diff --git a/CHANGELOG.md b/CHANGELOG.md
index 7041d07e..eb1ea471 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -9,6 +9,8 @@ All notable changes to `mcp/sdk` will be documented in this file.
 * [BC Break] `SchemaValidator::validateAgainstJsonSchema()` no longer validates an empty array as an object. Pass `new \stdClass()` for an empty object.
 * Add `Builder::setSchemaValidator()` to configure the validator used for `tools/call` input and output, e.g. with a resolver for external `$ref` schemas.
 * [BC Break] Remove the `providerClass` argument of `#[CompletionProvider]`. Use `provider:`, which takes the same class-string and is now the first positional argument.
+* [BC Break] `StreamableHttpTransport::handleFiberTermination()` takes the terminated `\Fiber` as its first argument; a subclass overriding it has to accept it too.
+* [BC Break] Reject a `Tool` input schema whose `properties` is not an object or whose `required` is neither a list nor `null`, instead of silently replacing the member. Reject a `completion/complete` whose `argument` is missing `name` or `value`, instead of completing against an empty prefix.
 * Add `HttpTransport::getSessionId()` to read the server-minted `Mcp-Session-Id`: a request-scoped caller can persist it and pass it back through the constructor's `$headers` on a later transport. Always `null` on `2026-07-28`, which removed protocol-level sessions.
 * Fix OIDC discovery rejecting issuers with a trailing slash (e.g. Authentik, Auth0).
 * Fix stateless SSE streams holding back frames until close when PHP output buffering is enabled.
diff --git a/examples/client/stdio_elicitation.php b/examples/client/stdio_elicitation.php
index b3dee306..9e6c3834 100644
--- a/examples/client/stdio_elicitation.php
+++ b/examples/client/stdio_elicitation.php
@@ -43,10 +43,14 @@ public function __invoke(ElicitRequest $request): ElicitResult
     {
         echo "\n[ELICIT] {$request->message}\n";
 
+        if (null === $request->requestedSchema) {
+            return new ElicitResult(ElicitAction::Decline);
+        }
+
         $content = [];
         foreach ($request->requestedSchema->properties as $name => $definition) {
             $default = $this->defaultFor($definition);
-            $label = $this->labelFor($definition);
+            $label = $this->labelFor($definition, $name);
 
             if (null !== $default) {
                 $display = is_bool($default) ? ($default ? 'true' : 'false') : (string) $default;
@@ -76,9 +80,11 @@ private function defaultFor(object $definition): mixed
         };
     }
 
-    private function labelFor(AbstractSchemaDefinition $definition): string
+    private function labelFor(AbstractSchemaDefinition $definition, string $name): string
     {
-        return $definition->title;
+        // A schema is not obliged to carry a title, and the field's own name is
+        // a far better prompt than a blank one.
+        return $definition->title ?? $name;
     }
 
     private function cast(object $definition, string $input): mixed
diff --git a/examples/server/bootstrap.php b/examples/server/bootstrap.php
index 99fcfdaf..4b53e610 100644
--- a/examples/server/bootstrap.php
+++ b/examples/server/bootstrap.php
@@ -51,7 +51,7 @@ function transport(): TransportInterface
 
 function shutdown(ResponseInterface|int $result): never
 {
-    if ('cli' === \PHP_SAPI) {
+    if (is_int($result)) {
         exit($result);
     }
 
diff --git a/examples/server/mcp-apps/WeatherApp.php b/examples/server/mcp-apps/WeatherApp.php
index 159e8c47..8269573e 100644
--- a/examples/server/mcp-apps/WeatherApp.php
+++ b/examples/server/mcp-apps/WeatherApp.php
@@ -32,10 +32,15 @@ public function getWeatherApp(): TextResourceContents
             prefersBorder: true,
         );
 
+        $html = file_get_contents(__DIR__.'/weather-app.html');
+        if (false === $html) {
+            throw new \RuntimeException('Could not read the weather app template.');
+        }
+
         return new TextResourceContents(
             uri: 'ui://weather-app',
             mimeType: McpApps::MIME_TYPE,
-            text: file_get_contents(__DIR__.'/weather-app.html'),
+            text: $html,
             meta: ['ui' => $contentMeta],
         );
     }
diff --git a/examples/server/oauth-microsoft/McpElements.php b/examples/server/oauth-microsoft/McpElements.php
index d47a0e52..602797a3 100644
--- a/examples/server/oauth-microsoft/McpElements.php
+++ b/examples/server/oauth-microsoft/McpElements.php
@@ -103,7 +103,7 @@ public function listEmails(int $count = 5): array
                 'id' => 'msg_'.uniqid(),
                 'subject' => "Sample Email #{$i}",
                 'from' => "sender{$i}@example.com",
-                'receivedDateTime' => date('c', strtotime("-{$i} hours")),
+                'receivedDateTime' => date('c', strtotime("-{$i} hours") ?: time()),
             ], range(1, $count)),
         ];
     }
diff --git a/phpstan.dist.neon b/phpstan.dist.neon
index 259c4686..0ff24719 100644
--- a/phpstan.dist.neon
+++ b/phpstan.dist.neon
@@ -2,7 +2,7 @@ includes:
     - phpstan-baseline.neon
 
 parameters:
-    level: 6
+    level: 8
     paths:
         - examples/
         - src/
diff --git a/src/Capability/Attribute/Schema.php b/src/Capability/Attribute/Schema.php
index 80ec4b53..8a375e15 100644
--- a/src/Capability/Attribute/Schema.php
+++ b/src/Capability/Attribute/Schema.php
@@ -29,10 +29,10 @@
  *     minLength?: int,
  *     maxLength?: int,
  *     pattern?: string,
- *     minimum?: int,
- *     maximum?: int,
- *     exclusiveMinimum?: int,
- *     exclusiveMaximum?: int,
+ *     minimum?: int|float,
+ *     maximum?: int|float,
+ *     exclusiveMinimum?: bool,
+ *     exclusiveMaximum?: bool,
  *     multipleOf?: int|float,
  *     items?: array<string, mixed>,
  *     minItems?: int,
diff --git a/src/Capability/Completion/ListCompletionProvider.php b/src/Capability/Completion/ListCompletionProvider.php
index 5d48f4bd..45a41c45 100644
--- a/src/Capability/Completion/ListCompletionProvider.php
+++ b/src/Capability/Completion/ListCompletionProvider.php
@@ -17,11 +17,16 @@
 class ListCompletionProvider implements ProviderInterface
 {
     /**
-     * @param string[] $values
+     * @var string[]
      */
-    public function __construct(
-        private array $values,
-    ) {
+    private array $values;
+
+    /**
+     * @param array<int|float|string> $values
+     */
+    public function __construct(array $values)
+    {
+        $this->values = array_values(array_map(strval(...), $values));
     }
 
     public function getCompletions(string $currentValue): array
diff --git a/src/Capability/Discovery/Discoverer.php b/src/Capability/Discovery/Discoverer.php
index c70559fc..f0a212fd 100644
--- a/src/Capability/Discovery/Discoverer.php
+++ b/src/Capability/Discovery/Discoverer.php
@@ -49,10 +49,13 @@
  */
 final class Discoverer implements DiscovererInterface
 {
+    private readonly DocBlockParser $docBlockParser;
+    private readonly SchemaGeneratorInterface $schemaGenerator;
+
     public function __construct(
         private readonly LoggerInterface $logger = new NullLogger(),
-        private ?DocBlockParser $docBlockParser = null,
-        private ?SchemaGeneratorInterface $schemaGenerator = null,
+        ?DocBlockParser $docBlockParser = null,
+        ?SchemaGeneratorInterface $schemaGenerator = null,
     ) {
         if (!class_exists(Finder::class)) {
             throw new RuntimeException('File-based discovery requires symfony/finder. Run: composer require symfony/finder');
@@ -223,76 +226,65 @@ private function processMethod(\ReflectionMethod $method, array &$discoveredCoun
         try {
             $instance = $attribute->newInstance();
 
-            switch ($attributeClassName) {
-                case McpTool::class:
-                    $name = ElementMetadataResolver::resolveName($method, $instance->name);
-                    $description = ElementMetadataResolver::resolveDescription($method, $instance->description, $this->docBlockParser);
-                    $inputSchema = $this->schemaGenerator->generate($method);
-                    $outputSchema = $this->schemaGenerator->generateOutputSchema($method);
-                    $tool = new Tool(
-                        name: $name,
-                        title: $instance->title,
-                        inputSchema: $inputSchema,
-                        description: $description,
-                        annotations: $instance->annotations,
-                        icons: $instance->icons,
-                        meta: $instance->meta,
-                        outputSchema: $outputSchema,
-                    );
-                    $tools[$name] = new ToolReference($tool, [$className, $methodName]);
-                    ++$discoveredCount['tools'];
-                    break;
-
-                case McpResource::class:
-                    $name = ElementMetadataResolver::resolveName($method, $instance->name);
-                    $description = ElementMetadataResolver::resolveDescription($method, $instance->description, $this->docBlockParser);
-                    $resource = new ResourceDefinition(
-                        $instance->uri,
-                        $name,
-                        $instance->title,
-                        $description,
-                        $instance->mimeType,
-                        $instance->annotations,
-                        $instance->size,
-                        $instance->icons,
-                        $instance->meta,
-                    );
-                    $resources[$instance->uri] = new ResourceReference($resource, [$className, $methodName]);
-
-                    ++$discoveredCount['resources'];
-                    break;
-
-                case McpPrompt::class:
-                    $docBlock = $this->docBlockParser->parseDocBlock($method->getDocComment() ?? null);
-                    $name = ElementMetadataResolver::resolveName($method, $instance->name);
-                    $description = ElementMetadataResolver::resolveDescription($method, $instance->description, $this->docBlockParser);
-                    $arguments = [];
-                    $paramTags = $this->docBlockParser->getParamTags($docBlock);
-                    foreach ($method->getParameters() as $param) {
-                        $reflectionType = $param->getType();
-                        if ($reflectionType instanceof \ReflectionNamedType && !$reflectionType->isBuiltin()) {
-                            continue;
-                        }
-                        $paramTag = $paramTags['$'.$param->getName()] ?? null;
-                        $arguments[] = new PromptArgument($param->getName(), $paramTag ? trim((string) $paramTag->getDescription()) : null, !$param->isOptional() && !$param->isDefaultValueAvailable());
+            if ($instance instanceof McpTool) {
+                $name = ElementMetadataResolver::resolveName($method, $instance->name);
+                $description = ElementMetadataResolver::resolveDescription($method, $instance->description, $this->docBlockParser);
+                $inputSchema = $this->schemaGenerator->generate($method);
+                $outputSchema = $this->schemaGenerator->generateOutputSchema($method);
+                $tool = new Tool(
+                    name: $name,
+                    title: $instance->title,
+                    inputSchema: $inputSchema,
+                    description: $description,
+                    annotations: $instance->annotations,
+                    icons: $instance->icons,
+                    meta: $instance->meta,
+                    outputSchema: $outputSchema,
+                );
+                $tools[$name] = new ToolReference($tool, [$className, $methodName]);
+                ++$discoveredCount['tools'];
+            } elseif ($instance instanceof McpResource) {
+                $name = ElementMetadataResolver::resolveName($method, $instance->name);
+                $description = ElementMetadataResolver::resolveDescription($method, $instance->description, $this->docBlockParser);
+                $resource = new ResourceDefinition(
+                    $instance->uri,
+                    $name,
+                    $instance->title,
+                    $description,
+                    $instance->mimeType,
+                    $instance->annotations,
+                    $instance->size,
+                    $instance->icons,
+                    $instance->meta,
+                );
+                $resources[$instance->uri] = new ResourceReference($resource, [$className, $methodName]);
+
+                ++$discoveredCount['resources'];
+            } elseif ($instance instanceof McpPrompt) {
+                $docBlock = $this->docBlockParser->parseDocBlock($method->getDocComment() ?? null);
+                $name = ElementMetadataResolver::resolveName($method, $instance->name);
+                $description = ElementMetadataResolver::resolveDescription($method, $instance->description, $this->docBlockParser);
+                $arguments = [];
+                $paramTags = $this->docBlockParser->getParamTags($docBlock);
+                foreach ($method->getParameters() as $param) {
+                    $reflectionType = $param->getType();
+                    if ($reflectionType instanceof \ReflectionNamedType && !$reflectionType->isBuiltin()) {
+                        continue;
                     }
-                    $prompt = new Prompt($name, $instance->title, $description, $arguments, $instance->icons, $instance->meta);
-                    $completionProviders = $this->getCompletionProviders($method);
-                    $prompts[$name] = new PromptReference($prompt, [$className, $methodName], $completionProviders);
-                    ++$discoveredCount['prompts'];
-                    break;
-
-                case McpResourceTemplate::class:
-                    $name = ElementMetadataResolver::resolveName($method, $instance->name);
-                    $description = ElementMetadataResolver::resolveDescription($method, $instance->description, $this->docBlockParser);
-                    $mimeType = $instance->mimeType;
-                    $annotations = $instance->annotations;
-                    $meta = $instance->meta ?? null;
-                    $resourceTemplate = new ResourceTemplate($instance->uriTemplate, $name, $instance->title, $description, $mimeType, $annotations, $meta);
-                    $completionProviders = $this->getCompletionProviders($method);
-                    $resourceTemplates[$instance->uriTemplate] = new ResourceTemplateReference($resourceTemplate, [$className, $methodName], $completionProviders);
-                    ++$discoveredCount['resourceTemplates'];
-                    break;
+                    $paramTag = $paramTags['$'.$param->getName()] ?? null;
+                    $arguments[] = new PromptArgument($param->getName(), $paramTag ? trim((string) $paramTag->getDescription()) : null, !$param->isOptional() && !$param->isDefaultValueAvailable());
+                }
+                $prompt = new Prompt($name, $instance->title, $description, $arguments, $instance->icons, $instance->meta);
+                $completionProviders = $this->getCompletionProviders($method);
+                $prompts[$name] = new PromptReference($prompt, [$className, $methodName], $completionProviders);
+                ++$discoveredCount['prompts'];
+            } elseif ($instance instanceof McpResourceTemplate) {
+                $name = ElementMetadataResolver::resolveName($method, $instance->name);
+                $description = ElementMetadataResolver::resolveDescription($method, $instance->description, $this->docBlockParser);
+                $resourceTemplate = new ResourceTemplate($instance->uriTemplate, $name, $instance->title, $description, $instance->mimeType, $instance->annotations, $instance->meta);
+                $completionProviders = $this->getCompletionProviders($method);
+                $resourceTemplates[$instance->uriTemplate] = new ResourceTemplateReference($resourceTemplate, [$className, $methodName], $completionProviders);
+                ++$discoveredCount['resourceTemplates'];
             }
         } catch (ExceptionInterface $e) {
             $this->logger->error("Failed to process MCP attribute on {$className}::{$methodName}", [
@@ -308,7 +300,7 @@ private function processMethod(\ReflectionMethod $method, array &$discoveredCoun
     }
 
     /**
-     * @return array<string, string|ProviderInterface>
+     * @return array<string, class-string<ProviderInterface>|ProviderInterface>
      */
     private function getCompletionProviders(\ReflectionMethod $reflectionMethod): array
     {
@@ -431,17 +423,13 @@ private function getClassFromFile(SplFileInfo $file): ?string
         }
 
         foreach ($potentialClasses as $potentialClass) {
-            if (class_exists($potentialClass, true)) {
+            if (class_exists($potentialClass, true) || interface_exists($potentialClass, true) || trait_exists($potentialClass, true)) {
                 return $potentialClass;
             }
         }
 
         if (!empty($potentialClasses)) {
-            if (!class_exists($potentialClasses[0], false)) {
-                $this->logger->debug('getClassFromFile returning potential non-class type. Are you sure this class has been autoloaded?', ['file' => $file->getPathname(), 'type' => $potentialClasses[0]]);
-            }
-
-            return $potentialClasses[0];
+            $this->logger->debug('getClassFromFile found no loadable type. Are you sure this class has been autoloaded?', ['file' => $file->getPathname(), 'type' => $potentialClasses[0]]);
         }
 
         return null;
diff --git a/src/Capability/Discovery/SchemaGenerator.php b/src/Capability/Discovery/SchemaGenerator.php
index 357c9e98..949ed013 100644
--- a/src/Capability/Discovery/SchemaGenerator.php
+++ b/src/Capability/Discovery/SchemaGenerator.php
@@ -49,12 +49,6 @@
  *     enum?: array<int, int|float|string|null>,
  *     items?: array<string, mixed>,
  * }
- * @phpstan-type VariadicParameterSchema array{
- *     type: 'array',
- *     items?: array<string, mixed>,
- *     description?: string,
- *     parameter_schema?: array<string, mixed>
- * }
  *
  * @author Kyrian Obikwelu <koshnawaza@gmail.com>
  */
@@ -328,7 +322,7 @@ private function buildInferredParameterSchema(array $paramInfo): array
      *
      * @param ParameterInfo $paramInfo
      *
-     * @return VariadicParameterSchema
+     * @return array<string, mixed>
      */
     private function buildVariadicParameterSchema(array $paramInfo): array
     {
@@ -536,7 +530,8 @@ private function parseParametersInfo(\ReflectionMethod|\ReflectionFunction $refl
 
             $paramName = $rp->getName();
             if (\in_array(strtolower($paramName), ['_session', '_request'], true)) {
-                throw new InvalidArgumentException(\sprintf('Handler method "%s::%s" has parameter named "%s" which is not allowed. Please change the name of that parameter.', $reflection->class, $reflection->name, $paramName));
+                $handlerName = $reflection instanceof \ReflectionMethod ? $reflection->class.'::'.$reflection->name : $reflection->name;
+                throw new InvalidArgumentException(\sprintf('Handler "%s" has parameter named "%s" which is not allowed. Please change the name of that parameter.', $handlerName, $paramName));
             }
             $paramTag = $paramTags['$'.$paramName] ?? null;
 
