[Client] Speak the 2026-07-28 lifecycle (#456)

* [Client] Speak the 2026-07-28 lifecycle

On that revision the client opens with server/discover instead of
initialize, stamps each request's _meta with the protocol version, its own
capabilities and client info, and sends the standard Mcp-Method / Mcp-Name /
Mcp-Param-* headers an intermediary routes on. ToolCatalog is what knows,
from the tool list, which arguments a call has to mirror.

An input_required result is answered rather than surfaced: InputRequestResolver
asks the host's elicitation, sampling and roots handlers and retries the same
request carrying inputResponses and the requestState the server sent.

McpHeader holds the header names and the =?base64?…?= sentinel, so the two
sides no longer keep their own copies of the same rules.

* Fix CI baseline drift and address Copilot review findings

Drop stale expected-failure entries the new client fixture now passes.

Copilot review: fix McpHeader round-trip for a wrapper-shaped literal,
encode empty/numeric-keyed inputResponses as a JSON object, stop the
incident example repeating side effects on MRTR retry, and reset
ToolCatalog on reconnect instead of carrying the previous server's
verdicts.

* Skip DualEraExampleTestCase on PHP 8.1

PHP_CLI_SERVER_WORKERS does not reliably fork multiple php -S
workers there (php/php-src#9400), reproducing the single-worker
deadlock the extra workers exist to avoid.

tests/Unit/Schema/Wire/McpHeaderTest.php

@@ -0,0 +1,93 @@
+<?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\Unit\Schema\Wire;
+
+use Mcp\Schema\Wire\McpHeader;
+use PHPUnit\Framework\Attributes\DataProvider;
+use PHPUnit\Framework\Attributes\TestDox;
+use PHPUnit\Framework\TestCase;
+
+/**
+ * The encoding rules both sides of the wire depend on (SEP-2243).
+ *
+ * The round-trip property is what actually matters: whatever the client wraps,
+ * the server's reader must recover unchanged. A rule that only one side gets
+ * right produces a header mismatch the caller cannot explain.
+ */
+final class McpHeaderTest extends TestCase
+{
+    /**
+     * @return iterable<string, array{mixed, string}>
+     */
+    public static function provideValues(): iterable
+    {
+        yield 'plain ascii' => ['us-west1', 'us-west1'];
+        yield 'empty string' => ['', ''];
+        yield 'interior spaces stay plain' => ['us west 1', 'us west 1'];
+        yield 'integer' => [42, '42'];
+        yield 'boolean true' => [true, 'true'];
+        yield 'boolean false' => [false, 'false'];
+        yield 'non-ascii is wrapped' => ['Hello, 世界', '=?base64?SGVsbG8sIOS4lueVjA==?='];
+        yield 'leading space is wrapped' => [' us-west1', '=?base64?IHVzLXdlc3Qx?='];
+        yield 'trailing space is wrapped' => ['us-west1 ', '=?base64?dXMtd2VzdDEg?='];
+        yield 'newline is wrapped' => ["line1\nline2", '=?base64?bGluZTEKbGluZTI=?='];
+        yield 'tab is wrapped' => ["\tindented", '=?base64?CWluZGVudGVk?='];
+        yield 'a literal already shaped like the wrapper is wrapped again' => ['=?base64?SGVsbG8=?=', '=?base64?PT9iYXNlNjQ/U0dWc2JHOD0/PQ==?='];
+    }
+
+    #[DataProvider('provideValues')]
+    #[TestDox('renders a mirrored argument as a header value')]
+    public function testEncode(mixed $value, string $expected): void
+    {
+        $this->assertSame($expected, McpHeader::encode($value));
+    }
+
+    #[DataProvider('provideValues')]
+    #[TestDox('what the client wraps, the server recovers unchanged')]
+    public function testRoundTrip(mixed $value, string $encoded): void
+    {
+        $expected = match (true) {
+            \is_bool($value) => $value ? 'true' : 'false',
+            default => (string) $value,
+        };
+
+        $this->assertSame($expected, McpHeader::decode($encoded));
+    }
+
+    #[TestDox('a value that cannot be mirrored gets no header at all')]
+    public function testUnmirrorableValue(): void
+    {
+        // A float has no single decimal spelling for a receiver to compare
+        // against, which is why SEP-2243 forbids the annotation on `number`.
+        $this->assertNull(McpHeader::encode(3.14159));
+        $this->assertNull(McpHeader::encode(['a']));
+        $this->assertNull(McpHeader::encode(null));
+    }
+
+    #[TestDox('a corrupted wrapper is refused rather than silently decoded')]
+    public function testCorruptWrapperIsRefused(): void
+    {
+        $this->assertNull(McpHeader::decode('=?base64?not valid base64!?='));
+    }
+
+    #[TestDox('names the subject of the methods that address one, and nothing else')]
+    public function testNameFor(): void
+    {
+        $this->assertSame('my-tool', McpHeader::nameFor('tools/call', ['name' => 'my-tool']));
+        $this->assertSame('my-prompt', McpHeader::nameFor('prompts/get', ['name' => 'my-prompt']));
+        $this->assertSame('file:///x', McpHeader::nameFor('resources/read', ['uri' => 'file:///x']));
+        $this->assertSame('t-1', McpHeader::nameFor('tasks/get', ['taskId' => 't-1']));
+
+        $this->assertNull(McpHeader::nameFor('tools/list', []));
+        $this->assertNull(McpHeader::nameFor('tools/call', null));
+    }
+}