Cast variadic tool parameters element-by-element

src/Capability/Registry/ReferenceHandler.php

@@ -99,10 +99,33 @@ private function prepareArguments(\ReflectionFunctionAbstract $reflection, array
         $finalArgs = [];
 
         foreach ($reflection->getParameters() as $parameter) {
-            // TODO: Handle variadic parameters.
             $paramName = $parameter->getName();
             $paramPosition = $parameter->getPosition();
 
+            if ($parameter->isVariadic()) {
+                // SchemaGenerator advertises variadic parameters as a JSON "array"
+                // schema (see buildVariadicParameterSchema()), so the incoming value
+                // here is an array whose elements each need casting to the variadic's
+                // element type. Falling through to castArgumentType() below would try
+                // to cast the whole array as a single scalar and fail (e.g. "Cannot
+                // cast value to integer" for `int ...$extra`). Variadic is always the
+                // last parameter, so appending here preserves correct final ordering.
+                $values = $arguments[$paramName] ?? [];
+                if (!\is_array($values)) {
+                    throw RegistryException::invalidParams(\sprintf('Parameter `%s` must be an array of values.', $paramName));
+                }
+                foreach (array_values($values) as $value) {
+                    try {
+                        $finalArgs[] = $this->castArgumentType($value, $parameter);
+                    } catch (InvalidArgumentException $e) {
+                        throw RegistryException::invalidParams($e->getMessage(), $e);
+                    } catch (\Throwable $e) {
+                        throw RegistryException::internalError("Error processing parameter `{$paramName}`: {$e->getMessage()}", $e);
+                    }
+                }
+                continue;
+            }
+
             // Check if parameter is a special injectable type
             $type = $parameter->getType();
             if ($type instanceof \ReflectionNamedType && !$type->isBuiltin()) {

tests/Unit/Capability/Registry/ReferenceHandlerTest.php

@@ -14,6 +14,7 @@
 use Mcp\Capability\Registry\ElementReference;
 use Mcp\Capability\Registry\ReferenceHandler;
 use Mcp\Exception\InvalidArgumentException;
+use Mcp\Exception\RegistryException;
 use Mcp\Server\ClientGateway;
 use Mcp\Server\Handler\ResourceHandlerInterface;
 use Mcp\Server\Handler\ToolHandlerInterface;
@@ -141,4 +142,49 @@ public function testHandleThrowsForStringHandlerThatIsNeitherFunctionNorClass():
 
         (new ReferenceHandler())->handle($reference, ['_session' => $session]);
     }
+
+    public function testHandleCastsEachElementOfAnArrayArgumentForAVariadicParameter(): void
+    {
+        // SchemaGenerator advertises variadic parameters as a JSON "array" schema,
+        // so the array arrives here as a single named argument (not spread across
+        // multiple keys) and must be cast element-by-element to the variadic's type.
+        $closure = static fn (string $name, int ...$scores): string => \sprintf('%s:%d', $name, array_sum($scores));
+        $reference = new ElementReference($closure);
+
+        $result = (new ReferenceHandler())->handle($reference, [
+            '_session' => $this->createMock(SessionInterface::class),
+            'name' => 'total',
+            'scores' => ['1', '2', '3'],
+        ]);
+
+        $this->assertSame('total:6', $result);
+    }
+
+    public function testHandleTreatsOmittedVariadicArgumentAsZeroElements(): void
+    {
+        $closure = static fn (string $name, int ...$scores): int => \count($scores);
+        $reference = new ElementReference($closure);
+
+        $result = (new ReferenceHandler())->handle($reference, [
+            '_session' => $this->createMock(SessionInterface::class),
+            'name' => 'empty',
+        ]);
+
+        $this->assertSame(0, $result);
+    }
+
+    public function testHandleThrowsRegistryExceptionWhenVariadicArgumentIsNotAnArray(): void
+    {
+        $closure = static fn (string $name, int ...$scores): int => \count($scores);
+        $reference = new ElementReference($closure);
+
+        $this->expectException(RegistryException::class);
+        $this->expectExceptionMessage('Parameter `scores` must be an array of values.');
+
+        (new ReferenceHandler())->handle($reference, [
+            '_session' => $this->createMock(SessionInterface::class),
+            'name' => 'bad',
+            'scores' => 'not-an-array',
+        ]);
+    }
 }