@@ -693,8 +688,10 @@ private function getTypeStringFromReflection(?\ReflectionType $type, bool $nativ
         // Remove leading backslash from class names, but handle built-ins like 'int' or unions like 'int|string'
         if (str_contains($typeString, '\\')) {
             $parts = preg_split('/([|&])/', $typeString, -1, \PREG_SPLIT_DELIM_CAPTURE);
-            $processedParts = array_map(static fn ($part) => str_starts_with($part, '\\') ? ltrim($part, '\\') : $part, $parts);
-            $typeString = implode('', $processedParts);
+            if (false !== $parts) {
+                $processedParts = array_map(static fn ($part) => str_starts_with($part, '\\') ? ltrim($part, '\\') : $part, $parts);
+                $typeString = implode('', $processedParts);
+            }
         }
 
         return $typeString ?: 'mixed';
diff --git a/src/Capability/Discovery/SchemaGeneratorInterface.php b/src/Capability/Discovery/SchemaGeneratorInterface.php
index c21d3cdd..4ee27f86 100644
--- a/src/Capability/Discovery/SchemaGeneratorInterface.php
+++ b/src/Capability/Discovery/SchemaGeneratorInterface.php
@@ -11,9 +11,13 @@
 
 namespace Mcp\Capability\Discovery;
 
+use Mcp\Schema\Tool;
+
 /**
  * Provides JSON Schema generation for reflected elements.
  *
+ * @phpstan-import-type ToolInputSchema from Tool
+ *
  * @author Antoine Bluchet <soyuka@gmail.com>
  */
 interface SchemaGeneratorInterface
@@ -24,11 +28,7 @@ interface SchemaGeneratorInterface
      * The returned schema must be a valid JSON Schema object (type: 'object')
      * with properties corresponding to a tool's parameters.
      *
-     * @return array{
-     *     type: 'object',
-     *     properties: array<string, mixed>|object,
-     *     required?: string[]
-     * }
+     * @return ToolInputSchema
      */
     public function generate(\Reflector $reflection): array;
 
diff --git a/src/Capability/Discovery/SchemaValidator.php b/src/Capability/Discovery/SchemaValidator.php
index 9476d8f8..61215fdd 100644
--- a/src/Capability/Discovery/SchemaValidator.php
+++ b/src/Capability/Discovery/SchemaValidator.php
@@ -160,7 +160,7 @@ private function convertDataForValidator(mixed $data): mixed
     /**
      * Recursively collects leaf validation errors.
      *
-     * @param Error[] $collectedErrors
+     * @param list<Error> $collectedErrors
      */
     private function collectSubErrors(ValidationError $error, array &$collectedErrors): void
     {
@@ -314,13 +314,12 @@ private function formatValidationError(ValidationError $error): string
                 $builtInMessage = $error->message();
                 if ($builtInMessage && 'The data must match the schema' !== $builtInMessage) {
                     $placeholders = $args;
-                    $builtInMessage = preg_replace_callback('/\{(\w+)\}/', static function ($match) use ($placeholders) {
+                    $message = preg_replace_callback('/\{(\w+)\}/', static function (array $match) use ($placeholders): string {
                         $key = $match[1];
                         $value = $placeholders[$key] ?? '{'.$key.'}';
 
-                        return \is_array($value) ? json_encode($value) : (string) $value;
-                    }, $builtInMessage);
-                    $message = $builtInMessage;
+                        return \is_array($value) ? (json_encode($value) ?: '{}') : (string) $value;
+                    }, $builtInMessage) ?? $builtInMessage;
                 }
                 break;
         }
diff --git a/src/Capability/Formatter/ResourceResultFormatter.php b/src/Capability/Formatter/ResourceResultFormatter.php
index bac2bc77..4205933d 100644
--- a/src/Capability/Formatter/ResourceResultFormatter.php
+++ b/src/Capability/Formatter/ResourceResultFormatter.php
@@ -138,7 +138,12 @@ public function format(mixed $readResult, string $uri, ?string $mimeType = null,
 
         if ($readResult instanceof \SplFileInfo && $readResult->isFile() && $readResult->isReadable()) {
             if ($mimeType && str_contains(strtolower($mimeType), 'text')) {
-                return [new TextResourceContents($uri, $mimeType, file_get_contents($readResult->getPathname()), $meta)];
+                $text = file_get_contents($readResult->getPathname());
+                if (false === $text) {
+                    throw new RuntimeException(\sprintf('Could not read file: "%s".', $readResult->getPathname()));
+                }
+
+                return [new TextResourceContents($uri, $mimeType, $text, $meta)];
             }
 
             return [BlobResourceContents::fromSplFileInfo($uri, $readResult, $mimeType, $meta)];
diff --git a/src/Capability/Registry.php b/src/Capability/Registry.php
index 97840431..7d043aae 100644
--- a/src/Capability/Registry.php
+++ b/src/Capability/Registry.php
@@ -245,6 +245,9 @@ public function hasTools(): bool
         return [] !== $this->tools;
     }
 
+    /**
+     * @return Page<Tool>
+     */
     public function getTools(?int $limit = null, ?string $cursor = null): Page
     {
         $this->load();
@@ -283,6 +286,9 @@ public function hasResources(): bool
         return [] !== $this->resources;
     }
 
+    /**
+     * @return Page<ResourceDefinition>
+     */
     public function getResources(?int $limit = null, ?string $cursor = null): Page
     {
         $this->load();
@@ -338,6 +344,9 @@ public function hasResourceTemplates(): bool
         return [] !== $this->resourceTemplates;
     }
 
+    /**
+     * @return Page<ResourceTemplate>
+     */
     public function getResourceTemplates(?int $limit = null, ?string $cursor = null): Page
     {
         $this->load();
@@ -376,6 +385,9 @@ public function hasPrompts(): bool
         return [] !== $this->prompts;
     }
 
+    /**
+     * @return Page<Prompt>
+     */
     public function getPrompts(?int $limit = null, ?string $cursor = null): Page
     {
         $this->load();
@@ -449,11 +461,13 @@ private function calculateNextCursor(int $totalItems, ?string $currentCursor, in
     /**
      * Helper method to paginate results using cursor-based pagination.
      *
-     * @param array<int|string, mixed> $items  The full array of items to paginate The full array of items to paginate
-     * @param int                      $limit  Maximum number of items to return
-     * @param string|null              $cursor Base64 encoded offset position
+     * @template T
+     *
+     * @param array<int|string, T> $items  The full array of items to paginate
+     * @param int                  $limit  Maximum number of items to return
+     * @param string|null          $cursor Base64 encoded offset position
      *
-     * @return array<int|string, mixed> Paginated results
+     * @return list<T> Paginated results
      *
      * @throws InvalidCursorException When cursor is invalid (MCP error code -32602)
      */
diff --git a/src/Capability/Registry/Loader/ReflectedElementLoader.php b/src/Capability/Registry/Loader/ReflectedElementLoader.php
index 209644c7..2d6257f9 100644
--- a/src/Capability/Registry/Loader/ReflectedElementLoader.php
+++ b/src/Capability/Registry/Loader/ReflectedElementLoader.php
@@ -104,7 +104,8 @@ public function load(RegistryInterface $registry): void
                 $reflection = HandlerResolver::resolve($data['handler']);
 
                 if ($reflection instanceof \ReflectionFunction) {
-                    $name = $data['name'] ?? 'closure_tool_'.spl_object_id($data['handler']);
+                    $handler = $data['handler'];
+                    $name = $data['name'] ?? ($handler instanceof \Closure ? 'closure_tool_'.spl_object_id($handler) : $reflection->getName());
                     $description = $data['description'] ?? null;
                 } else {
                     $name = ElementMetadataResolver::resolveName($reflection, $data['name'] ?? null);
@@ -142,7 +143,8 @@ public function load(RegistryInterface $registry): void
                 $reflection = HandlerResolver::resolve($data['handler']);
 
                 if ($reflection instanceof \ReflectionFunction) {
-                    $name = $data['name'] ?? 'closure_resource_'.spl_object_id($data['handler']);
+                    $handler = $data['handler'];
+                    $name = $data['name'] ?? ($handler instanceof \Closure ? 'closure_resource_'.spl_object_id($handler) : $reflection->getName());
                     $description = $data['description'] ?? null;
                 } else {
                     $name = ElementMetadataResolver::resolveName($reflection, $data['name'] ?? null);
@@ -179,7 +181,8 @@ public function load(RegistryInterface $registry): void
                 $reflection = HandlerResolver::resolve($data['handler']);
 
                 if ($reflection instanceof \ReflectionFunction) {
-                    $name = $data['name'] ?? 'closure_template_'.spl_object_id($data['handler']);
+                    $handler = $data['handler'];
+                    $name = $data['name'] ?? ($handler instanceof \Closure ? 'closure_template_'.spl_object_id($handler) : $reflection->getName());
                     $description = $data['description'] ?? null;
                 } else {
                     $name = ElementMetadataResolver::resolveName($reflection, $data['name'] ?? null);
@@ -215,7 +218,8 @@ public function load(RegistryInterface $registry): void
                 $reflection = HandlerResolver::resolve($data['handler']);
 
                 if ($reflection instanceof \ReflectionFunction) {
-                    $name = $data['name'] ?? 'closure_prompt_'.spl_object_id($data['handler']);
+                    $handler = $data['handler'];
+                    $name = $data['name'] ?? ($handler instanceof \Closure ? 'closure_prompt_'.spl_object_id($handler) : $reflection->getName());
                     $description = $data['description'] ?? null;
                 } else {
                     $name = ElementMetadataResolver::resolveName($reflection, $data['name'] ?? null);
diff --git a/src/Capability/Registry/ReferenceHandler.php b/src/Capability/Registry/ReferenceHandler.php
index c0084cbf..ff10de31 100644
--- a/src/Capability/Registry/ReferenceHandler.php
+++ b/src/Capability/Registry/ReferenceHandler.php
@@ -48,7 +48,11 @@ public function handle(ElementReference $reference, array $arguments): mixed
                 $instance = $this->getClassInstance($reference->handler);
                 $arguments = $this->prepareArguments($reflection, $arguments);
 
-                return \call_user_func($instance, ...$arguments);
+                if (!\is_callable($instance)) {
+                    throw new InvalidArgumentException(\sprintf('Handler "%s" is not invokable.', $reference->handler));
+                }
+
+                return $instance(...$arguments);
             }
 
             if (\function_exists($reference->handler)) {
@@ -67,12 +71,17 @@ public function handle(ElementReference $reference, array $arguments): mixed
         }
 
         if (\is_array($reference->handler)) {
-            [$className, $methodName] = $reference->handler;
-            $reflection = new \ReflectionMethod($className, $methodName);
-            $instance = $this->getClassInstance($className);
+            [$classOrObject, $methodName] = $reference->handler;
+            $reflection = new \ReflectionMethod($classOrObject, $methodName);
+            $instance = \is_object($classOrObject) ? $classOrObject : $this->getClassInstance($classOrObject);
             $arguments = $this->prepareArguments($reflection, $arguments);
 
-            return \call_user_func([$instance, $methodName], ...$arguments);
+            $callable = [$instance, $methodName];
+            if (!\is_callable($callable)) {
+                throw new InvalidArgumentException(\sprintf('Handler "%s::%s" is not callable.', $instance::class, $methodName));
+            }
+
+            return $callable(...$arguments);
         }
 
         throw new InvalidArgumentException('Invalid handler type');
diff --git a/src/Capability/Registry/ResourceTemplateReference.php b/src/Capability/Registry/ResourceTemplateReference.php
index 49d03b39..925550f5 100644
--- a/src/Capability/Registry/ResourceTemplateReference.php
+++ b/src/Capability/Registry/ResourceTemplateReference.php
@@ -12,6 +12,7 @@
 namespace Mcp\Capability\Registry;
 
 use Mcp\Capability\Formatter\ResourceResultFormatter;
+use Mcp\Exception\InvalidArgumentException;
 use Mcp\Schema\Content\ResourceContents;
 use Mcp\Schema\ResourceTemplate;
 
@@ -97,6 +98,10 @@ private function compileTemplate(): void
 
         $segments = preg_split('/(\{\w+\})/', $this->resourceTemplate->uriTemplate, -1, \PREG_SPLIT_DELIM_CAPTURE | \PREG_SPLIT_NO_EMPTY);
 
+        if (false === $segments) {
+            throw new InvalidArgumentException(\sprintf('Invalid URI template "%s".', $this->resourceTemplate->uriTemplate));
+        }
+
         foreach ($segments as $segment) {
             if (preg_match('/^\{(\w+)\}$/', $segment, $matches)) {
                 $varName = $matches[1];
diff --git a/src/Capability/RegistryInterface.php b/src/Capability/RegistryInterface.php
index bbbef766..94b0db23 100644
--- a/src/Capability/RegistryInterface.php
+++ b/src/Capability/RegistryInterface.php
@@ -112,6 +112,8 @@ public function hasTools(): bool;
 
     /**
      * Gets all registered tools.
+     *
+     * @return Page<Tool>
      */
     public function getTools(?int $limit = null, ?string $cursor = null): Page;
 
@@ -129,6 +131,8 @@ public function hasResources(): bool;
 
     /**
      * Gets all registered resources.
+     *
+     * @return Page<ResourceDefinition>
      */
     public function getResources(?int $limit = null, ?string $cursor = null): Page;
 
@@ -146,6 +150,8 @@ public function hasResourceTemplates(): bool;
 
     /**
      * Gets all registered resource templates.
+     *
+     * @return Page<ResourceTemplate>
      */
     public function getResourceTemplates(?int $limit = null, ?string $cursor = null): Page;
 
@@ -163,6 +169,8 @@ public function hasPrompts(): bool;
 
     /**
      * Gets all registered prompts.
+     *
+     * @return Page<Prompt>
      */
     public function getPrompts(?int $limit = null, ?string $cursor = null): Page;
 
diff --git a/src/Client.php b/src/Client.php
index 5e40cad2..66507ffe 100644
--- a/src/Client.php
+++ b/src/Client.php
@@ -280,6 +280,10 @@ public function listResourceTemplates(?string $cursor = null): ListResourceTempl
      */
     public function readResource(string $uri, ?callable $onProgress = null): ReadResourceResult
     {
+        if ('' === $uri) {
+            throw new InvalidArgumentException('Resource URI must not be empty.');
+        }
+
         $request = new ReadResourceRequest($uri);
 
         $response = $this->sendRequest($request, $onProgress);
@@ -373,13 +377,14 @@ public function sendRootsListChanged(): void
      */
     private function sendRequest(Request $request, ?callable $onProgress = null, ?CancellationTokenInterface $cancellation = null, ?float $timeoutSeconds = null): Response
     {
-        if (!$this->isConnected()) {
+        $transport = $this->transport;
+        if (null === $transport || !$this->protocol->getState()->isInitialized()) {
             throw new ConnectionException('Client is not connected. Call connect() first.');
         }
 
         $withProgress = null !== $onProgress;
         $fiber = new \Fiber(fn () => $this->protocol->request($request, $this->config->requestTimeout, $withProgress, $cancellation, $timeoutSeconds));
-        $response = $this->transport->runRequest($fiber, $onProgress);
+        $response = $transport->runRequest($fiber, $onProgress);
 
         if ($response instanceof Error) {
             throw RequestException::fromError($response);
diff --git a/src/Client/Stateless/ToolCatalog.php b/src/Client/Stateless/ToolCatalog.php
index 3348db00..0e35570a 100644
--- a/src/Client/Stateless/ToolCatalog.php
+++ b/src/Client/Stateless/ToolCatalog.php
@@ -32,7 +32,7 @@
  */
 final class ToolCatalog
 {
-    /** @var array<string, array<string, mixed>> tool name to input schema */
+    /** @var array<string, array<mixed>> tool name to input schema */
     private array $schemas = [];
 
     /** @var array<string, string> tool name to the reason it was refused */
@@ -50,17 +50,17 @@ public function __construct(
      * is how the client "rejects" it: it never reaches the caller, so it cannot
      * be called, and the tools listed beside it are untouched.
      *
-     * @param list<array<string, mixed>> $tools raw `tools/list` entries
+     * @param array<mixed> $tools raw `tools/list` entries
      *
-     * @return list<array<string, mixed>>
+     * @return list<mixed>
      */
     public function record(array $tools): array
     {
         $usable = [];
 
         foreach ($tools as $tool) {
-            $name = $tool['name'] ?? null;
-            $schema = $tool['inputSchema'] ?? null;
+            $name = \is_array($tool) ? $tool['name'] ?? null : null;
+            $schema = \is_array($tool) ? $tool['inputSchema'] ?? null : null;
 
             if (!\is_string($name) || !\is_array($schema)) {
                 $usable[] = $tool;
diff --git a/src/Client/Transport/HttpTransport.php b/src/Client/Transport/HttpTransport.php
index 8fd07be9..53596bc9 100644
--- a/src/Client/Transport/HttpTransport.php
+++ b/src/Client/Transport/HttpTransport.php
@@ -114,15 +114,16 @@ public function __construct(
 
     public function connect(): void
     {
-        $this->activeFiber = new \Fiber(fn () => $this->handleInitialize());
+        $fiber = new \Fiber(fn () => $this->handleInitialize());
+        $this->activeFiber = $fiber;
 
-        $this->activeFiber->start();
+        $fiber->start();
 
-        while (!$this->activeFiber->isTerminated()) {
+        while (!$fiber->isTerminated()) {
             $this->tick();
         }
 
-        $result = $this->activeFiber->getReturn();
+        $result = $fiber->getReturn();
         $this->activeFiber = null;
 
         if ($result instanceof Error) {
diff --git a/src/Client/Transport/StdioTransport.php b/src/Client/Transport/StdioTransport.php
index 314da718..c2be50e4 100644
--- a/src/Client/Transport/StdioTransport.php
+++ b/src/Client/Transport/StdioTransport.php
@@ -94,15 +94,16 @@ public function connect(): void
     {
         $this->spawnProcess();
 
-        $this->activeFiber = new \Fiber(fn () => $this->handleInitialize());
+        $fiber = new \Fiber(fn () => $this->handleInitialize());
+        $this->activeFiber = $fiber;
 
-        $this->activeFiber->start();
+        $fiber->start();
 
-        while (!$this->activeFiber->isTerminated()) {
+        while (!$fiber->isTerminated()) {
             $this->tick();
         }
 
-        $result = $this->activeFiber->getReturn();
+        $result = $fiber->getReturn();
         $this->activeFiber = null;
 
         if ($result instanceof Error) {
@@ -184,7 +185,7 @@ private function spawnProcess(): void
             $cmd .= ' '.escapeshellarg($arg);
         }
 
-        $this->process = proc_open(
+        $process = proc_open(
             $cmd,
             $descriptors,
             $pipes,
@@ -192,10 +193,12 @@ private function spawnProcess(): void
             $this->env
         );
 
-        if (!\is_resource($this->process)) {
+        if (!\is_resource($process)) {
             throw new ConnectionException('Failed to start process: '.$cmd);
         }
 
