feat(plugin): guard Rust-owned classes the worker has no proxy for

The worker's autoloader fell through to the real Composer source for every
Rust-owned FQCN without a proxy stub, so plugin code doing `new Filesystem()`
or subclassing `LibraryInstaller` silently ran on a second instance the Rust
side never sees. An unimplemented part of the plugin API has to fail with an
explicit error naming it, not quietly work on a disconnected copy.

The stub generator now emits a guard class for each of those FQCNs: the real
declaration, hierarchy and constants, with every constructor and method
raising an explicit error. References satisfied by the declaration alone
(`instanceof`, `X::class`, `Link::TYPE_REQUIRE`) keep working. Two FQCNs stay
resolvable to the real class, each listed with the worker-side mechanism that
makes a natively constructed instance correct.

The error had nowhere to go: `Installer::run` dropped the `Result` of both
`dispatch_script` calls, so an exception from a listener ended in exit 0.
Both propagate now, the way the exception does upstream.

Three real-plugin E2E comparisons stop at a guard and are ignored, each
naming the class it needs.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

3 files changed, 116 insertions, 0 deletions

diff --git a/crates/shirabe-php-rpc/php/guards/Composer/Util/Http/CurlDownloader.php b/crates/shirabe-php-rpc/php/guards/Composer/Util/Http/CurlDownloader.php
new file mode 100644
index 00000000..5e362356
--- /dev/null
+++ b/crates/shirabe-php-rpc/php/guards/Composer/Util/Http/CurlDownloader.php
@@ -0,0 +1,37 @@
+<?php
+
+// Generated by scripts/plugin-stub-generator; do not edit by hand.
+// Guard for Composer\Util\Http\CurlDownloader.
+// The Rust side owns this class and the worker has no proxy for it, so this
+// declaration shadows the real one: the constants and the hierarchy stay, while
+// constructing it or calling anything on it raises an explicit error.
+
+namespace Composer\Util\Http;
+
+use Composer\Config;
+use Composer\IO\IOInterface;
+
+class CurlDownloader
+{
+    private const BAD_MULTIPLEXING_CURL_VERSIONS = ['7.87.0', '7.88.0', '7.88.1'];
+
+    public function __construct(IOInterface $io, Config $config, array $options = [], bool $disableTls = false)
+    {
+        \ShirabeUnsupportedClass::fail(self::class, '__construct');
+    }
+
+    public function download(callable $resolve, callable $reject, string $origin, string $url, array $options, ?string $copyTo = null): int
+    {
+        \ShirabeUnsupportedClass::fail(self::class, 'download');
+    }
+
+    public function abortRequest(int $id): void
+    {
+        \ShirabeUnsupportedClass::fail(self::class, 'abortRequest');
+    }
+
+    public function tick(): void
+    {
+        \ShirabeUnsupportedClass::fail(self::class, 'tick');
+    }
+}
diff --git a/crates/shirabe-php-rpc/php/guards/Composer/Util/Http/CurlResponse.php b/crates/shirabe-php-rpc/php/guards/Composer/Util/Http/CurlResponse.php
new file mode 100644
index 00000000..ae229589
--- /dev/null
+++ b/crates/shirabe-php-rpc/php/guards/Composer/Util/Http/CurlResponse.php
@@ -0,0 +1,22 @@
+<?php
+
+// Generated by scripts/plugin-stub-generator; do not edit by hand.
+// Guard for Composer\Util\Http\CurlResponse.
+// The Rust side owns this class and the worker has no proxy for it, so this
+// declaration shadows the real one: the constants and the hierarchy stay, while
+// constructing it or calling anything on it raises an explicit error.
+
+namespace Composer\Util\Http;
+
+class CurlResponse extends Response
+{
+    public function __construct(array $request, ?int $code, array $headers, ?string $body, array $curlInfo)
+    {
+        \ShirabeUnsupportedClass::fail(self::class, '__construct');
+    }
+
+    public function getCurlInfo(): array
+    {
+        \ShirabeUnsupportedClass::fail(self::class, 'getCurlInfo');
+    }
+}
diff --git a/crates/shirabe-php-rpc/php/guards/Composer/Util/Http/Response.php b/crates/shirabe-php-rpc/php/guards/Composer/Util/Http/Response.php
new file mode 100644
index 00000000..61eebb7f
--- /dev/null
+++ b/crates/shirabe-php-rpc/php/guards/Composer/Util/Http/Response.php
@@ -0,0 +1,57 @@
+<?php
+
+// Generated by scripts/plugin-stub-generator; do not edit by hand.
+// Guard for Composer\Util\Http\Response.
+// The Rust side owns this class and the worker has no proxy for it, so this
+// declaration shadows the real one: the constants and the hierarchy stay, while
+// constructing it or calling anything on it raises an explicit error.
+
+namespace Composer\Util\Http;
+
+class Response
+{
+    public function __construct(array $request, ?int $code, array $headers, ?string $body)
+    {
+        \ShirabeUnsupportedClass::fail(self::class, '__construct');
+    }
+
+    public function getStatusCode(): int
+    {
+        \ShirabeUnsupportedClass::fail(self::class, 'getStatusCode');
+    }
+
+    public function getStatusMessage(): ?string
+    {
+        \ShirabeUnsupportedClass::fail(self::class, 'getStatusMessage');
+    }
+
+    public function getHeaders(): array
+    {
+        \ShirabeUnsupportedClass::fail(self::class, 'getHeaders');
+    }
+
+    public function getHeader(string $name): ?string
+    {
+        \ShirabeUnsupportedClass::fail(self::class, 'getHeader');
+    }
+
+    public function getBody(): ?string
+    {
+        \ShirabeUnsupportedClass::fail(self::class, 'getBody');
+    }
+
+    public function decodeJson()
+    {
+        \ShirabeUnsupportedClass::fail(self::class, 'decodeJson');
+    }
+
+    public function collect(): void
+    {
+        \ShirabeUnsupportedClass::fail(self::class, 'collect');
+    }
+
+    public static function findHeaderValue(array $headers, string $name): ?string
+    {
+        \ShirabeUnsupportedClass::fail(self::class, 'findHeaderValue');
+    }
+}