[Client] Mark the client disconnected when the stdio server exits

CHANGELOG.md

@@ -57,6 +57,7 @@ All notable changes to `mcp/sdk` will be documented in this file.
 * Fix `ClientLogger` dropping messages below `warning` on `2026-07-28` requests that ask for a lower level with `io.modelcontextprotocol/logLevel`.
 * Resume an interrupted SSE response in `HttpTransport` with a GET carrying `Last-Event-ID`, honouring the server's `retry` interval. Configure attempts and fallback backoff with `ReconnectPolicy`, the scheduling clock with any PSR-20 `ClockInterface` (default: a monotonic clock). Protocol version `2026-07-28` does not resume streams. A stream that ends without its response and without an event ID now fails the request instead of waiting for its timeout.
 * Fix a client `onProgress` callback receiving progress for an earlier request that timed out: progress now only reaches the callback of the request whose `progressToken` it carries.
+* Fix `Client::isConnected()` staying true after the stdio server process exited, which left later calls failing against the dead process.
 
 0.8.1
 -----

src/Client/Transport/StdioTransport.php

@@ -142,6 +142,8 @@ public function send(string $data): void
         }
 
         if (false === @fwrite($this->stdin, $data."\n")) {
+            $this->state?->setInitialized(false);
+
             throw new ConnectionException('Could not write to the server process; it is no longer running.');
         }
 
@@ -276,6 +278,8 @@ private function processInput(): void
 
         // Only on an empty read, so an answer arriving with the end of output is taken first.
         if (('' === $data || false === $data) && \is_resource($this->stdout) && feof($this->stdout)) {
+            // The client has to connect again before its next call.
+            $this->state?->setInitialized(false);
             $this->failPending($this->exitReason(), [self::CONNECTION_LOST => true]);
         }
     }

tests/Integration/DeadServerTest.php

@@ -0,0 +1,41 @@
+<?php
+
+/*
+ * This file is part of the official PHP MCP SDK.
+ *
+ * A collaboration between Symfony and the PHP Foundation.
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace Mcp\Tests\Integration;
+
+use Mcp\Exception\ConnectionException;
+use Mcp\Exception\ExceptionInterface;
+use Mcp\Schema\Enum\ProtocolVersion;
+use PHPUnit\Framework\Attributes\DataProvider;
+use PHPUnit\Framework\Attributes\TestDox;
+
+final class DeadServerTest extends IntegrationTestCase
+{
+    #[DataProvider('provideEras')]
+    #[TestDox('a server exiting mid-call leaves the client disconnected on $_dataName')]
+    public function testExitedServerDisconnectsTheClient(ProtocolVersion $version): void
+    {
+        $client = $this->connect('dead_server', $this->clientBuilder()->setProtocolVersion($version));
+
+        try {
+            $client->callTool('exit');
+            $this->fail('A call the server dies in must fail.');
+        } catch (ExceptionInterface) {
+        }
+
+        $this->assertFalse($client->isConnected());
+
+        $this->expectException(ConnectionException::class);
+        $this->expectExceptionMessage('Client is not connected.');
+
+        $client->callTool('fast');
+    }
+}

tests/Integration/Fixture/dead_server.php

@@ -0,0 +1,36 @@
+<?php
+
+/*
+ * This file is part of the official PHP MCP SDK.
+ *
+ * A collaboration between Symfony and the PHP Foundation.
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+/*
+ * Server for {@see \Mcp\Tests\Integration\DeadServerTest}.
+ */
+
+use Mcp\Server;
+use Mcp\Server\Transport\StdioTransport;
+
+require_once dirname(__DIR__, 3).'/vendor/autoload.php';
+
+Server::builder()
+    ->setServerInfo('integration-server', '1.0.0')
+    ->addTool(
+        static function (): string {
+            exit(1);
+        },
+        name: 'exit',
+        description: 'Ends the server process without answering.',
+    )
+    ->addTool(
+        static fn (): string => 'quick',
+        name: 'fast',
+        description: 'Returns at once.',
+    )
+    ->build()
+    ->run(new StdioTransport());

tests/Unit/Client/Transport/StdioTransportTest.php

@@ -86,6 +86,7 @@ public function testClosedOutputFailsPendingRequests(): void
     {
         $transport = new StdioTransport(command: 'true');
         $state = new ClientState();
+        $state->setInitialized(true);
         $transport->setState($state);
         $state->addPendingRequest(1, 120);
 
@@ -97,6 +98,28 @@ public function testClosedOutputFailsPendingRequests(): void
         $this->assertInstanceOf(Error::class, $response);
         $this->assertSame('The server process closed its output.', $response->message);
         $this->assertSame([TransportInterface::CONNECTION_LOST => true], $response->data);
+        $this->assertFalse($state->isInitialized());
+    }
+
+    #[TestDox('a server that can no longer be written to leaves the client uninitialized')]
+    public function testFailedWriteUninitializesTheClient(): void
+    {
+        $transport = new StdioTransport(command: 'true');
+        $state = new ClientState();
+        $state->setInitialized(true);
+        $transport->setState($state);
+
+        $stdin = fopen('php://temp', 'r');
+        $this->assertNotFalse($stdin);
+        (new \ReflectionProperty($transport, 'stdin'))->setValue($transport, $stdin);
+
+        try {
+            $transport->send('{"jsonrpc":"2.0","id":1,"method":"ping"}');
+            $this->fail('Writing to a server that is gone must fail.');
+        } catch (ConnectionException) {
+        }
+
+        $this->assertFalse($state->isInitialized());
     }
 
     /**