+        $this->process = $process;
+
         $this->stdin = $pipes[0];
         $this->stdout = $pipes[1];
         $this->stderr = $pipes[2];
diff --git a/src/Schema/ClientCapabilities.php b/src/Schema/ClientCapabilities.php
index 75d50ff6..88ea3f6e 100644
--- a/src/Schema/ClientCapabilities.php
+++ b/src/Schema/ClientCapabilities.php
@@ -146,11 +146,11 @@ public function withExtensions(array $extensions): self
 
     /**
      * @return array{
-     *     roots?: object,
-     *     sampling?: object,
-     *     elicitation?: object,
-     *     experimental?: object,
-     *     extensions?: object,
+     *     roots?: \stdClass,
+     *     sampling?: \stdClass,
+     *     elicitation?: \stdClass,
+     *     experimental?: \stdClass,
+     *     extensions?: \stdClass,
      * }|\stdClass
      */
     public function jsonSerialize(): array|object
diff --git a/src/Schema/Content/AudioContent.php b/src/Schema/Content/AudioContent.php
index cf7418c5..517be814 100644
--- a/src/Schema/Content/AudioContent.php
+++ b/src/Schema/Content/AudioContent.php
@@ -40,7 +40,7 @@ public function __construct(
     }
 
     /**
-     * @param AudioContentData $data
+     * @param AudioContentData|array<mixed> $data
      */
     public static function fromArray(array $data): self
     {
diff --git a/src/Schema/Content/BlobResourceContents.php b/src/Schema/Content/BlobResourceContents.php
index ee126fbc..24c342ca 100644
--- a/src/Schema/Content/BlobResourceContents.php
+++ b/src/Schema/Content/BlobResourceContents.php
@@ -43,7 +43,7 @@ public function __construct(
     }
 
     /**
-     * @param BlobResourceContentsData $data
+     * @param BlobResourceContentsData|array<mixed> $data
      */
     public static function fromArray(array $data): self
     {
@@ -71,6 +71,9 @@ public static function fromArray(array $data): self
     public static function fromStream(string $uri, $stream, string $mimeType, ?array $meta = null): self
     {
         $blob = stream_get_contents($stream);
+        if (false === $blob) {
+            throw new InvalidArgumentException('Could not read stream.');
+        }
 
         return new self($uri, $mimeType, base64_encode($blob), $meta);
     }
@@ -80,8 +83,11 @@ public static function fromStream(string $uri, $stream, string $mimeType, ?array
      * */
     public static function fromSplFileInfo(string $uri, \SplFileInfo $file, ?string $explicitMimeType = null, ?array $meta = null): self
     {
-        $mimeType = $explicitMimeType ?? mime_content_type($file->getPathname());
+        $mimeType = $explicitMimeType ?? (mime_content_type($file->getPathname()) ?: null);
         $blob = file_get_contents($file->getPathname());
+        if (false === $blob) {
+            throw new InvalidArgumentException(\sprintf('Could not read file: "%s".', $file->getPathname()));
+        }
 
         return new self($uri, $mimeType, base64_encode($blob), $meta);
     }
diff --git a/src/Schema/Content/EmbeddedResource.php b/src/Schema/Content/EmbeddedResource.php
index 76c4d679..eb772c03 100644
--- a/src/Schema/Content/EmbeddedResource.php
+++ b/src/Schema/Content/EmbeddedResource.php
@@ -40,7 +40,7 @@ public function __construct(
     }
 
     /**
-     * @param EmbeddedResourceData $data
+     * @param EmbeddedResourceData|array<mixed> $data
      */
     public static function fromArray(array $data): self
     {
@@ -121,7 +121,7 @@ public static function fromSplFileInfo(string $uri, \SplFileInfo $file, ?string
             throw new RuntimeException(\sprintf('Could not read file: "%s".', $file->getPathname()));
         }
 
-        return new self(new BlobResourceContents($uri, $explicitMimeType ?? mime_content_type($file->getPathname()), base64_encode($content)), $annotations);
+        return new self(new BlobResourceContents($uri, $explicitMimeType ?? (mime_content_type($file->getPathname()) ?: null), base64_encode($content)), $annotations);
     }
 
     /**
@@ -134,7 +134,7 @@ public static function fromSplFileInfo(string $uri, \SplFileInfo $file, ?string
     public function jsonSerialize(): array
     {
         $data = [
-            'type' => $this->type,
+            'type' => 'resource',
             'resource' => $this->resource,
         ];
         if (null !== $this->annotations) {
diff --git a/src/Schema/Content/ImageContent.php b/src/Schema/Content/ImageContent.php
index 9e2cbffd..3f7ada58 100644
--- a/src/Schema/Content/ImageContent.php
+++ b/src/Schema/Content/ImageContent.php
@@ -44,7 +44,7 @@ public function __construct(
     }
 
     /**
-     * @param ImageContentData $data
+     * @param ImageContentData|array<mixed> $data
      */
     public static function fromArray(array $data): self
     {
@@ -77,7 +77,12 @@ public static function fromFile(string $path, ?string $mimeType = null, ?Annotat
             throw new InvalidArgumentException(\sprintf('Image file not found: "%s".', $path));
         }
 
-        $data = base64_encode(file_get_contents($path));
+        $contents = file_get_contents($path);
+        if (false === $contents) {
+            throw new InvalidArgumentException(\sprintf('Could not read image file: "%s".', $path));
+        }
+
+        $data = base64_encode($contents);
         $detectedMime = $mimeType ?? mime_content_type($path) ?: 'image/png';
 
         return new self($data, $detectedMime, $annotations);
@@ -101,7 +106,7 @@ public static function fromString(string $data, string $mimeType, ?Annotations $
     public function jsonSerialize(): array
     {
         $result = [
-            'type' => $this->type,
+            'type' => 'image',
             'data' => $this->data,
             'mimeType' => $this->mimeType,
         ];
diff --git a/src/Schema/Content/PromptMessage.php b/src/Schema/Content/PromptMessage.php
index d47f5ec9..e54f6583 100644
--- a/src/Schema/Content/PromptMessage.php
+++ b/src/Schema/Content/PromptMessage.php
@@ -46,7 +46,7 @@ public function __construct(
     }
 
     /**
-     * @param PromptMessageData $data
+     * @param PromptMessageData|array<mixed> $data
      */
     public static function fromArray(array $data): self
     {
diff --git a/src/Schema/Content/ResourceLink.php b/src/Schema/Content/ResourceLink.php
index 946c9b82..6d8f0756 100644
--- a/src/Schema/Content/ResourceLink.php
+++ b/src/Schema/Content/ResourceLink.php
@@ -68,7 +68,7 @@ public function __construct(
     }
 
     /**
-     * @param ResourceLinkData $data
+     * @param ResourceLinkData|array<mixed> $data
      */
     public static function fromArray(array $data): self
     {
@@ -124,7 +124,7 @@ public static function fromArray(array $data): self
     public function jsonSerialize(): array
     {
         $data = [
-            'type' => $this->type,
+            'type' => 'resource_link',
             'uri' => $this->uri,
             'name' => $this->name,
         ];
diff --git a/src/Schema/Content/SamplingMessage.php b/src/Schema/Content/SamplingMessage.php
index 17343d06..c4af551c 100644
--- a/src/Schema/Content/SamplingMessage.php
+++ b/src/Schema/Content/SamplingMessage.php
@@ -81,7 +81,7 @@ public function getContentBlocks(): array
     }
 
     /**
-     * @param SamplingMessageData $data
+     * @param SamplingMessageData|array<mixed> $data
      */
     public static function fromArray(array $data): self
     {
diff --git a/src/Schema/Content/TextContent.php b/src/Schema/Content/TextContent.php
index b743af57..54b1cde2 100644
--- a/src/Schema/Content/TextContent.php
+++ b/src/Schema/Content/TextContent.php
@@ -46,7 +46,7 @@ public function __construct(
     }
 
     /**
-     * @param TextContentData $data
+     * @param TextContentData|array<mixed> $data
      */
     public static function fromArray(array $data): self
     {
diff --git a/src/Schema/Content/TextResourceContents.php b/src/Schema/Content/TextResourceContents.php
index 9beff811..61493338 100644
--- a/src/Schema/Content/TextResourceContents.php
+++ b/src/Schema/Content/TextResourceContents.php
@@ -43,7 +43,7 @@ public function __construct(
     }
 
     /**
-     * @param TextResourceContentsData $data
+     * @param TextResourceContentsData|array<mixed> $data
      */
     public static function fromArray(array $data): self
     {
diff --git a/src/Schema/Content/ToolResultContent.php b/src/Schema/Content/ToolResultContent.php
index 7f2b11c1..87f46a29 100644
--- a/src/Schema/Content/ToolResultContent.php
+++ b/src/Schema/Content/ToolResultContent.php
@@ -99,7 +99,7 @@ public static function fromArray(array $data): self
     public function jsonSerialize(): array
     {
         $data = [
-            'type' => $this->type,
+            'type' => 'tool_result',
             'toolUseId' => $this->toolUseId,
             'content' => $this->content,
         ];
diff --git a/src/Schema/Content/ToolUseContent.php b/src/Schema/Content/ToolUseContent.php
index 8952e8cb..d0401111 100644
--- a/src/Schema/Content/ToolUseContent.php
+++ b/src/Schema/Content/ToolUseContent.php
@@ -70,7 +70,7 @@ public static function fromArray(array $data): self
     public function jsonSerialize(): array
     {
         $data = [
-            'type' => $this->type,
+            'type' => 'tool_use',
             'id' => $this->id,
             'name' => $this->name,
             'input' => $this->input ?: new \stdClass(),
diff --git a/src/Schema/Elicitation/AbstractSchemaDefinition.php b/src/Schema/Elicitation/AbstractSchemaDefinition.php
index d202e068..f6698b2c 100644
--- a/src/Schema/Elicitation/AbstractSchemaDefinition.php
+++ b/src/Schema/Elicitation/AbstractSchemaDefinition.php
@@ -43,7 +43,7 @@ protected static function validateTitle(array $data, string $schemaType): void
     /**
      * Build the base JSON structure with type, optional title and description.
      *
-     * @return array<string, mixed>
+     * @return array{type: string, title?: string, description?: string}
      */
     protected function buildBaseJson(string $type): array
     {
diff --git a/src/Schema/Elicitation/BooleanSchemaDefinition.php b/src/Schema/Elicitation/BooleanSchemaDefinition.php
index dfec206f..3c85e799 100644
--- a/src/Schema/Elicitation/BooleanSchemaDefinition.php
+++ b/src/Schema/Elicitation/BooleanSchemaDefinition.php
@@ -36,7 +36,7 @@ public function __construct(
      *     title?: string,
      *     description?: string,
      *     default?: bool,
-     * } $data
+     * }|array<mixed> $data
      */
     public static function fromArray(array $data): self
     {
diff --git a/src/Schema/Elicitation/ElicitationSchema.php b/src/Schema/Elicitation/ElicitationSchema.php
index f41b9c27..720c0ca3 100644
--- a/src/Schema/Elicitation/ElicitationSchema.php
+++ b/src/Schema/Elicitation/ElicitationSchema.php
@@ -51,7 +51,7 @@ public function __construct(
      *     type?: string,
      *     properties: array<string, array{type: string, title: string, ...}>,
      *     required?: string[],
-     * } $data
+     * }|array<mixed> $data
      */
     public static function fromArray(array $data): self
     {
diff --git a/src/Schema/Elicitation/EnumSchemaDefinition.php b/src/Schema/Elicitation/EnumSchemaDefinition.php
index 7a3149f1..6127fd99 100644
--- a/src/Schema/Elicitation/EnumSchemaDefinition.php
+++ b/src/Schema/Elicitation/EnumSchemaDefinition.php
@@ -64,7 +64,7 @@ public function __construct(
      *     description?: string,
      *     default?: string,
      *     enumNames?: string[],
-     * } $data
+     * }|array<mixed> $data
      */
     public static function fromArray(array $data): self
     {
diff --git a/src/Schema/Elicitation/MultiSelectEnumSchemaDefinition.php b/src/Schema/Elicitation/MultiSelectEnumSchemaDefinition.php
index cd68c6c4..996eced9 100644
--- a/src/Schema/Elicitation/MultiSelectEnumSchemaDefinition.php
+++ b/src/Schema/Elicitation/MultiSelectEnumSchemaDefinition.php
@@ -79,7 +79,7 @@ public function __construct(
      *     default?: string[],
      *     minItems?: int,
      *     maxItems?: int,
-     * } $data
+     * }|array<mixed> $data
      */
     public static function fromArray(array $data): self
     {
diff --git a/src/Schema/Elicitation/NumberSchemaDefinition.php b/src/Schema/Elicitation/NumberSchemaDefinition.php
index 3375f206..18ddfc38 100644
--- a/src/Schema/Elicitation/NumberSchemaDefinition.php
+++ b/src/Schema/Elicitation/NumberSchemaDefinition.php
@@ -65,7 +65,7 @@ public function __construct(
      *     default?: int|float,
      *     minimum?: int|float,
      *     maximum?: int|float,
-     * } $data
+     * }|array<mixed> $data
      */
     public static function fromArray(array $data): self
     {
diff --git a/src/Schema/Elicitation/StringSchemaDefinition.php b/src/Schema/Elicitation/StringSchemaDefinition.php
index 3347ea30..e04f5c4d 100644
--- a/src/Schema/Elicitation/StringSchemaDefinition.php
+++ b/src/Schema/Elicitation/StringSchemaDefinition.php
@@ -67,7 +67,7 @@ public function __construct(
      *     format?: string,
      *     minLength?: int,
      *     maxLength?: int,
-     * } $data
+     * }|array<mixed> $data
      */
     public static function fromArray(array $data): self
     {
diff --git a/src/Schema/Elicitation/TitledEnumSchemaDefinition.php b/src/Schema/Elicitation/TitledEnumSchemaDefinition.php
index 41c92422..334e0bcd 100644
--- a/src/Schema/Elicitation/TitledEnumSchemaDefinition.php
+++ b/src/Schema/Elicitation/TitledEnumSchemaDefinition.php
@@ -24,14 +24,19 @@
 final class TitledEnumSchemaDefinition extends AbstractSchemaDefinition
 {
     /**
-     * @param ?string                                   $title       Optional human-readable title for the field
-     * @param list<array{const: string, title: string}> $oneOf       Array of const/title pairs
-     * @param string|null                               $description Optional description/help text
-     * @param string|null                               $default     Optional default value (must match a const)
+     * @var list<array{const: string, title: string}>
+     */
+    public readonly array $oneOf;
+
+    /**
+     * @param ?string      $title       Optional human-readable title for the field
+     * @param array<mixed> $oneOf       Array of const/title pairs
+     * @param string|null  $description Optional description/help text
+     * @param string|null  $default     Optional default value (must match a const)
      */
     public function __construct(
         ?string $title,
-        public readonly array $oneOf,
+        array $oneOf,
         ?string $description = null,
         public readonly ?string $default = null,
     ) {
@@ -42,16 +47,20 @@ public function __construct(
         }
 
         $consts = [];
+        $pairs = [];
         foreach ($oneOf as $item) {
-            if (!isset($item['const']) || !\is_string($item['const'])) {
+            if (!\is_array($item) || !isset($item['const']) || !\is_string($item['const'])) {
                 throw new InvalidArgumentException('Each oneOf item must have a string "const" property.');
             }
             if (!isset($item['title']) || !\is_string($item['title'])) {
                 throw new InvalidArgumentException('Each oneOf item must have a string "title" property.');
             }
             $consts[] = $item['const'];
+            $pairs[] = ['const' => $item['const'], 'title' => $item['title']];
         }
 
+        $this->oneOf = $pairs;
+
         if (null !== $default && !\in_array($default, $consts, true)) {
             throw new InvalidArgumentException(\sprintf('Default value "%s" is not in the oneOf const values.', $default));
         }
@@ -63,7 +72,7 @@ public function __construct(
      *     oneOf: list<array{const: string, title: string}>,
      *     description?: string,
      *     default?: string,
-     * } $data
+     * }|array<mixed> $data
      */
     public static function fromArray(array $data): self
     {
diff --git a/src/Schema/Elicitation/TitledMultiSelectEnumSchemaDefinition.php b/src/Schema/Elicitation/TitledMultiSelectEnumSchemaDefinition.php
index 17f18995..ee7241d1 100644
--- a/src/Schema/Elicitation/TitledMultiSelectEnumSchemaDefinition.php
+++ b/src/Schema/Elicitation/TitledMultiSelectEnumSchemaDefinition.php
@@ -23,16 +23,21 @@
 final class TitledMultiSelectEnumSchemaDefinition extends AbstractSchemaDefinition
 {
     /**
-     * @param ?string                                   $title       Optional human-readable title for the field
-     * @param list<array{const: string, title: string}> $anyOf       Array of const/title pairs
-     * @param string|null                               $description Optional description/help text
-     * @param string[]|null                             $default     Optional default selected values (must be subset of anyOf consts)
-     * @param int|null                                  $minItems    Optional minimum number of selections
-     * @param int|null                                  $maxItems    Optional maximum number of selections
+     * @var list<array{const: string, title: string}>
+     */
+    public readonly array $anyOf;
+
+    /**
+     * @param ?string       $title       Optional human-readable title for the field
+     * @param array<mixed>  $anyOf       Array of const/title pairs
+     * @param string|null   $description Optional description/help text
+     * @param string[]|null $default     Optional default selected values (must be subset of anyOf consts)
+     * @param int|null      $minItems    Optional minimum number of selections
+     * @param int|null      $maxItems    Optional maximum number of selections
      */
     public function __construct(
         ?string $title,
-        public readonly array $anyOf,
+        array $anyOf,
         ?string $description = null,
         public readonly ?array $default = null,
         public readonly ?int $minItems = null,
@@ -45,16 +50,20 @@ public function __construct(
         }
 
         $consts = [];
+        $pairs = [];
         foreach ($anyOf as $item) {
-            if (!isset($item['const']) || !\is_string($item['const'])) {
+            if (!\is_array($item) || !isset($item['const']) || !\is_string($item['const'])) {
                 throw new InvalidArgumentException('Each anyOf item must have a string "const" property.');
             }
             if (!isset($item['title']) || !\is_string($item['title'])) {
                 throw new InvalidArgumentException('Each anyOf item must have a string "title" property.');
             }
             $consts[] = $item['const'];
+            $pairs[] = ['const' => $item['const'], 'title' => $item['title']];
         }
 
