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, 30 insertions, 3 deletions

diff --git a/scripts/plugin-stub-generator/src/Report.php b/scripts/plugin-stub-generator/src/Report.php
index 92e0565e..758a1768 100644
--- a/scripts/plugin-stub-generator/src/Report.php
+++ b/scripts/plugin-stub-generator/src/Report.php
@@ -7,8 +7,11 @@ namespace Shirabe\PluginStubGenerator;
 /** The classifier report (scripts/plugin-class-classifier/report.json). */
 final class Report
 {
-    /** @param array<string, string> $categories fqcn => category */
-    private function __construct(private readonly array $categories)
+    /**
+     * @param array<string, string> $categories fqcn => category
+     * @param array<string, string> $kinds      fqcn => class / interface / trait / enum
+     */
+    private function __construct(private readonly array $categories, private readonly array $kinds)
     {
     }
 
@@ -24,14 +27,38 @@ final class Report
             throw new GenerationError(["$path records classification violations; fix the classifier lists first"]);
         }
         $categories = [];
+        $kinds = [];
         foreach ($data['classes'] as $class) {
             $categories[$class['fqcn']] = $class['category'];
+            $kinds[$class['fqcn']] = $class['kind'];
         }
-        return new self($categories);
+        return new self($categories, $kinds);
     }
 
     public function category(string $fqcn): ?string
     {
         return $this->categories[$fqcn] ?? null;
     }
+
+    public function kind(string $fqcn): ?string
+    {
+        return $this->kinds[$fqcn] ?? null;
+    }
+
+    /**
+     * The FQCNs of the given categories, in report order.
+     *
+     * @param  list<string> $categories
+     * @return list<string>
+     */
+    public function inCategories(array $categories): array
+    {
+        $out = [];
+        foreach ($this->categories as $fqcn => $category) {
+            if (in_array($category, $categories, true)) {
+                $out[] = $fqcn;
+            }
+        }
+        return $out;
+    }
 }