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, 21 insertions, 0 deletions

diff --git a/scripts/plugin-stub-generator/src/SourceFile.php b/scripts/plugin-stub-generator/src/SourceFile.php
index 771e83a8..e20bf00f 100644
--- a/scripts/plugin-stub-generator/src/SourceFile.php
+++ b/scripts/plugin-stub-generator/src/SourceFile.php
@@ -4,6 +4,7 @@ declare(strict_types=1);
 
 namespace Shirabe\PluginStubGenerator;
 
+use PhpParser\Node\Name;
 use PhpParser\Node\Stmt\ClassLike;
 use PhpParser\Node\Stmt\GroupUse;
 use PhpParser\Node\Stmt\Namespace_;
@@ -83,4 +84,24 @@ final class SourceFile
     {
         return implode("\n", array_slice($this->lines, $startLine - 1, $endLine - $startLine + 1));
     }
+
+    /** This file's imports, restricted to the names the emitted text actually uses. */
+    public function importsUsedBy(string $emittedText): string
+    {
+        $kept = [];
+        foreach ($this->aliases as $alias => $fqcn) {
+            if (preg_match('/(?<![\\\\$\w])' . preg_quote($alias, '/') . '\b/', $emittedText) === 1) {
+                $kept[] = 'use ' . $fqcn
+                    . (str_ends_with($fqcn, '\\' . $alias) || $fqcn === $alias ? '' : " as $alias") . ';';
+            }
+        }
+        return implode("\n", $kept);
+    }
+
+    /** The FQCN a Name node resolved to, the NameResolver having left the node itself alone. */
+    public static function resolvedName(Name $name): string
+    {
+        $resolved = $name->getAttribute('resolvedName');
+        return $resolved instanceof Name ? $resolved->toString() : $name->toString();
+    }
 }