+        $this->anyOf = $pairs;
+
         if (null !== $minItems && $minItems < 0) {
             throw new InvalidArgumentException('minItems must be non-negative.');
         }
@@ -84,7 +93,7 @@ public function __construct(
      *     default?: string[],
      *     minItems?: int,
      *     maxItems?: int,
-     * } $data
+     * }|array<mixed> $data
      */
     public static function fromArray(array $data): self
     {
diff --git a/src/Schema/Enum/ProtocolVersion.php b/src/Schema/Enum/ProtocolVersion.php
index 03ebddfd..c0666b88 100644
--- a/src/Schema/Enum/ProtocolVersion.php
+++ b/src/Schema/Enum/ProtocolVersion.php
@@ -80,7 +80,13 @@ public static function latestHandshake(): self
      */
     public static function handshakeVersions(): array
     {
-        return array_values(array_filter(self::cases(), static fn (self $v): bool => !$v->isModern()));
+        $versions = array_values(array_filter(self::cases(), static fn (self $v): bool => !$v->isModern()));
+
+        if ([] === $versions) {
+            throw new LogicException('No handshake-era protocol revision is declared.');
+        }
+
+        return $versions;
     }
 
     /**
@@ -90,7 +96,13 @@ public static function handshakeVersions(): array
      */
     public static function modernVersions(): array
     {
-        return array_values(array_filter(self::cases(), static fn (self $v): bool => $v->isModern()));
+        $versions = array_values(array_filter(self::cases(), static fn (self $v): bool => $v->isModern()));
+
+        if ([] === $versions) {
+            throw new LogicException('No modern-era protocol revision is declared.');
+        }
+
+        return $versions;
     }
 
     /**
diff --git a/src/Schema/Extension/Apps/UiToolMeta.php b/src/Schema/Extension/Apps/UiToolMeta.php
index 235df2a4..39edd8f3 100644
--- a/src/Schema/Extension/Apps/UiToolMeta.php
+++ b/src/Schema/Extension/Apps/UiToolMeta.php
@@ -50,7 +50,7 @@ public static function fromArray(array $data): self
 
         return new self(
             resourceUri: $data['resourceUri'] ?? null,
-            visibility: isset($data['visibility']) ? array_map(
+            visibility: isset($data['visibility']) ? array_values(array_map(
                 static function (mixed $entry): ToolVisibility {
                     if (!\is_string($entry) || null === $case = ToolVisibility::tryFrom($entry)) {
                         throw new InvalidArgumentException('Each entry in "visibility" of UiToolMeta data must be a valid tool visibility.');
@@ -59,7 +59,7 @@ static function (mixed $entry): ToolVisibility {
                     return $case;
                 },
                 $data['visibility'],
-            ) : null,
+            )) : null,
         );
     }
 
diff --git a/src/Schema/Icon.php b/src/Schema/Icon.php
index 27513435..71bddfd7 100644
--- a/src/Schema/Icon.php
+++ b/src/Schema/Icon.php
@@ -63,7 +63,7 @@ public function __construct(
     }
 
     /**
-     * @param IconData $data
+     * @param IconData|array<mixed> $data
      */
     public static function fromArray(array $data): self
     {
diff --git a/src/Schema/Implementation.php b/src/Schema/Implementation.php
index b48be544..2cbeb4d3 100644
--- a/src/Schema/Implementation.php
+++ b/src/Schema/Implementation.php
@@ -44,7 +44,7 @@ public function __construct(
      *     icons?: IconData[],
      *     websiteUrl?: string,
      *     title?: string,
-     * } $data
+     * }|array<mixed> $data
      */
     public static function fromArray(array $data): self
     {
@@ -55,12 +55,13 @@ public static function fromArray(array $data): self
             throw new InvalidArgumentException('Invalid or missing "version" in Implementation data.');
         }
 
+        $icons = null;
         if (isset($data['icons'])) {
             if (!\is_array($data['icons'])) {
                 throw new InvalidArgumentException('Invalid "icons" in Implementation data; expected an array.');
             }
 
-            $data['icons'] = Icon::listFromArray($data['icons'], 'Implementation');
+            $icons = Icon::listFromArray($data['icons'], 'Implementation');
         }
 
         if (isset($data['description']) && !\is_string($data['description'])) {
@@ -77,7 +78,7 @@ public static function fromArray(array $data): self
             $data['name'],
             $data['version'],
             $data['description'] ?? null,
-            $data['icons'] ?? null,
+            $icons,
             $data['websiteUrl'] ?? null,
             $data['title'] ?? null,
         );
diff --git a/src/Schema/JsonRpc/Error.php b/src/Schema/JsonRpc/Error.php
index 7749fa8f..dea975c7 100644
--- a/src/Schema/JsonRpc/Error.php
+++ b/src/Schema/JsonRpc/Error.php
@@ -73,7 +73,7 @@ public function __construct(
     }
 
     /**
-     * @param ErrorData $data
+     * @param ErrorData|array<mixed> $data
      */
     final public static function fromArray(array $data): self
     {
diff --git a/src/Schema/JsonRpc/Response.php b/src/Schema/JsonRpc/Response.php
index 4c64881e..c3bcbdbc 100644
--- a/src/Schema/JsonRpc/Response.php
+++ b/src/Schema/JsonRpc/Response.php
@@ -47,7 +47,7 @@ public function getId(): string|int
     }
 
     /**
-     * @param ResponseData $data
+     * @param ResponseData|array<mixed> $data
      *
      * @return self<array<string, mixed>>
      */
@@ -69,7 +69,10 @@ public static function fromArray(array $data): self
             throw new InvalidArgumentException('Response "result" must be an array.');
         }
 
-        return new self($data['id'], $data['result']);
+        /** @var array<string, mixed> $result A result decoded from a JSON object is string-keyed. */
+        $result = $data['result'];
+
+        return new self($data['id'], $result);
     }
 
     /**
diff --git a/src/Schema/Page.php b/src/Schema/Page.php
index 3d546464..419dd2fd 100644
--- a/src/Schema/Page.php
+++ b/src/Schema/Page.php
@@ -12,14 +12,14 @@
 namespace Mcp\Schema;
 
 /**
- * @phpstan-type PageItem Tool|Prompt|ResourceTemplate|ResourceDefinition
+ * @template TItem of Tool|Prompt|ResourceTemplate|ResourceDefinition
  *
- * @extends \ArrayObject<int|string, PageItem>
+ * @extends \ArrayObject<int|string, TItem>
  */
 final class Page extends \ArrayObject
 {
     /**
-     * @param array<int|string, PageItem> $references Items can be Tool, Prompt, ResourceTemplate, or ResourceDefinition
+     * @param array<int|string, TItem> $references Items can be Tool, Prompt, ResourceTemplate, or ResourceDefinition
      */
     public function __construct(
         public readonly array $references,
diff --git a/src/Schema/Request/CallToolRequest.php b/src/Schema/Request/CallToolRequest.php
index 0674066c..29754663 100644
--- a/src/Schema/Request/CallToolRequest.php
+++ b/src/Schema/Request/CallToolRequest.php
@@ -59,7 +59,7 @@ protected static function fromParams(?array $params): static
     }
 
     /**
-     * @return array{name: string, arguments: array<string, mixed>}
+     * @return array{name: string, arguments: array<string, mixed>|\stdClass}
      */
     protected function getParams(): array
     {
diff --git a/src/Schema/Request/CompletionCompleteRequest.php b/src/Schema/Request/CompletionCompleteRequest.php
index 7ad0332c..ee362a21 100644
--- a/src/Schema/Request/CompletionCompleteRequest.php
+++ b/src/Schema/Request/CompletionCompleteRequest.php
@@ -45,8 +45,8 @@ protected static function fromParams(?array $params): static
         }
 
         $ref = match ($params['ref']['type'] ?? null) {
-            'ref/prompt' => new PromptReference(self::refString($params['ref'], 'name')),
-            'ref/resource' => new ResourceReference(self::refString($params['ref'], 'uri')),
+            'ref/prompt' => new PromptReference(self::stringMember($params['ref'], 'ref', 'name')),
+            'ref/resource' => new ResourceReference(self::stringMember($params['ref'], 'ref', 'uri')),
             default => throw new InvalidArgumentException('Invalid "ref" parameter for completion/complete.'),
         };
 
@@ -54,19 +54,22 @@ protected static function fromParams(?array $params): static
             throw new InvalidArgumentException('Missing or invalid "argument" parameter for completion/complete.');
         }
 
-        return new self($ref, $params['argument']);
+        return new self($ref, [
+            'name' => self::stringMember($params['argument'], 'argument', 'name'),
+            'value' => self::stringMember($params['argument'], 'argument', 'value'),
+        ]);
     }
 
     /**
-     * @param array<mixed> $ref
+     * @param array<mixed> $data
      */
-    private static function refString(array $ref, string $key): string
+    private static function stringMember(array $data, string $member, string $key): string
     {
-        if (!isset($ref[$key]) || !\is_string($ref[$key])) {
-            throw new InvalidArgumentException(\sprintf('Missing or invalid "ref.%s" parameter for completion/complete.', $key));
+        if (!isset($data[$key]) || !\is_string($data[$key])) {
+            throw new InvalidArgumentException(\sprintf('Missing or invalid "%s.%s" parameter for completion/complete.', $member, $key));
         }
 
-        return $ref[$key];
+        return $data[$key];
     }
 
     /**
diff --git a/src/Schema/Request/ElicitRequest.php b/src/Schema/Request/ElicitRequest.php
index 15a74ee1..ae540064 100644
--- a/src/Schema/Request/ElicitRequest.php
+++ b/src/Schema/Request/ElicitRequest.php
@@ -12,6 +12,7 @@
 namespace Mcp\Schema\Request;
 
 use Mcp\Exception\InvalidArgumentException;
+use Mcp\Exception\LogicException;
 use Mcp\Schema\Elicitation\ElicitationSchema;
 use Mcp\Schema\Enum\ElicitationMode;
 use Mcp\Schema\JsonRpc\Request;
@@ -110,6 +111,10 @@ protected static function fromParams(?array $params): static
     protected function getParams(): array
     {
         if (ElicitationMode::Url === $this->mode) {
+            if (null === $this->url) {
+                throw new LogicException('A url-mode elicitation has no "url" to send.');
+            }
+
             return [
                 'message' => $this->message,
                 'mode' => $this->mode->value,
@@ -117,6 +122,10 @@ protected function getParams(): array
             ];
         }
 
+        if (null === $this->requestedSchema) {
+            throw new LogicException('A form-mode elicitation has no "requestedSchema" to send.');
+        }
+
         // We don't need to send the mode if it's the default (form).
         return [
             'message' => $this->message,
diff --git a/src/Schema/ResourceDefinition.php b/src/Schema/ResourceDefinition.php
index 69c44d5f..1d2a1105 100644
--- a/src/Schema/ResourceDefinition.php
+++ b/src/Schema/ResourceDefinition.php
@@ -69,7 +69,7 @@ public function __construct(
     }
 
     /**
-     * @param ResourceDefinitionData $data
+     * @param ResourceDefinitionData|array<mixed> $data
      */
     public static function fromArray(array $data): self
     {
diff --git a/src/Schema/ResourceTemplate.php b/src/Schema/ResourceTemplate.php
index 46033975..2b7c6abb 100644
--- a/src/Schema/ResourceTemplate.php
+++ b/src/Schema/ResourceTemplate.php
@@ -62,7 +62,7 @@ public function __construct(
     }
 
     /**
-     * @param ResourceTemplateData $data
+     * @param ResourceTemplateData|array<mixed> $data
      */
     public static function fromArray(array $data): self
     {
diff --git a/src/Schema/Result/CallToolResult.php b/src/Schema/Result/CallToolResult.php
index b986becf..e2836a42 100644
--- a/src/Schema/Result/CallToolResult.php
+++ b/src/Schema/Result/CallToolResult.php
@@ -87,7 +87,7 @@ public static function error(array $content, ?array $meta = null): self
      *     isError?: bool,
      *     _meta?: array<string, mixed>,
      *     structuredContent?: mixed
-     * } $data
+     * }|array<mixed> $data
      */
     public static function fromArray(array $data): self
     {
diff --git a/src/Schema/Result/ElicitResult.php b/src/Schema/Result/ElicitResult.php
index 533d28f1..371ae4cd 100644
--- a/src/Schema/Result/ElicitResult.php
+++ b/src/Schema/Result/ElicitResult.php
@@ -42,7 +42,7 @@ public function __construct(
      * answers has to be passed in: it decides whether an accepted response is
      * expected to carry content.
      *
-     * @param array{action: string, content?: array<string, mixed>} $data
+     * @param array{action: string, content?: array<string, mixed>}|array<mixed> $data
      */
     public static function fromArray(array $data, ElicitationMode $mode = ElicitationMode::Form): self
     {
diff --git a/src/Schema/Result/InitializeResult.php b/src/Schema/Result/InitializeResult.php
index e80c28ca..39e036d3 100644
--- a/src/Schema/Result/InitializeResult.php
+++ b/src/Schema/Result/InitializeResult.php
@@ -50,7 +50,7 @@ public function __construct(
      *     serverInfo: array<string, mixed>,
      *     instructions?: string,
      *     _meta?: array<string, mixed>,
-     * } $data
+     * }|array<mixed> $data
      */
     public static function fromArray(array $data): self
     {
diff --git a/src/Schema/Result/ListRootsResult.php b/src/Schema/Result/ListRootsResult.php
index 613b53f6..9a6d2904 100644
--- a/src/Schema/Result/ListRootsResult.php
+++ b/src/Schema/Result/ListRootsResult.php
@@ -42,7 +42,7 @@ public function __construct(
      * @param array{
      *     roots: array<array{uri: string, name?: string}>,
      *     _meta?: ?array<string, mixed>
-     * } $data
+     * }|array<mixed> $data
      */
     public static function fromArray(array $data): self
     {
diff --git a/src/Schema/Root.php b/src/Schema/Root.php
index 97a2e3af..cad18f70 100644
--- a/src/Schema/Root.php
+++ b/src/Schema/Root.php
@@ -50,7 +50,7 @@ public function __construct(
     }
 
     /**
-     * @param RootData $data
+     * @param RootData|array<mixed> $data
      */
     public static function fromArray(array $data): self
     {
diff --git a/src/Schema/ServerCapabilities.php b/src/Schema/ServerCapabilities.php
index acc326c8..f398a458 100644
--- a/src/Schema/ServerCapabilities.php
+++ b/src/Schema/ServerCapabilities.php
@@ -146,14 +146,14 @@ public function withExtensions(array $extensions): self
 
     /**
      * @return array{
-     *     logging?: object,
-     *     completions?: object,
-     *     prompts?: object,
-     *     resources?: object,
-     *     tools?: object,
-     *     experimental?: object,
-     *     extensions?: object,
-     *     tasks?: object,
+     *     logging?: \stdClass,
+     *     completions?: \stdClass,
+     *     prompts?: \stdClass,
+     *     resources?: \stdClass,
+     *     tools?: \stdClass,
+     *     experimental?: \stdClass,
+     *     extensions?: \stdClass,
+     *     tasks?: \stdClass,
      * }
      */
     public function jsonSerialize(): array
@@ -217,7 +217,7 @@ public function jsonSerialize(): array
      *
      * @param array<string, mixed> $data
      */
-    private static function toObject(array $data): object
+    private static function toObject(array $data): \stdClass
     {
         return (object) array_map(
             static fn (mixed $value): mixed => \is_array($value) ? self::toObject($value) : $value,
diff --git a/src/Schema/Tool.php b/src/Schema/Tool.php
index 1f4d9cd1..97798834 100644
--- a/src/Schema/Tool.php
+++ b/src/Schema/Tool.php
@@ -23,16 +23,10 @@
  *
  * @phpstan-type ToolInputSchema array{
  *     type: 'object',
- *     properties: array<string, mixed>|\stdClass,
- *     required: string[]|null
- * }
- * @phpstan-type ToolOutputSchema array{
- *     type?: string,
- *     properties?: array<string, mixed>|\stdClass,
- *     required?: string[]|null,
- *     additionalProperties?: bool|array<string, mixed>|\stdClass,
- *     description?: string
+ *     properties?: array<mixed>|\stdClass,
+ *     required?: array<mixed>|null
  * }
+ * @phpstan-type ToolOutputSchema array<string, mixed>
  * @phpstan-type ToolData array{
  *     name: string,
  *     title?: string,
@@ -97,20 +91,20 @@ class Tool implements \JsonSerializable
     public readonly ?array $outputSchema;
 
     /**
-     * @param string                $name         the name of the tool
-     * @param ?string               $title        Optional human-readable title for display in UI
-     * @param ToolInputSchema       $inputSchema  a JSON Schema object (as a PHP array) defining the expected 'arguments' for the tool
-     * @param ?string               $description  A human-readable description of the tool.
-     *                                            This can be used by clients to improve the LLM's understanding of
-     *                                            available tools. It can be thought of like a "hint" to the model.
-     * @param ?ToolAnnotations      $annotations  optional additional tool information
-     * @param ?Icon[]               $icons        optional icons representing the tool
-     * @param ?array<string, mixed> $meta         Optional metadata
-     * @param ToolOutputSchema|null $outputSchema Optional JSON Schema (as a PHP array) describing the tool's
-     *                                            structuredContent. Unlike $inputSchema its root is unconstrained —
-     *                                            it may describe an array, a primitive, or a composition.
-     * @param ?ToolExecution        $execution    optional execution-related properties, such as whether the
-     *                                            tool can be called as a task
+     * @param string                    $name         the name of the tool
+     * @param ?string                   $title        Optional human-readable title for display in UI
+     * @param array<string, mixed>      $inputSchema  a JSON Schema object (as a PHP array) defining the expected 'arguments' for the tool
+     * @param ?string                   $description  A human-readable description of the tool.
+     *                                                This can be used by clients to improve the LLM's understanding of
+     *                                                available tools. It can be thought of like a "hint" to the model.
+     * @param ?ToolAnnotations          $annotations  optional additional tool information
+     * @param ?Icon[]                   $icons        optional icons representing the tool
+     * @param ?array<string, mixed>     $meta         Optional metadata
+     * @param array<string, mixed>|null $outputSchema Optional JSON Schema (as a PHP array) describing the tool's
+     *                                                structuredContent. Unlike $inputSchema its root is unconstrained —
+     *                                                it may describe an array, a primitive, or a composition.
+     * @param ?ToolExecution            $execution    optional execution-related properties, such as whether the
+     *                                                tool can be called as a task
      */
     public function __construct(
         public readonly string $name,
@@ -123,13 +117,9 @@ public function __construct(
         ?array $outputSchema = null,
         public readonly ?ToolExecution $execution = null,
     ) {
-        if (!isset($inputSchema['type']) || 'object' !== $inputSchema['type']) {
-            throw new InvalidArgumentException('Tool inputSchema must be a JSON Schema of type "object".');
-        }
-
         // Always normalize here so every construction path emits `{}` for empty
         // sub-schemas — not only SchemaGenerator / fromArray.
-        $this->inputSchema = self::normalizeSchema($inputSchema);
+        $this->inputSchema = self::normalizeInputSchema($inputSchema);
         $this->outputSchema = null !== $outputSchema ? self::normalizeSchema($outputSchema) : null;
 
