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>

1 files changed, 40 insertions, 0 deletions

diff --git a/crates/shirabe-php-rpc/php/guards/Composer/Util/GitLab.php b/crates/shirabe-php-rpc/php/guards/Composer/Util/GitLab.php
new file mode 100644
index 00000000..4c131f61
--- /dev/null
+++ b/crates/shirabe-php-rpc/php/guards/Composer/Util/GitLab.php
@@ -0,0 +1,40 @@
+<?php
+
+// Generated by scripts/plugin-stub-generator; do not edit by hand.
+// Guard for Composer\Util\GitLab.
+// 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;
+
+use Composer\IO\IOInterface;
+use Composer\Config;
+
+class GitLab
+{
+    public function __construct(IOInterface $io, Config $config, ?ProcessExecutor $process = null, ?HttpDownloader $httpDownloader = null)
+    {
+        \ShirabeUnsupportedClass::fail(self::class, '__construct');
+    }
+
+    public function authorizeOAuth(string $originUrl): bool
+    {
+        \ShirabeUnsupportedClass::fail(self::class, 'authorizeOAuth');
+    }
+
+    public function authorizeOAuthInteractively(string $scheme, string $originUrl, ?string $message = null): bool
+    {
+        \ShirabeUnsupportedClass::fail(self::class, 'authorizeOAuthInteractively');
+    }
+
+    public function authorizeOAuthRefresh(string $scheme, string $originUrl): bool
+    {
+        \ShirabeUnsupportedClass::fail(self::class, 'authorizeOAuthRefresh');
+    }
+
+    public function isOAuthExpired(string $originUrl): bool
+    {
+        \ShirabeUnsupportedClass::fail(self::class, 'isOAuthExpired');
+    }
+}