;
 
 final class StreamableHttpTransportTest extends TestCase
 {
@@ -93,7 +93,10 @@ public function testEmptyMiddlewareListDisablesDefaultsAndWarns(): void
             ->withHeader('Host', 'evil.example.com')
             ->withHeader('Origin', 'http://evil.example.com');
 
-        $logger = $this->collectingLogger();
+        $logger = $this->createMock(LoggerInterface::class);
+        $logger->expects($this->once())
+            ->method('warning')
+            ->with($this->stringContains('empty middleware list'));
 
         $transport = new StreamableHttpTransport(
             $request,
@@ -109,11 +112,6 @@ public function testEmptyMiddlewareListDisablesDefaultsAndWarns(): void
         $this->assertNotSame(403, $response->getStatusCode());
         $this->assertFalse($response->hasHeader('Access-Control-Allow-Origin'));
         $this->assertFalse($response->hasHeader('Access-Control-Allow-Methods'));
-
-        // Warning was emitted so an operator can spot the bypass in logs.
-        $warnings = array_filter($logger->records, static fn (array $r): bool => 'warning' === $r['level']);
-        $this->assertNotEmpty($warnings, 'Expected a warning log for the bypassed defaults.');
-        $this->assertStringContainsString('empty middleware list', reset($warnings)['message']);
     }
 
     #[TestDox('null middleware does not trigger the empty-list warning')]
@@ -123,13 +121,11 @@ public function testNullMiddlewareDoesNotWarn(): void
             ->createServerRequest('OPTIONS', 'http://localhost/')
             ->withHeader('Host', 'localhost');
 
-        $logger = $this->collectingLogger();
+        $logger = $this->createMock(LoggerInterface::class);
+        $logger->expects($this->never())->method('warning');
 
         $transport = new StreamableHttpTransport($request, $this->factory, $this->factory, $logger);
         $transport->listen();
-
-        $warnings = array_filter($logger->records, static fn (array $r): bool => 'warning' === $r['level']);
-        $this->assertEmpty($warnings);
     }
 
     #[TestDox('custom middleware composes with default stack via spread')]
@@ -278,17 +274,4 @@ public function process(ServerRequestInterface $request, RequestHandlerInterface
             }
         };
     }
-
-    private function collectingLogger(): object
-    {
-        return new class extends AbstractLogger {
-            /** @var list<array{level: string, message: string}> */
-            public array $records = [];
-
-            public function log($level, \Stringable|string $message, array $context = []): void
-            {
-                $this->records[] = ['level' => (string) $level, 'message' => (string) $message];
-            }
-        };
-    }
 }