         // An out-of-bounds `x-mcp-header` reachable through `properties` makes
@@ -142,7 +132,7 @@ public function __construct(
     }
 
     /**
-     * @param ToolData $data
+     * @param ToolData|array<mixed> $data
      */
     public static function fromArray(array $data): self
     {
@@ -216,6 +206,42 @@ public function jsonSerialize(): array
         return $data;
     }
 
+    /**
+     * Normalize an input schema and refuse members that are not what they claim.
+     *
+     * `fromArray()` feeds this untrusted wire data, so a member of the wrong
+     * type is rejected rather than replaced: quietly turning `properties: "x"`
+     * into `{}` would publish a tool contract nobody declared.
+     *
+     * @param array<string, mixed> $schema
+     *
+     * @return ToolInputSchema
+     */
+    private static function normalizeInputSchema(array $schema): array
+    {
+        $normalized = self::normalizeSchema($schema);
+
+        if (!isset($normalized['type']) || 'object' !== $normalized['type']) {
+            throw new InvalidArgumentException('Tool inputSchema must be a JSON Schema of type "object".');
+        }
+
+        if (\array_key_exists('properties', $normalized)
+            && !\is_array($normalized['properties'])
+            && !$normalized['properties'] instanceof \stdClass
+        ) {
+            throw new InvalidArgumentException('Tool inputSchema "properties" must be an object.');
+        }
+
+        if (\array_key_exists('required', $normalized)
+            && null !== $normalized['required']
+            && !\is_array($normalized['required'])
+        ) {
+            throw new InvalidArgumentException('Tool inputSchema "required" must be a list of property names.');
+        }
+
+        return $normalized;
+    }
+
     /**
      * Normalize a JSON Schema so that empty sub-schemas JSON-encode as `{}` rather than `[]`.
      *
diff --git a/src/Schema/ToolChoice.php b/src/Schema/ToolChoice.php
index ad003232..5c0f2bac 100644
--- a/src/Schema/ToolChoice.php
+++ b/src/Schema/ToolChoice.php
@@ -28,16 +28,19 @@ public function __construct(
     }
 
     /**
-     * @param array{mode?: string} $data
+     * @param array{mode?: string}|array<mixed> $data
      */
     public static function fromArray(array $data): self
     {
-        if (\array_key_exists('mode', $data) && !\is_string($data['mode'])) {
+        if (!\array_key_exists('mode', $data)) {
+            return new self(ToolChoiceMode::Auto);
+        }
+
+        if (!\is_string($data['mode'])) {
             throw new InvalidArgumentException('Invalid "mode" in ToolChoice data.');
         }
 
-        $mode = \array_key_exists('mode', $data) ? ToolChoiceMode::tryFrom($data['mode']) : ToolChoiceMode::Auto;
-        if (null === $mode) {
+        if (null === $mode = ToolChoiceMode::tryFrom($data['mode'])) {
             throw new InvalidArgumentException(\sprintf('Invalid tool choice mode "%s".', $data['mode']));
         }
 
diff --git a/src/Server/Builder.php b/src/Server/Builder.php
index f0fb238a..035074c9 100644
--- a/src/Server/Builder.php
+++ b/src/Server/Builder.php
@@ -242,9 +242,9 @@ final class Builder
     private array $discoveryExcludeDirs = [];
 
     /**
-     * @var string[]|null
+     * @var string[]
      */
-    private ?array $discoveryNamePatterns = null;
+    private array $discoveryNamePatterns = DiscovererInterface::DEFAULT_NAME_PATERNS;
 
     private ?ServerCapabilities $serverCapabilities = null;
 
diff --git a/src/Server/ClientGateway.php b/src/Server/ClientGateway.php
index a60e539c..d4452b15 100644
--- a/src/Server/ClientGateway.php
+++ b/src/Server/ClientGateway.php
@@ -157,12 +157,13 @@ public function sample(array|Content|string $message, int $maxTokens = 1000, int
         if (\is_string($message)) {
             $message = new TextContent($message);
         }
-        if (\is_object($message) && \in_array($message::class, [TextContent::class, AudioContent::class, ImageContent::class], true)) {
-            $message = [new SamplingMessage(Role::User, $message)];
-        }
+
+        $messages = $message instanceof TextContent || $message instanceof AudioContent || $message instanceof ImageContent
+            ? [new SamplingMessage(Role::User, $message)]
+            : $message;
 
         $request = new CreateSamplingMessageRequest(
-            messages: $message,
+            messages: $messages,
             maxTokens: $maxTokens,
             preferences: $preferences,
             systemPrompt: $options['systemPrompt'] ?? null,
diff --git a/src/Server/Protocol.php b/src/Server/Protocol.php
index df4a11c5..19e88852 100644
--- a/src/Server/Protocol.php
+++ b/src/Server/Protocol.php
@@ -250,7 +250,24 @@ private function handleInvalidMessage(TransportInterface $transport, InvalidInpu
      */
     private function dispatchEvent(object $event): object
     {
-        return $this->eventDispatcher?->dispatch($event) ?? $event;
+        if (null === $this->eventDispatcher) {
+            return $event;
+        }
+
+        $dispatched = $this->eventDispatcher->dispatch($event);
+
+        // PSR-14 dispatchers return the event they were given; a dispatcher that
+        // swaps it for something else is not what the caller asked to dispatch.
+        if (!$dispatched instanceof $event) {
+            $this->logger->debug('Event dispatcher returned a different object than it was given; keeping the original.', [
+                'event' => $event::class,
+                'returned' => $dispatched::class,
+            ]);
+
+            return $event;
+        }
+
+        return $dispatched;
     }
 
     /**
diff --git a/src/Server/Session/Session.php b/src/Server/Session/Session.php
index d49fefc1..24798cd4 100644
--- a/src/Server/Session/Session.php
+++ b/src/Server/Session/Session.php
@@ -66,18 +66,17 @@ public function get(string $key, mixed $default = null): mixed
     public function set(string $key, mixed $value, bool $overwrite = true): void
     {
         $segments = explode('.', $key);
+        $lastKey = array_pop($segments);
         $this->readData();
         $data = &$this->data;
 
-        while (\count($segments) > 1) {
-            $segment = array_shift($segments);
+        foreach ($segments as $segment) {
             if (!isset($data[$segment]) || !\is_array($data[$segment])) {
                 $data[$segment] = [];
             }
             $data = &$data[$segment];
         }
 
-        $lastKey = array_shift($segments);
         if ($overwrite || !isset($data[$lastKey])) {
             $data[$lastKey] = $value;
         }
@@ -104,18 +103,18 @@ public function has(string $key): bool
     public function forget(string $key): void
     {
         $segments = explode('.', $key);
+        $lastKey = array_pop($segments);
         $this->readData();
         $data = &$this->data;
 
-        while (\count($segments) > 1) {
-            $segment = array_shift($segments);
+        foreach ($segments as $segment) {
             if (!isset($data[$segment]) || !\is_array($data[$segment])) {
                 return;
             }
             $data = &$data[$segment];
         }
 
-        unset($data[array_shift($segments)]);
+        unset($data[$lastKey]);
     }
 
     public function clear(): void
diff --git a/src/Server/Stateless/StatelessProtocol.php b/src/Server/Stateless/StatelessProtocol.php
index 375469c8..4d6a8917 100644
--- a/src/Server/Stateless/StatelessProtocol.php
+++ b/src/Server/Stateless/StatelessProtocol.php
@@ -542,7 +542,24 @@ private function dispatch(string $method, array $decoded, RequestMeta $meta, str
      */
     private function dispatchEvent(object $event): object
     {
-        return $this->eventDispatcher?->dispatch($event) ?? $event;
+        if (null === $this->eventDispatcher) {
+            return $event;
+        }
+
+        $dispatched = $this->eventDispatcher->dispatch($event);
+
+        // PSR-14 dispatchers return the event they were given; a dispatcher that
+        // swaps it for something else is not what the caller asked to dispatch.
+        if (!$dispatched instanceof $event) {
+            $this->logger->debug('Event dispatcher returned a different object than it was given; keeping the original.', [
+                'event' => $event::class,
+                'returned' => $dispatched::class,
+            ]);
+
+            return $event;
+        }
+
+        return $dispatched;
     }
 
     /**
@@ -570,7 +587,7 @@ private function dispatchError(Error $error, Request $request, Session $session,
      * server genuinely does not implement it — but naming the extension turns
      * an opaque refusal into something the caller can act on.
      */
-    private function unknownMethod(string $method, string|int $id): Error
+    private function unknownMethod(string $method, string|int|null $id): Error
     {
         $extension = $this->extensionMethods[$method] ?? null;
 
diff --git a/src/Server/Subscription/PublishingEventDispatcher.php b/src/Server/Subscription/PublishingEventDispatcher.php
index a1c4e688..15016156 100644
--- a/src/Server/Subscription/PublishingEventDispatcher.php
+++ b/src/Server/Subscription/PublishingEventDispatcher.php
@@ -30,7 +30,7 @@
  */
 final class PublishingEventDispatcher implements EventDispatcherInterface
 {
-    /** @var array<class-string, callable(object): void> */
+    /** @var array<class-string, callable> */
     private readonly array $listeners;
 
     public function __construct(
diff --git a/src/Server/Subscription/RegistryChangePublisher.php b/src/Server/Subscription/RegistryChangePublisher.php
index f54a356d..363a2aea 100644
--- a/src/Server/Subscription/RegistryChangePublisher.php
+++ b/src/Server/Subscription/RegistryChangePublisher.php
@@ -67,7 +67,7 @@ public function onResourceTemplateListChanged(ResourceTemplateListChangedEvent $
      * Shaped for a dispatcher that wants a map; a framework's own subscriber
      * conventions can read it too rather than restating the list.
      *
-     * @return array<class-string, callable(object): void>
+     * @return array<class-string, callable>
      */
     public function listeners(): array
     {
diff --git a/src/Server/Transport/ManagesTransportCallbacks.php b/src/Server/Transport/ManagesTransportCallbacks.php
index eae14fa9..765e2ef3 100644
--- a/src/Server/Transport/ManagesTransportCallbacks.php
+++ b/src/Server/Transport/ManagesTransportCallbacks.php
@@ -39,7 +39,7 @@ trait ManagesTransportCallbacks
     /** @var callable(Uuid): array<int, array<string, mixed>> */
     protected $pendingRequestsProvider;
 
-    /** @var callable(int, Uuid): Response<array<string, mixed>>|Error|null */
+    /** @var (callable(int, Uuid): (Response<array<string, mixed>>|Error|null))|null */
     protected $responseFinder;
 
     /** @var callable(FiberSuspend|null, ?Uuid): void */
diff --git a/src/Server/Transport/StdioTransport.php b/src/Server/Transport/StdioTransport.php
index 565f7da7..92a49887 100644
--- a/src/Server/Transport/StdioTransport.php
+++ b/src/Server/Transport/StdioTransport.php
@@ -21,6 +21,8 @@
 /**
  * @extends BaseTransport<int>
  *
+ * @phpstan-import-type McpFiber from TransportInterface
+ *
  * @author Kyrian Obikwelu <koshnawaza@gmail.com>
  */
 class StdioTransport extends BaseTransport
@@ -33,6 +35,9 @@ class StdioTransport extends BaseTransport
     /** Whether the current over-length line is still being drained and discarded. */
     private bool $discardingLine = false;
 
+    /** @var positive-int */
+    private readonly int $maxLineBytes;
+
     /**
      * @param resource $input
      * @param resource $output
@@ -46,13 +51,15 @@ public function __construct(
         private $output = \STDOUT,
         ?LoggerInterface $logger = null,
         private readonly RunnerControlInterface $runnerControl = new RunnerControl(),
-        private readonly int $maxLineBytes = self::DEFAULT_MAX_LINE_BYTES,
+        int $maxLineBytes = self::DEFAULT_MAX_LINE_BYTES,
     ) {
         parent::__construct($logger);
 
         if ($maxLineBytes < 1) {
             throw new InvalidArgumentException(\sprintf('The maximum line size must be a positive number of bytes, got %d.', $maxLineBytes));
         }
+
+        $this->maxLineBytes = $maxLineBytes;
     }
 
     public function send(string $data, array $context): void
@@ -129,7 +136,7 @@ private function processFiber(): void
         }
 
         if ($this->sessionFiber->isTerminated()) {
-            $this->handleFiberTermination();
+            $this->handleFiberTermination($this->sessionFiber);
 
             return;
         }
@@ -171,9 +178,12 @@ private function processFiber(): void
         }
     }
 
-    private function handleFiberTermination(): void
+    /**
+     * @param McpFiber $fiber
+     */
+    private function handleFiberTermination(\Fiber $fiber): void
     {
-        $finalResult = $this->sessionFiber->getReturn();
+        $finalResult = $fiber->getReturn();
 
         if (null !== $finalResult) {
             try {
diff --git a/src/Server/Transport/StreamableHttpTransport.php b/src/Server/Transport/StreamableHttpTransport.php
index dcd408f7..f156d97a 100644
--- a/src/Server/Transport/StreamableHttpTransport.php
+++ b/src/Server/Transport/StreamableHttpTransport.php
@@ -50,6 +50,8 @@
  *
  * @extends BaseTransport<ResponseInterface>
  *
+ * @phpstan-import-type McpFiber from TransportInterface
+ *
  * @author Kyrian Obikwelu <koshnawaza@gmail.com>
  */
 class StreamableHttpTransport extends BaseTransport implements StatelessAwareTransportInterface
@@ -253,17 +255,23 @@ protected function createJsonResponse(): ResponseInterface
 
     protected function createStreamedResponse(): ResponseInterface
     {
-        $callback = function (): void {
+        $fiber = $this->sessionFiber;
+
+        $callback = function () use ($fiber): void {
+            if (null === $fiber) {
+                return;
+            }
+
             try {
                 $this->logger->info('SSE: Starting request processing loop');
 
-                while ($this->sessionFiber->isSuspended()) {
+                while ($fiber->isSuspended()) {
                     $this->flushOutgoingMessages($this->sessionId);
 
                     $pendingRequests = $this->getPendingRequests($this->sessionId);
 
                     if (empty($pendingRequests)) {
-                        $yielded = $this->sessionFiber->resume();
+                        $yielded = $fiber->resume();
                         $this->handleFiberYield($yielded, $this->sessionId);
                         continue;
                     }
@@ -277,7 +285,7 @@ protected function createStreamedResponse(): ResponseInterface
                         $response = $this->checkForResponse($requestId, $this->sessionId);
 
                         if (null !== $response) {
-                            $yielded = $this->sessionFiber->resume($response);
+                            $yielded = $fiber->resume($response);
                             $this->handleFiberYield($yielded, $this->sessionId);
                             $resumed = true;
                             break;
@@ -285,7 +293,7 @@ protected function createStreamedResponse(): ResponseInterface
 
                         if ($this->clock->now()->getTimestamp() - $timestamp >= $timeout) {
                             $error = Error::forInternalError('Request timed out', $requestId);
-                            $yielded = $this->sessionFiber->resume($error);
+                            $yielded = $fiber->resume($error);
                             $this->handleFiberYield($yielded, $this->sessionId);
                             $resumed = true;
                             break;
@@ -297,7 +305,7 @@ protected function createStreamedResponse(): ResponseInterface
                     } // Prevent tight loop
                 }
 
-                $this->handleFiberTermination();
+                $this->handleFiberTermination($fiber);
             } finally {
                 $this->sessionFiber = null;
             }
@@ -318,9 +326,12 @@ protected function createStreamedResponse(): ResponseInterface
         return $response;
     }
 
-    protected function handleFiberTermination(): void
+    /**
+     * @param McpFiber $fiber
+     */
+    protected function handleFiberTermination(\Fiber $fiber): void
     {
-        $finalResult = $this->sessionFiber->getReturn();
+        $finalResult = $fiber->getReturn();
 
         if (null !== $finalResult) {
             try {
diff --git a/src/Server/Wire/InboundClassifier.php b/src/Server/Wire/InboundClassifier.php
index 826284df..6956f495 100644
--- a/src/Server/Wire/InboundClassifier.php
+++ b/src/Server/Wire/InboundClassifier.php
@@ -175,7 +175,7 @@ private function classifyMessage(array $message, ?string $headerVersion): EraCla
             return self::eraOf($claim);
         }
 
-        if (!self::namesModern($headerVersion)) {
+        if (null === $headerVersion || !self::namesModern($headerVersion)) {
             return EraClassification::legacy();
         }
 
@@ -215,8 +215,8 @@ private static function eraOf(string $version): EraClassification
      * version this endpoint does not serve, and the handshake leg's version
      * middleware is what says so, naming everything the endpoint does serve.
      */
-    private static function namesModern(?string $version): bool
+    private static function namesModern(string $version): bool
     {
-        return null !== $version && true === ProtocolVersion::tryFrom($version)?->isModern();
+        return true === ProtocolVersion::tryFrom($version)?->isModern();
     }
 }
diff --git a/tests/Conformance/Elements.php b/tests/Conformance/Elements.php
index d7eac2b3..627c5ccb 100644
--- a/tests/Conformance/Elements.php
+++ b/tests/Conformance/Elements.php
@@ -200,7 +200,7 @@ public function resourceTemplate(string $id): TextResourceContents
                 'id' => $id,
                 'templateTest' => true,
                 'data' => \sprintf('Data for ID: %s', $id),
-            ]),
+            ], \JSON_THROW_ON_ERROR),
         );
     }
 
diff --git a/tests/Integration/CancellationTest.php b/tests/Integration/CancellationTest.php
index 434ee28c..1a9498b3 100644
--- a/tests/Integration/CancellationTest.php
+++ b/tests/Integration/CancellationTest.php
@@ -106,6 +106,16 @@ public function isCancellationRequested(): bool
      */
     private function events(string $log): array
     {
-        return array_map(static fn (string $line): array => json_decode($line, true, flags: \JSON_THROW_ON_ERROR), file($log, \FILE_IGNORE_NEW_LINES | \FILE_SKIP_EMPTY_LINES));
+        $lines = file($log, \FILE_IGNORE_NEW_LINES | \FILE_SKIP_EMPTY_LINES);
+        $this->assertNotFalse($lines);
+
+        $events = [];
+        foreach ($lines as $line) {
+            $event = json_decode($line, true, flags: \JSON_THROW_ON_ERROR);
+            $this->assertIsArray($event);
+            $events[] = $event;
+        }
+
+        return $events;
     }
 }
diff --git a/tests/Integration/Fixture/cancellation.php b/tests/Integration/Fixture/cancellation.php
index 249ac40b..a47beb4c 100644
--- a/tests/Integration/Fixture/cancellation.php
+++ b/tests/Integration/Fixture/cancellation.php
@@ -12,6 +12,10 @@
 // This fixture keeps a tool request pending while it reads the next JSON-RPC line.
 // The SDK server's single fiber cannot read cancellations during a blocking tool.
 $log = getenv('MCP_FIXTURE_LOG');
+if (false === $log) {
+    fwrite(\STDERR, "MCP_FIXTURE_LOG is not set.\n");
+    exit(1);
+}
 
 while (false !== ($line = fgets(\STDIN))) {
     $message = json_decode($line, true, flags: \JSON_THROW_ON_ERROR);
diff --git a/tests/Integration/HandshakeTest.php b/tests/Integration/HandshakeTest.php
index 99ff4647..7cca7c8f 100644
--- a/tests/Integration/HandshakeTest.php
+++ b/tests/Integration/HandshakeTest.php
@@ -76,8 +76,10 @@ public function testServerInfoIsExchanged(): void
     {
         $client = $this->connect('handshake');
 
-        $this->assertSame('integration-server', $client->getServerInfo()->name);
-        $this->assertSame('1.0.0', $client->getServerInfo()->version);
+        $serverInfo = $client->getServerInfo();
+        $this->assertNotNull($serverInfo);
+        $this->assertSame('integration-server', $serverInfo->name);
+        $this->assertSame('1.0.0', $serverInfo->version);
         $this->assertSame('Be brief.', $client->getInstructions());
         $this->assertTrue($client->isConnected());
     }
diff --git a/tests/Integration/SamplingTest.php b/tests/Integration/SamplingTest.php
index 0f452865..9de36bf7 100644
--- a/tests/Integration/SamplingTest.php
+++ b/tests/Integration/SamplingTest.php
@@ -51,9 +51,12 @@ public function testPromptReachesTheClient(): void
         $client->callTool('summarize', ['text' => 'inspect me']);
 
         $this->assertCount(1, $seen);
-        $this->assertInstanceOf(TextContent::class, $seen[0]->messages[0]->content);
-        $this->assertSame('inspect me', $seen[0]->messages[0]->content->text);
-        $this->assertSame(64, $seen[0]->maxTokens);
+
+        $request = $seen[0];
+        $this->assertInstanceOf(CreateSamplingMessageRequest::class, $request);
+        $this->assertInstanceOf(TextContent::class, $request->messages[0]->content);
+        $this->assertSame('inspect me', $request->messages[0]->content->text);
+        $this->assertSame(64, $request->maxTokens);
     }
 
     #[TestDox('a gateway parameter is injected, not published in the schema')]
@@ -69,9 +72,12 @@ public function testGatewayParameterIsInjectedNotPublished(): void
         }
 
         $this->assertNotNull($tool);
-        $this->assertArrayNotHasKey('client', $tool->inputSchema['properties']);
-        $this->assertArrayHasKey('text', $tool->inputSchema['properties']);
-        $this->assertSame(['text'], $tool->inputSchema['required']);
+
+        $properties = $tool->inputSchema['properties'] ?? null;
+        $this->assertIsArray($properties);
+        $this->assertArrayNotHasKey('client', $properties);
+        $this->assertArrayHasKey('text', $properties);
+        $this->assertSame(['text'], $tool->inputSchema['required'] ?? null);
 
         $result = $client->callTool('summarize_via_gateway', ['text' => 'a long report']);
 
diff --git a/tests/Integration/SamplingToolsTest.php b/tests/Integration/SamplingToolsTest.php
index 107f163b..58725346 100644
--- a/tests/Integration/SamplingToolsTest.php
+++ b/tests/Integration/SamplingToolsTest.php
@@ -51,12 +51,18 @@ public function testToolsReachTheClient(): void
         $client->callTool('weather_report', ['city' => 'Paris']);
 
         $this->assertCount(2, $seen);
-        $this->assertSame('get_weather', $seen[0]->tools[0]->name);
+
+        $first = $seen[0];
+        $this->assertInstanceOf(CreateSamplingMessageRequest::class, $first);
+        $this->assertNotNull($first->tools);
+        $this->assertSame('get_weather', $first->tools[0]->name);
 
         // Second turn carries the assistant's tool use and the server's tool result.
-        $this->assertCount(3, $seen[1]->messages);
-        $this->assertInstanceOf(ToolUseContent::class, $seen[1]->messages[1]->getContentBlocks()[0]);
-        $toolResult = $seen[1]->messages[2]->getContentBlocks()[0];
+        $second = $seen[1];
+        $this->assertInstanceOf(CreateSamplingMessageRequest::class, $second);
+        $this->assertCount(3, $second->messages);
+        $this->assertInstanceOf(ToolUseContent::class, $second->messages[1]->getContentBlocks()[0]);
+        $toolResult = $second->messages[2]->getContentBlocks()[0];
         $this->assertInstanceOf(ToolResultContent::class, $toolResult);
         $this->assertSame('call-1', $toolResult->toolUseId);
     }
diff --git a/tests/Interop/Client/EverythingServerTestCase.php b/tests/Interop/Client/EverythingServerTestCase.php
index 002fa4c0..8cc4d5e1 100644
--- a/tests/Interop/Client/EverythingServerTestCase.php
+++ b/tests/Interop/Client/EverythingServerTestCase.php
@@ -139,7 +139,7 @@ public function __invoke(ListRootsRequest $request): ListRootsResult
         self::$client->connect(self::$transport);
 
         foreach (self::$transport->received() as $message) {
-            if (isset($message->result->serverInfo)) {
+            if (isset($message->result->serverInfo) && $message->result instanceof \stdClass) {
                 self::$initializeResult = $message->result;
             }
         }
@@ -282,7 +282,7 @@ private function losses(array $wire, mixed $parsed, array $received): array
         }
 
         $losses = array_values(array_unique(array_map(
-            static fn (string $loss): string => preg_replace('/\.\d+(?=\.|$)/', '.*', $loss),
+            static fn (string $loss): string => preg_replace('/\.\d+(?=\.|$)/', '.*', $loss) ?? $loss,
             $losses,
         )));
         sort($losses);
@@ -411,6 +411,7 @@ private function assertMatchesSnapshot(string $scenario, mixed $data): void
 
         // The dynamic resources stamp the time they were generated into their text.
         $json = preg_replace('/\d{1,2}:\d{2}:\d{2}(?:\s?[AP]M)?/u', '<time>', $json);
+        $this->assertNotNull($json);
 
         $file = __DIR__.'/snapshots/'.$scenario.'.json';
 
diff --git a/tests/Interop/Server/Http/HttpSchemaShowcaseTest.php b/tests/Interop/Server/Http/HttpSchemaShowcaseTest.php
index bf2a7c87..32b0b70b 100644
--- a/tests/Interop/Server/Http/HttpSchemaShowcaseTest.php
+++ b/tests/Interop/Server/Http/HttpSchemaShowcaseTest.php
@@ -92,7 +92,7 @@ protected function getServerScript(): string
 
     protected function normalizeTestOutput(string $output, ?string $testName = null): string
     {
-        return match ($testName) {
+        $normalized = match ($testName) {
             'validate_profile' => preg_replace(
                 '/\d{4}-\d{2}-\d{2} \d{2}:\d{2}:\d{2}/',
                 '2025-01-01 00:00:00',
@@ -112,5 +112,7 @@ protected function normalizeTestOutput(string $output, ?string $testName = null)
             ], $output),
             default => $output,
         };
+
+        return $normalized ?? $output;
     }
 }
diff --git a/tests/Interop/Server/InspectorSnapshotTestCase.php b/tests/Interop/Server/InspectorSnapshotTestCase.php
index 97af0d7c..a4261fc3 100644
--- a/tests/Interop/Server/InspectorSnapshotTestCase.php
+++ b/tests/Interop/Server/InspectorSnapshotTestCase.php
@@ -105,6 +105,7 @@ public function testOutputMatchesSnapshot(
         }
 
         $expected = file_get_contents($snapshotFile);
+        $this->assertNotFalse($expected, \sprintf('Could not read snapshot "%s".', $snapshotFile));
 
         $message = \sprintf('Output does not match snapshot "%s".', $snapshotFile);
         $this->assertJsonStringEqualsJsonString($expected, $normalizedOutput, $message);
diff --git a/tests/Interop/Server/Stdio/StdioCustomDependenciesTest.php b/tests/Interop/Server/Stdio/StdioCustomDependenciesTest.php
index fc709d4b..4a167ffb 100644
--- a/tests/Interop/Server/Stdio/StdioCustomDependenciesTest.php
+++ b/tests/Interop/Server/Stdio/StdioCustomDependenciesTest.php
@@ -58,7 +58,7 @@ protected function getServerScript(): string
 
     protected function normalizeTestOutput(string $output, ?string $testName = null): string
     {
-        return match ($testName) {
+        $normalized = match ($testName) {
             'add_task' => preg_replace(
                 '/\d{4}-\d{2}-\d{2}T\d{2}:\d{2}:\d{2}[+-]\d{2}:\d{2}/',
                 '2025-01-01T00:00:00+00:00',
@@ -71,5 +71,7 @@ protected function normalizeTestOutput(string $output, ?string $testName = null)
             ),
             default => $output,
         };
+
+        return $normalized ?? $output;
     }
 }
diff --git a/tests/Unit/Capability/Completion/ListCompletionProviderTest.php b/tests/Unit/Capability/Completion/ListCompletionProviderTest.php
new file mode 100644
index 00000000..9a9ca9fc
--- /dev/null
+++ b/tests/Unit/Capability/Completion/ListCompletionProviderTest.php
@@ -0,0 +1,51 @@
+<?php
+
+/*
+ * This file is part of the official PHP MCP SDK.
+ *
+ * A collaboration between Symfony and the PHP Foundation.
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace Mcp\Tests\Unit\Capability\Completion;
+
+use Mcp\Capability\Completion\ListCompletionProvider;
+use PHPUnit\Framework\TestCase;
+
+final class ListCompletionProviderTest extends TestCase
+{
+    public function testCompletionsAreOfferedInFull(): void
+    {
+        $provider = new ListCompletionProvider(['draft', 'published', 'archived']);
+
+        $this->assertSame(['draft', 'published', 'archived'], $provider->getCompletions(''));
+    }
+
+    public function testCompletionsArePrefixMatched(): void
+    {
+        $provider = new ListCompletionProvider(['draft', 'published', 'archived']);
+
+        $this->assertSame(['draft'], $provider->getCompletions('dr'));
+    }
+
+    /**
+     * `#[CompletionProvider(values: ...)]` accepts ints and floats, but a
+     * completion goes on the wire as a string.
+     */
+    public function testNumericValuesBecomeStrings(): void
+    {
+        $provider = new ListCompletionProvider([101, 102.5, 'abc']);
+
+        $this->assertSame(['101', '102.5', 'abc'], $provider->getCompletions(''));
+        $this->assertSame(['101', '102.5'], $provider->getCompletions('10'));
+    }
+
+    public function testKeysAreDiscarded(): void
+    {
+        $provider = new ListCompletionProvider([5 => 'a', 9 => 'b']);
+
+        $this->assertSame(['a', 'b'], $provider->getCompletions(''));
+    }
+}
diff --git a/tests/Unit/Capability/Discovery/DiscoveryTest.php b/tests/Unit/Capability/Discovery/DiscoveryTest.php
index 628aaa6a..1e1fce0e 100644
--- a/tests/Unit/Capability/Discovery/DiscoveryTest.php
+++ b/tests/Unit/Capability/Discovery/DiscoveryTest.php
@@ -34,6 +34,20 @@ protected function setUp(): void
         $this->discoverer = new Discoverer();
     }
 
+    /**
+     * A file whose class PSR-4 cannot load is skipped, rather than handed on as
+     * a name that then fails inside `new ReflectionClass`.
+     */
+    public function testFileWithAnUnloadableClassIsSkipped(): void
+    {
+        $discovery = $this->discoverer->discover(__DIR__, ['UnloadableFixtures']);
+
+        $this->assertSame([], $discovery->getTools());
+        $this->assertSame([], $discovery->getPrompts());
+        $this->assertSame([], $discovery->getResources());
+        $this->assertSame([], $discovery->getResourceTemplates());
+    }
+
     public function testDiscoversAllElementTypesCorrectlyFromFixtureFiles(): void
     {
         $discovery = $this->discoverer->discover(__DIR__, ['Fixtures'], [], ['*.php', '*.inc']);
@@ -45,12 +59,17 @@ public function testDiscoversAllElementTypesCorrectlyFromFixtureFiles(): void
         $this->assertEquals('greet_user', $tools['greet_user']->tool->name);
         $this->assertEquals('Greets a user by name.', $tools['greet_user']->tool->description);
         $this->assertEquals([DiscoverableToolHandler::class, 'greet'], $tools['greet_user']->handler);
-        $this->assertArrayHasKey('name', $tools['greet_user']->tool->inputSchema['properties'] ?? []);
+        $greetProperties = $tools['greet_user']->tool->inputSchema['properties'] ?? [];
+        $this->assertIsArray($greetProperties);
+        $this->assertArrayHasKey('name', $greetProperties);
 
         $this->assertArrayHasKey('repeatAction', $tools);
         $this->assertEquals('A tool with more complex parameters and inferred name/description.', $tools['repeatAction']->tool->description);
+        $this->assertNotNull($tools['repeatAction']->tool->annotations);
         $this->assertTrue($tools['repeatAction']->tool->annotations->readOnlyHint);
-        $this->assertEquals(['count', 'loudly', 'mode'], array_keys($tools['repeatAction']->tool->inputSchema['properties'] ?? []));
+        $repeatProperties = $tools['repeatAction']->tool->inputSchema['properties'] ?? [];
+        $this->assertIsArray($repeatProperties);
+        $this->assertEquals(['count', 'loudly', 'mode'], array_keys($repeatProperties));
 
         $this->assertArrayHasKey('InvokableCalculator', $tools);
         $this->assertInstanceOf(ToolReference::class, $tools['InvokableCalculator']);
@@ -75,16 +94,17 @@ public function testDiscoversAllElementTypesCorrectlyFromFixtureFiles(): void
 
         $this->assertArrayHasKey('ui://widget/clock', $resources);
         $this->assertEquals(McpApps::MIME_TYPE, $resources['ui://widget/clock']->resource->mimeType);
-        $this->assertJsonStringEqualsJsonString('{"ui":{}}', json_encode($resources['ui://widget/clock']->resource->meta));
+        $this->assertJsonStringEqualsJsonString('{"ui":{}}', json_encode($resources['ui://widget/clock']->resource->meta, \JSON_THROW_ON_ERROR));
         $this->assertJsonStringEqualsJsonString(
             '{"ui":{"resourceUri":"ui://widget/clock","visibility":["app"]}}',
-            json_encode($tools['show_clock']->tool->meta),
+            json_encode($tools['show_clock']->tool->meta, \JSON_THROW_ON_ERROR),
         );
 
         $prompts = $discovery->getPrompts();
         $this->assertCount(4, $prompts);
 
         $this->assertArrayHasKey('creative_story_prompt', $prompts);
+        $this->assertNotNull($prompts['creative_story_prompt']->prompt->arguments);
         $this->assertCount(2, $prompts['creative_story_prompt']->prompt->arguments);
         $this->assertEquals(CompletionProviderFixture::class, $prompts['creative_story_prompt']->completionProviders['genre']);
 
diff --git a/tests/Unit/Capability/Discovery/DocBlockParserTest.php b/tests/Unit/Capability/Discovery/DocBlockParserTest.php
index a2a832ad..2bddb1bc 100644
--- a/tests/Unit/Capability/Discovery/DocBlockParserTest.php
+++ b/tests/Unit/Capability/Discovery/DocBlockParserTest.php
@@ -105,7 +105,9 @@ public function testGetTagsByNameReturnsSpecificTags(): void
         $deprecatedTags = $docBlock->getTagsByName('deprecated');
         $this->assertCount(1, $deprecatedTags);
         $this->assertInstanceOf(Deprecated::class, $deprecatedTags[0]);
-        $this->assertEquals('use newMethod() instead', $deprecatedTags[0]->getDescription()->render());
+        $deprecatedDescription = $deprecatedTags[0]->getDescription();
+        $this->assertNotNull($deprecatedDescription);
+        $this->assertEquals('use newMethod() instead', $deprecatedDescription->render());
 
         $seeTags = $docBlock->getTagsByName('see');
         $this->assertCount(1, $seeTags);
diff --git a/tests/Unit/Capability/Discovery/SchemaValidatorTest.php b/tests/Unit/Capability/Discovery/SchemaValidatorTest.php
index 739bc156..1028c97f 100644
--- a/tests/Unit/Capability/Discovery/SchemaValidatorTest.php
+++ b/tests/Unit/Capability/Discovery/SchemaValidatorTest.php
@@ -181,7 +181,7 @@ public function testArrayItemValidationErrorPointer(): void
     public function testValidatesDataPassedAsStdClassObject(): void
     {
         $schema = $this->getSimpleSchema();
-        $dataObj = json_decode(json_encode($this->getValidData())); // Convert to stdClass
+        $dataObj = json_decode(json_encode($this->getValidData(), \JSON_THROW_ON_ERROR)); // Convert to stdClass
 
         $errors = $this->validator->validateAgainstJsonSchema($dataObj, $schema);
         $this->assertEmpty($errors);
diff --git a/tests/Unit/Capability/Discovery/UnloadableFixtures/OrphanedHandler.php b/tests/Unit/Capability/Discovery/UnloadableFixtures/OrphanedHandler.php
new file mode 100644
index 00000000..81a8ea34
--- /dev/null
+++ b/tests/Unit/Capability/Discovery/UnloadableFixtures/OrphanedHandler.php
@@ -0,0 +1,29 @@
+<?php
+
+/*
+ * This file is part of the official PHP MCP SDK.
+ *
+ * A collaboration between Symfony and the PHP Foundation.
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+/*
+ * The namespace deliberately does not match this file's path, so PSR-4 cannot
+ * autoload the class and discovery has to skip the file. See
+ * {@see \Mcp\Tests\Unit\Capability\Discovery\DiscoveryTest}.
+ */
+
+namespace Mcp\Tests\Unit\Capability\Discovery\NotWhereThisFileLives;
+
+use Mcp\Capability\Attribute\McpTool;
+
+final class OrphanedHandler
+{
+    #[McpTool(name: 'orphaned_tool')]
+    public function orphaned(): string
+    {
+        return 'never discovered';
+    }
+}
diff --git a/tests/Unit/Capability/Formatter/PromptResultFormatterTest.php b/tests/Unit/Capability/Formatter/PromptResultFormatterTest.php
index 52bb1767..6a57c990 100644
--- a/tests/Unit/Capability/Formatter/PromptResultFormatterTest.php
+++ b/tests/Unit/Capability/Formatter/PromptResultFormatterTest.php
@@ -208,7 +208,9 @@ public function testFormatTypedTextResourceContentDefaultsMimeType(): void
             ],
         ]);
 
-        $this->assertSame('text/plain', $result[0]->content->resource->mimeType);
+        $content = $result[0]->content;
+        $this->assertInstanceOf(EmbeddedResource::class, $content);
+        $this->assertSame('text/plain', $content->resource->mimeType);
     }
 
     public function testFormatTypedBlobResourceContentDefaultsMimeType(): void
@@ -223,7 +225,9 @@ public function testFormatTypedBlobResourceContentDefaultsMimeType(): void
             ],
         ]);
 
-        $this->assertSame('application/octet-stream', $result[0]->content->resource->mimeType);
+        $content = $result[0]->content;
+        $this->assertInstanceOf(EmbeddedResource::class, $content);
+        $this->assertSame('application/octet-stream', $content->resource->mimeType);
     }
 
     public function testFormatTypedContentRejectsInvalidDataWithIndexContext(): void
diff --git a/tests/Unit/Capability/Registry/Loader/ChainLoaderTest.php b/tests/Unit/Capability/Registry/Loader/ChainLoaderTest.php
index 5488818e..e2c68d45 100644
--- a/tests/Unit/Capability/Registry/Loader/ChainLoaderTest.php
+++ b/tests/Unit/Capability/Registry/Loader/ChainLoaderTest.php
@@ -40,7 +40,9 @@ public function testLastWriterWinsForConflictingKeys(): void
 
         (new ChainLoader([$first, $second]))->load($registry);
 
-        $this->assertSame('second', ($registry->getTool('shared')->handler)());
+        $handler = $registry->getTool('shared')->handler;
+        $this->assertInstanceOf(\Closure::class, $handler);
+        $this->assertSame('second', $handler());
     }
 
     public function testEmptyChainIsNoop(): void
diff --git a/tests/Unit/Capability/Registry/Loader/DiscoveryLoaderTest.php b/tests/Unit/Capability/Registry/Loader/DiscoveryLoaderTest.php
index dcb1d8d4..25279a9f 100644
--- a/tests/Unit/Capability/Registry/Loader/DiscoveryLoaderTest.php
+++ b/tests/Unit/Capability/Registry/Loader/DiscoveryLoaderTest.php
@@ -81,7 +81,9 @@ public function testLoadTwiceUnregistersStaleAndKeepsNew(): void
 
         $updatedResource = $this->registry->getResource('r://1', false);
         $this->assertInstanceOf(ResourceReference::class, $updatedResource);
-        $this->assertSame('r1-updated', ($updatedResource->handler)());
+        $handler = $updatedResource->handler;
+        $this->assertInstanceOf(\Closure::class, $handler);
+        $this->assertSame('r1-updated', $handler());
 
         $this->expectException(ToolNotFoundException::class);
         $this->registry->getTool('t1');
@@ -150,7 +152,9 @@ public function testLoadOverwritesPreviousRegistrationOnSameKey(): void
         );
         $loader->load($this->registry);
 
-        $this->assertSame('v2', ($this->registry->getTool('t')->handler)());
+        $handler = $this->registry->getTool('t')->handler;
+        $this->assertInstanceOf(\Closure::class, $handler);
+        $this->assertSame('v2', $handler());
         $this->assertSame(['arg' => ListCompletionProvider::class], $this->registry->getPrompt('p')->completionProviders);
     }
 
@@ -166,7 +170,9 @@ public function testLoadPreservesConflictingRuntimeRegistration(): void
         ));
         (new DiscoveryLoader('/base', [], [], $discoverer))->load($this->registry);
 
-        $this->assertSame('runtime', ($this->registry->getTool('shared')->handler)());
+        $handler = $this->registry->getTool('shared')->handler;
+        $this->assertInstanceOf(\Closure::class, $handler);
+        $this->assertSame('runtime', $handler());
     }
 
     public function testLoadPreservesRuntimeOverrideOfPreviouslyOwnedEntry(): void
@@ -187,7 +193,9 @@ public function testLoadPreservesRuntimeOverrideOfPreviouslyOwnedEntry(): void
         );
         $loader->load($this->registry);
 
-        $this->assertSame('runtime', ($this->registry->getTool('shared')->handler)());
+        $handler = $this->registry->getTool('shared')->handler;
+        $this->assertInstanceOf(\Closure::class, $handler);
+        $this->assertSame('runtime', $handler());
     }
 
     public function testLoadDoesNotUnregisterRuntimeAdditions(): void
diff --git a/tests/Unit/Capability/Registry/Loader/ExplicitElementLoaderTest.php b/tests/Unit/Capability/Registry/Loader/ExplicitElementLoaderTest.php
index dad2de64..9403b1f4 100644
--- a/tests/Unit/Capability/Registry/Loader/ExplicitElementLoaderTest.php
+++ b/tests/Unit/Capability/Registry/Loader/ExplicitElementLoaderTest.php
@@ -14,6 +14,7 @@
 use Mcp\Capability\Completion\ProviderInterface;
 use Mcp\Capability\Registry;
 use Mcp\Capability\Registry\ReferenceHandler;
+use Mcp\Capability\Registry\ResourceReference;
 use Mcp\Capability\RegistryInterface;
 use Mcp\Exception\InvalidArgumentException;
 use Mcp\Schema\Prompt;
@@ -100,6 +101,7 @@ public function read(string $uri, ClientGateway $gateway): mixed
         $registry = $this->buildAndGetRegistry(static fn (Server\Builder $b) => $b->add($resource, $handler));
 
         $reference = $registry->getResource('config://demo', false);
+        $this->assertInstanceOf(ResourceReference::class, $reference);
         $this->assertSame('config://demo', $reference->resource->uri);
         $this->assertSame('demo', $reference->resource->name);
         $this->assertSame('text/plain', $reference->resource->mimeType);
diff --git a/tests/Unit/Capability/Registry/Loader/ReflectedElementLoaderResourceTitleTest.php b/tests/Unit/Capability/Registry/Loader/ReflectedElementLoaderResourceTitleTest.php
index 6dd09991..a8308a12 100644
--- a/tests/Unit/Capability/Registry/Loader/ReflectedElementLoaderResourceTitleTest.php
+++ b/tests/Unit/Capability/Registry/Loader/ReflectedElementLoaderResourceTitleTest.php
@@ -13,6 +13,7 @@
 
 use Mcp\Capability\Registry;
 use Mcp\Capability\Registry\Loader\ReflectedElementLoader;
+use Mcp\Capability\Registry\ResourceReference;
 use PHPUnit\Framework\TestCase;
 
 class ReflectedElementLoaderResourceTitleTest extends TestCase
@@ -40,6 +41,7 @@ public function testLoadPropagatesResourceTitleToRegisteredResource(): void
         $loader->load($registry);
 
         $resourceRef = $registry->getResource('config://app/settings');
+        $this->assertInstanceOf(ResourceReference::class, $resourceRef);
         $this->assertSame('Application Settings', $resourceRef->resource->title);
     }
 
diff --git a/tests/Unit/Capability/Registry/ReferenceHandlerTest.php b/tests/Unit/Capability/Registry/ReferenceHandlerTest.php
index 2952c811..ca2fa9fe 100644
--- a/tests/Unit/Capability/Registry/ReferenceHandlerTest.php
+++ b/tests/Unit/Capability/Registry/ReferenceHandlerTest.php
@@ -135,6 +135,33 @@ public function search(string $query, ClientGateway $gateway): string
         $this->assertInstanceOf(ClientGateway::class, $handler->receivedGateway);
     }
 
+    public function testHandleResolvesAClassStringAndMethodPairToAnInstance(): void
+    {
+        $session = $this->createMock(SessionInterface::class);
+        $session->method('getId')->willReturn(Uuid::v4());
+
+        $result = (new ReferenceHandler())->handle(new ElementReference([ArrayHandlerFixture::class, 'greet']), [
+            '_session' => $session,
+            '_request' => new \stdClass(),
+            'who' => 'bob',
+        ]);
+
+        $this->assertSame('hi bob', $result);
+    }
+
+    public function testHandleRefusesAnArrayHandlerWhoseMethodIsNotCallable(): void
+    {
+        $session = $this->createMock(SessionInterface::class);
+        $session->method('getId')->willReturn(Uuid::v4());
+
+        $this->expectException(InvalidArgumentException::class);
+
+        (new ReferenceHandler())->handle(new ElementReference([new ArrayHandlerFixture(), 'hidden']), [
+            '_session' => $session,
+            '_request' => new \stdClass(),
+        ]);
+    }
+
     public function testHandleStillReflectsOrdinaryClosuresAndDoesNotInjectArgumentBag(): void
     {
         $session = $this->createMock(SessionInterface::class);
@@ -264,3 +291,20 @@ public function testHandleIncludesParameterNameAndIndexWhenAVariadicElementFails
         ]);
     }
 }
+
+class ArrayHandlerFixture
+{
+    public function greet(string $who): string
+    {
+        return 'hi '.$who;
+    }
+
+    /**
+     * Not public, so `[$instance, 'hidden']` is not a callable and the handler
+     * has to refuse it rather than invoke it.
+     */
+    protected function hidden(): string
+    {
+        return 'unreachable';
+    }
+}
diff --git a/tests/Unit/Capability/RegistryTest.php b/tests/Unit/Capability/RegistryTest.php
index 118632a4..7bbf6a29 100644
--- a/tests/Unit/Capability/RegistryTest.php
+++ b/tests/Unit/Capability/RegistryTest.php
@@ -39,7 +39,7 @@
 class RegistryTest extends TestCase
 {
     private Registry $registry;
-    private LoggerInterface|MockObject $logger;
+    private LoggerInterface&MockObject $logger;
 
     protected function setUp(): void
     {
@@ -101,7 +101,9 @@ public function testRegisterToolOverwritesPriorRegistration(): void
         $this->registry->registerTool($second, static fn () => 'second');
 
         $toolRef = $this->registry->getTool('test_tool');
-        $this->assertEquals('second', ($toolRef->handler)());
+        $handler = $toolRef->handler;
+        $this->assertInstanceOf(\Closure::class, $handler);
+        $this->assertEquals('second', $handler());
     }
 
     public function testGetToolThrowsExceptionForUnregisteredTool(): void
@@ -158,7 +160,9 @@ public function testRegisterResourceOverwritesPriorRegistration(): void
         $this->registry->registerResource($second, static fn () => 'second');
 
         $resourceRef = $this->registry->getResource('test://resource');
-        $this->assertEquals('second', ($resourceRef->handler)());
+        $handler = $resourceRef->handler;
+        $this->assertInstanceOf(\Closure::class, $handler);
+        $this->assertEquals('second', $handler());
     }
 
     public function testGetResourceThrowsExceptionForUnregisteredResource(): void
@@ -268,7 +272,9 @@ public function testRegisterResourceTemplateOverwritesPriorRegistration(): void
         $this->registry->registerResourceTemplate($second, static fn () => 'second');
 
         $templateRef = $this->registry->getResourceTemplate('test://{id}');
-        $this->assertEquals('second', ($templateRef->handler)());
+        $handler = $templateRef->handler;
+        $this->assertInstanceOf(\Closure::class, $handler);
+        $this->assertEquals('second', $handler());
     }
 
     public function testResourceTemplateMatchingPrefersMoreSpecificMatches(): void
@@ -350,7 +356,9 @@ public function testRegisterPromptOverwritesPriorRegistration(): void
         $this->registry->registerPrompt($second, static fn () => 'second');
 
         $promptRef = $this->registry->getPrompt('test_prompt');
-        $this->assertEquals('second', ($promptRef->handler)());
+        $handler = $promptRef->handler;
+        $this->assertInstanceOf(\Closure::class, $handler);
+        $this->assertEquals('second', $handler());
     }
 
     public function testGetPromptThrowsExceptionForUnregisteredPrompt(): void
@@ -455,7 +463,9 @@ public function testMultipleRegistrationsOfSameElementWithSameType(): void
 
         // Second registration should override the first
         $toolRef = $this->registry->getTool('test_tool');
-        $this->assertEquals('second', ($toolRef->handler)());
+        $handler = $toolRef->handler;
+        $this->assertInstanceOf(\Closure::class, $handler);
+        $this->assertEquals('second', $handler());
     }
 
     public function testExtractStructuredContentReturnsNullWhenOutputSchemaIsNull(): void
@@ -508,7 +518,7 @@ public function testExtractStructuredContentKeepsAnEmptyObjectAsAnObject(): void
         $structuredContent = $this->registry->getTool('test_tool')->extractStructuredContent(new \stdClass());
 
         $this->assertInstanceOf(\stdClass::class, $structuredContent);
-        $this->assertStringContainsString('"structuredContent":{}', json_encode(new CallToolResult([], structuredContent: $structuredContent)));
+        $this->assertStringContainsString('"structuredContent":{}', json_encode(new CallToolResult([], structuredContent: $structuredContent), \JSON_THROW_ON_ERROR));
     }
 
     /**
diff --git a/tests/Unit/Client/Transport/HttpTransportListenTest.php b/tests/Unit/Client/Transport/HttpTransportListenTest.php
index 779a1e8e..85a06cf4 100644
--- a/tests/Unit/Client/Transport/HttpTransportListenTest.php
+++ b/tests/Unit/Client/Transport/HttpTransportListenTest.php
@@ -268,7 +268,7 @@ public function sendRequest(RequestInterface $request): ResponseInterface
                     'capabilities' => ['tools' => new \stdClass()],
                     'serverInfo' => ['name' => 'fake', 'version' => '1.0.0'],
                 ],
-            ]));
+            ], \JSON_THROW_ON_ERROR));
         }
 
         if ('server/discover' === ($message['method'] ?? null)) {
@@ -281,7 +281,7 @@ public function sendRequest(RequestInterface $request): ResponseInterface
                     'capabilities' => ['tools' => new \stdClass()],
                     'serverInfo' => ['name' => 'fake', 'version' => '1.0.0'],
                 ],
-            ]));
+            ], \JSON_THROW_ON_ERROR));
         }
 
         // Streamed, so the client reads its streams in the meantime: a JSON
@@ -326,7 +326,7 @@ private function socketPair(): array
             throw new \RuntimeException('Could not create a socket pair.');
         }
 
-        return $pair;
+        return [$pair[0], $pair[1]];
     }
 
     /**
diff --git a/tests/Unit/Client/Transport/HttpTransportTest.php b/tests/Unit/Client/Transport/HttpTransportTest.php
index c4f354b0..c18aac49 100644
--- a/tests/Unit/Client/Transport/HttpTransportTest.php
+++ b/tests/Unit/Client/Transport/HttpTransportTest.php
@@ -118,7 +118,7 @@ public function sendRequest(RequestInterface $request): ResponseInterface
                         'capabilities' => ['tools' => ['listChanged' => false]],
                         'serverInfo' => ['name' => 'test-server', 'version' => '1.0.0'],
                     ],
-                ]);
+                ], \JSON_THROW_ON_ERROR);
 
                 return new Response(200, [
                     'Content-Type' => 'application/json',
diff --git a/tests/Unit/Client/Transport/StdioTransportTest.php b/tests/Unit/Client/Transport/StdioTransportTest.php
index fb314083..ed7dc405 100644
--- a/tests/Unit/Client/Transport/StdioTransportTest.php
+++ b/tests/Unit/Client/Transport/StdioTransportTest.php
@@ -84,6 +84,7 @@ public function testRejectsNonPositiveCap(): void
     private function stream(string $contents)
     {
         $stream = fopen('php://temp', 'r+');
+        $this->assertNotFalse($stream);
         fwrite($stream, $contents);
         rewind($stream);
 
diff --git a/tests/Unit/ClientTest.php b/tests/Unit/ClientTest.php
index 558de954..3ecdb002 100644
--- a/tests/Unit/ClientTest.php
+++ b/tests/Unit/ClientTest.php
@@ -31,6 +31,17 @@ public function testBuilderReturnsBuilderInstance(): void
         $this->assertInstanceOf(Builder::class, Client::builder());
     }
 
+    #[TestDox('readResource() refuses an empty URI before it reaches the wire')]
+    public function testReadResourceRejectsAnEmptyUri(): void
+    {
+        $client = Client::builder()->build();
+
+        $this->expectException(InvalidArgumentException::class);
+        $this->expectExceptionMessage('Resource URI must not be empty.');
+
+        $client->readResource('');
+    }
+
     #[TestDox('connect() succeeds on the first attempt without retrying')]
     public function testConnectSucceedsWithoutRetrying(): void
     {
diff --git a/tests/Unit/Schema/ClientCapabilitiesTest.php b/tests/Unit/Schema/ClientCapabilitiesTest.php
index c2176e9f..2e9162ae 100644
--- a/tests/Unit/Schema/ClientCapabilitiesTest.php
+++ b/tests/Unit/Schema/ClientCapabilitiesTest.php
@@ -21,7 +21,7 @@ public function testSerializesRootsWithoutListChanged(): void
     {
         $capabilities = new ClientCapabilities(roots: true);
 
-        $data = json_decode(json_encode($capabilities), true);
+        $data = json_decode(json_encode($capabilities, \JSON_THROW_ON_ERROR), true);
 
         $this->assertArrayHasKey('roots', $data);
         $this->assertSame([], $data['roots']);
@@ -31,7 +31,7 @@ public function testSerializesRootsWithListChanged(): void
     {
         $capabilities = new ClientCapabilities(roots: true, rootsListChanged: true);
 
-        $data = json_decode(json_encode($capabilities), true);
+        $data = json_decode(json_encode($capabilities, \JSON_THROW_ON_ERROR), true);
 
         $this->assertSame(['listChanged' => true], $data['roots']);
     }
@@ -63,7 +63,7 @@ public function testRoundTripPreservesRootsListChanged(): void
     {
         $capabilities = new ClientCapabilities(roots: true, rootsListChanged: true);
 
-        $data = json_decode(json_encode($capabilities), true);
+        $data = json_decode(json_encode($capabilities, \JSON_THROW_ON_ERROR), true);
         $restored = ClientCapabilities::fromArray($data);
 
         $this->assertTrue($restored->roots);
@@ -75,10 +75,13 @@ public function testRoundTripPreservesSamplingSubCapabilities(): void
         $capabilities = new ClientCapabilities(sampling: true, samplingContext: true, samplingTools: true);
 
         $serialized = $capabilities->jsonSerialize();
-        $this->assertObjectHasProperty('context', $serialized['sampling']);
-        $this->assertObjectHasProperty('tools', $serialized['sampling']);
+        $this->assertIsArray($serialized);
+        $sampling = $serialized['sampling'] ?? null;
+        $this->assertIsObject($sampling);
+        $this->assertObjectHasProperty('context', $sampling);
+        $this->assertObjectHasProperty('tools', $sampling);
 
-        $restored = ClientCapabilities::fromArray(json_decode(json_encode($capabilities), true));
+        $restored = ClientCapabilities::fromArray(json_decode(json_encode($capabilities, \JSON_THROW_ON_ERROR), true));
 
         $this->assertTrue($restored->sampling);
         $this->assertTrue($restored->samplingContext);
@@ -90,10 +93,13 @@ public function testPlainSamplingLeavesSubCapabilitiesOff(): void
         $capabilities = new ClientCapabilities(sampling: true);
 
         $serialized = $capabilities->jsonSerialize();
-        $this->assertObjectNotHasProperty('context', $serialized['sampling']);
-        $this->assertObjectNotHasProperty('tools', $serialized['sampling']);
+        $this->assertIsArray($serialized);
+        $sampling = $serialized['sampling'] ?? null;
+        $this->assertIsObject($sampling);
+        $this->assertObjectNotHasProperty('context', $sampling);
+        $this->assertObjectNotHasProperty('tools', $sampling);
 
-        $restored = ClientCapabilities::fromArray(json_decode(json_encode($capabilities), true));
+        $restored = ClientCapabilities::fromArray(json_decode(json_encode($capabilities, \JSON_THROW_ON_ERROR), true));
 
         $this->assertTrue($restored->sampling);
         $this->assertFalse($restored->samplingContext);
diff --git a/tests/Unit/Schema/Content/ImageContentTest.php b/tests/Unit/Schema/Content/ImageContentTest.php
index b1672021..da5c214c 100644
--- a/tests/Unit/Schema/Content/ImageContentTest.php
+++ b/tests/Unit/Schema/Content/ImageContentTest.php
@@ -61,14 +61,14 @@ public function testJsonSerializeIncludesAnnotations(): void
 
         $data = $content->jsonSerialize();
 
-        $this->assertSame($annotations, $data['annotations']);
+        $this->assertSame($annotations, $data['annotations'] ?? null);
     }
 
     public function testRoundTripWithAnnotations(): void
     {
         $original = new ImageContent(base64_encode('binary'), 'image/png', new Annotations([Role::User], 0.5));
 
-        $decoded = json_decode(json_encode($original), true);
+        $decoded = json_decode(json_encode($original, \JSON_THROW_ON_ERROR), true);
         $rehydrated = ImageContent::fromArray($decoded);
 
         $this->assertSame($original->data, $rehydrated->data);
diff --git a/tests/Unit/Schema/Content/PromptMessageTest.php b/tests/Unit/Schema/Content/PromptMessageTest.php
index 8808d412..46a41657 100644
--- a/tests/Unit/Schema/Content/PromptMessageTest.php
+++ b/tests/Unit/Schema/Content/PromptMessageTest.php
@@ -47,14 +47,14 @@ public function testJsonSerializeIncludesResourceLinkContent(): void
                 'uri' => 'file:///a.png',
                 'name' => 'a.png',
             ],
-        ], json_decode(json_encode($message), true));
+        ], json_decode(json_encode($message, \JSON_THROW_ON_ERROR), true));
     }
 
     public function testRoundTripWithResourceLink(): void
     {
         $original = new PromptMessage(Role::User, new ResourceLink('file:///a.png', 'a.png', mimeType: 'image/png'));
 
-        $decoded = json_decode(json_encode($original), true);
+        $decoded = json_decode(json_encode($original, \JSON_THROW_ON_ERROR), true);
         $rehydrated = PromptMessage::fromArray($decoded);
 
         $this->assertSame(Role::User, $rehydrated->role);
@@ -67,7 +67,6 @@ public function testFromArrayRejectsUnknownContentType(): void
     {
         $this->expectException(InvalidArgumentException::class);
 
-        /* @phpstan-ignore argument.type */
         PromptMessage::fromArray([
             'role' => 'user',
             'content' => ['type' => 'not-a-real-type'],
diff --git a/tests/Unit/Schema/Content/ResourceLinkTest.php b/tests/Unit/Schema/Content/ResourceLinkTest.php
index ca064558..4283a808 100644
--- a/tests/Unit/Schema/Content/ResourceLinkTest.php
+++ b/tests/Unit/Schema/Content/ResourceLinkTest.php
@@ -100,13 +100,13 @@ public function testJsonSerializeWithAllFields(): void
         $this->assertSame('resource_link', $data['type']);
         $this->assertSame(self::VALID_URI, $data['uri']);
         $this->assertSame('main.rs', $data['name']);
-        $this->assertSame('Main Source File', $data['title']);
-        $this->assertSame('Primary application entry point', $data['description']);
-        $this->assertSame('text/x-rust', $data['mimeType']);
-        $this->assertSame($annotations, $data['annotations']);
-        $this->assertSame(1024, $data['size']);
-        $this->assertSame($icons, $data['icons']);
-        $this->assertSame(['origin' => 'test'], $data['_meta']);
+        $this->assertSame('Main Source File', $data['title'] ?? null);
+        $this->assertSame('Primary application entry point', $data['description'] ?? null);
+        $this->assertSame('text/x-rust', $data['mimeType'] ?? null);
+        $this->assertSame($annotations, $data['annotations'] ?? null);
+        $this->assertSame(1024, $data['size'] ?? null);
+        $this->assertSame($icons, $data['icons'] ?? null);
+        $this->assertSame(['origin' => 'test'], $data['_meta'] ?? null);
     }
 
     public function testOptionalFieldsOmittedWhenNull(): void
@@ -159,8 +159,9 @@ public function testFromArrayWithAllFields(): void
         $this->assertSame('text/x-rust', $link->mimeType);
         $this->assertInstanceOf(Annotations::class, $link->annotations);
         $this->assertSame(1024, $link->size);
+        $this->assertNotNull($link->icons);
         $this->assertCount(1, $link->icons);
-        $this->assertInstanceOf(Icon::class, $link->icons[0]);
+        $this->assertInstanceOf(Icon::class, $link->icons[0] ?? null);
         $this->assertSame(['origin' => 'test'], $link->meta);
     }
 
@@ -178,7 +179,7 @@ public function testRoundTripThroughJsonSerializeAndFromArray(): void
             meta: ['origin' => 'test'],
         );
 
-        $decoded = json_decode(json_encode($original), true);
+        $decoded = json_decode(json_encode($original, \JSON_THROW_ON_ERROR), true);
         $rehydrated = ResourceLink::fromArray($decoded);
 
         $this->assertSame($original->uri, $rehydrated->uri);
@@ -196,7 +197,6 @@ public function testFromArrayRejectsWrongType(): void
         $this->expectException(InvalidArgumentException::class);
         $this->expectExceptionMessage('Invalid type for ResourceLink.');
 
-        /* @phpstan-ignore argument.type */
         ResourceLink::fromArray([
             'type' => 'resource',
             'uri' => self::VALID_URI,
diff --git a/tests/Unit/Schema/Content/SamplingMessageTest.php b/tests/Unit/Schema/Content/SamplingMessageTest.php
index c464575b..e3e1b2e3 100644
--- a/tests/Unit/Schema/Content/SamplingMessageTest.php
+++ b/tests/Unit/Schema/Content/SamplingMessageTest.php
@@ -41,14 +41,15 @@ public function testToolLoopMessagesRoundTrip(): void
             ]],
         ]);
 
-        $this->assertInstanceOf(ToolUseContent::class, $assistant->content[1]);
+        $this->assertInstanceOf(ToolUseContent::class, $assistant->getContentBlocks()[1]);
         $this->assertSame(['provider' => 'test'], $assistant->meta);
-        $this->assertSame(['provider' => 'test'], $assistant->jsonSerialize()['_meta']);
-        $this->assertInstanceOf(ToolResultContent::class, $user->content[0]);
-        $this->assertSame(['temperature' => 21], $user->content[0]->structuredContent);
+        $this->assertSame(['provider' => 'test'], $assistant->jsonSerialize()['_meta'] ?? null);
+        $toolResult = $user->getContentBlocks()[0];
+        $this->assertInstanceOf(ToolResultContent::class, $toolResult);
+        $this->assertSame(['temperature' => 21], $toolResult->structuredContent);
 
-        $this->assertEquals($assistant, SamplingMessage::fromArray(json_decode(json_encode($assistant), true)));
-        $this->assertEquals($user, SamplingMessage::fromArray(json_decode(json_encode($user), true)));
+        $this->assertEquals($assistant, SamplingMessage::fromArray(json_decode(json_encode($assistant, \JSON_THROW_ON_ERROR), true)));
+        $this->assertEquals($user, SamplingMessage::fromArray(json_decode(json_encode($user, \JSON_THROW_ON_ERROR), true)));
     }
 
     public function testSingleContentBlockKeepsItsShape(): void
@@ -119,7 +120,6 @@ public function testUnknownRoleIsRejected(): void
     {
         $this->expectException(InvalidArgumentException::class);
 
-        /* @phpstan-ignore argument.type */
         SamplingMessage::fromArray(['role' => 'system', 'content' => ['type' => 'text', 'text' => 'hi']]);
     }
 }
diff --git a/tests/Unit/Schema/Content/ToolResultContentTest.php b/tests/Unit/Schema/Content/ToolResultContentTest.php
index 3c45f664..51348730 100644
--- a/tests/Unit/Schema/Content/ToolResultContentTest.php
+++ b/tests/Unit/Schema/Content/ToolResultContentTest.php
@@ -43,7 +43,7 @@ public function testRoundTrip(): void
         $this->assertInstanceOf(TextContent::class, $textContent);
         $this->assertSame('21 C', $textContent->text);
 
-        $restored = ToolResultContent::fromArray(json_decode(json_encode($content), true));
+        $restored = ToolResultContent::fromArray(json_decode(json_encode($content, \JSON_THROW_ON_ERROR), true));
         $this->assertEquals($content, $restored);
     }
 
@@ -56,7 +56,7 @@ public function testIsErrorIsOmittedWhenFalse(): void
         $this->assertArrayNotHasKey('isError', $serialized);
         $this->assertArrayNotHasKey('structuredContent', $serialized);
         $this->assertArrayNotHasKey('_meta', $serialized);
-        $this->assertFalse(ToolResultContent::fromArray(json_decode(json_encode($content), true))->isError);
+        $this->assertFalse(ToolResultContent::fromArray(json_decode(json_encode($content, \JSON_THROW_ON_ERROR), true))->isError);
     }
 
     public function testAcceptsEveryCallToolResultContentBlock(): void
diff --git a/tests/Unit/Schema/Content/ToolUseContentTest.php b/tests/Unit/Schema/Content/ToolUseContentTest.php
index 686481ba..f40d36c7 100644
--- a/tests/Unit/Schema/Content/ToolUseContentTest.php
+++ b/tests/Unit/Schema/Content/ToolUseContentTest.php
@@ -49,7 +49,7 @@ public function testEmptyInputSerializesAsObject(): void
 
     public function testEmptyInputSurvivesRoundTrip(): void
     {
-        $decoded = json_decode(json_encode(new ToolUseContent('call-1', 'ping', [])), true);
+        $decoded = json_decode(json_encode(new ToolUseContent('call-1', 'ping', []), \JSON_THROW_ON_ERROR), true);
 
         $this->assertSame([], ToolUseContent::fromArray($decoded)->input);
     }
diff --git a/tests/Unit/Schema/Elicitation/BooleanSchemaDefinitionTest.php b/tests/Unit/Schema/Elicitation/BooleanSchemaDefinitionTest.php
index a9e11732..71aa4d99 100644
--- a/tests/Unit/Schema/Elicitation/BooleanSchemaDefinitionTest.php
+++ b/tests/Unit/Schema/Elicitation/BooleanSchemaDefinitionTest.php
@@ -86,7 +86,6 @@ public function testFromArrayRejectsNonStringTitle(): void
         $this->expectException(InvalidArgumentException::class);
         $this->expectExceptionMessage('Invalid "title" for boolean schema definition.');
 
-        /* @phpstan-ignore argument.type */
         BooleanSchemaDefinition::fromArray(['title' => 42]);
     }
 
diff --git a/tests/Unit/Schema/Elicitation/ElicitationSchemaTest.php b/tests/Unit/Schema/Elicitation/ElicitationSchemaTest.php
index d085f302..5ee2fec5 100644
--- a/tests/Unit/Schema/Elicitation/ElicitationSchemaTest.php
+++ b/tests/Unit/Schema/Elicitation/ElicitationSchemaTest.php
@@ -180,7 +180,6 @@ public function testFromArrayWithMissingProperties(): void
         $this->expectException(InvalidArgumentException::class);
         $this->expectExceptionMessage('Missing or invalid "properties"');
 
-        /* @phpstan-ignore argument.type */
         ElicitationSchema::fromArray([]);
     }
 
@@ -219,7 +218,6 @@ public function testFromArrayWithMissingPropertyType(): void
         $this->expectException(InvalidArgumentException::class);
         $this->expectExceptionMessage('Missing or invalid "type"');
 
-        /* @phpstan-ignore argument.type */
         ElicitationSchema::fromArray([
             'properties' => [
                 'name' => ['title' => 'Name'],
@@ -335,7 +333,7 @@ public function testJsonSerializeWithRequiredFields(): void
 
         $result = $schema->jsonSerialize();
 
-        $this->assertSame(['name'], $result['required']);
+        $this->assertSame(['name'], $result['required'] ?? null);
     }
 
     public function testJsonSerializeWithFullSchema(): void
@@ -353,7 +351,7 @@ public function testJsonSerializeWithFullSchema(): void
 
         $this->assertSame('object', $result['type']);
         $this->assertCount(3, $result['properties']);
-        $this->assertSame(['name', 'age'], $result['required']);
+        $this->assertSame(['name', 'age'], $result['required'] ?? null);
 
         $this->assertSame('string', $result['properties']['name']['type']);
         $this->assertSame('Full Name', $result['properties']['name']['title']);
diff --git a/tests/Unit/Schema/Elicitation/EnumSchemaDefinitionTest.php b/tests/Unit/Schema/Elicitation/EnumSchemaDefinitionTest.php
index ea200a86..2ae7046d 100644
--- a/tests/Unit/Schema/Elicitation/EnumSchemaDefinitionTest.php
+++ b/tests/Unit/Schema/Elicitation/EnumSchemaDefinitionTest.php
@@ -129,7 +129,6 @@ public function testFromArrayRejectsNonStringTitle(): void
         $this->expectException(InvalidArgumentException::class);
         $this->expectExceptionMessage('Invalid "title" for enum schema definition.');
 
-        /* @phpstan-ignore argument.type */
         EnumSchemaDefinition::fromArray(['title' => 42]);
     }
 
@@ -138,7 +137,6 @@ public function testFromArrayWithMissingEnum(): void
         $this->expectException(InvalidArgumentException::class);
         $this->expectExceptionMessage('Missing or invalid "enum"');
 
-        /* @phpstan-ignore argument.type */
         EnumSchemaDefinition::fromArray(['title' => 'Test']);
     }
 
diff --git a/tests/Unit/Schema/Elicitation/MultiSelectEnumSchemaDefinitionTest.php b/tests/Unit/Schema/Elicitation/MultiSelectEnumSchemaDefinitionTest.php
index 208f5d2c..a36de82f 100644
--- a/tests/Unit/Schema/Elicitation/MultiSelectEnumSchemaDefinitionTest.php
+++ b/tests/Unit/Schema/Elicitation/MultiSelectEnumSchemaDefinitionTest.php
@@ -154,7 +154,6 @@ public function testFromArrayRejectsNonStringTitle(): void
         $this->expectException(InvalidArgumentException::class);
         $this->expectExceptionMessage('Invalid "title" for multi-select enum schema definition.');
 
-        /* @phpstan-ignore argument.type */
         MultiSelectEnumSchemaDefinition::fromArray([
             'title' => 42,
             'items' => ['type' => 'string', 'enum' => ['a']],
@@ -166,7 +165,6 @@ public function testFromArrayWithMissingItemsEnum(): void
         $this->expectException(InvalidArgumentException::class);
         $this->expectExceptionMessage('Missing or invalid "items.enum"');
 
-        /* @phpstan-ignore argument.type */
         MultiSelectEnumSchemaDefinition::fromArray([
             'title' => 'Test',
             'items' => ['type' => 'string'],
diff --git a/tests/Unit/Schema/Elicitation/NumberSchemaDefinitionTest.php b/tests/Unit/Schema/Elicitation/NumberSchemaDefinitionTest.php
index ea040382..6398da5c 100644
--- a/tests/Unit/Schema/Elicitation/NumberSchemaDefinitionTest.php
+++ b/tests/Unit/Schema/Elicitation/NumberSchemaDefinitionTest.php
@@ -148,7 +148,6 @@ public function testFromArrayRejectsNonStringTitle(): void
         $this->expectException(InvalidArgumentException::class);
         $this->expectExceptionMessage('Invalid "title" for number schema definition.');
 
-        /* @phpstan-ignore argument.type */
         NumberSchemaDefinition::fromArray(['title' => 42]);
     }
 
diff --git a/tests/Unit/Schema/Elicitation/StringSchemaDefinitionTest.php b/tests/Unit/Schema/Elicitation/StringSchemaDefinitionTest.php
index 02998cce..524f458a 100644
--- a/tests/Unit/Schema/Elicitation/StringSchemaDefinitionTest.php
+++ b/tests/Unit/Schema/Elicitation/StringSchemaDefinitionTest.php
@@ -129,7 +129,6 @@ public function testFromArrayRejectsNonStringTitle(): void
         $this->expectException(InvalidArgumentException::class);
         $this->expectExceptionMessage('Invalid "title" for string schema definition.');
 
-        /* @phpstan-ignore argument.type */
         StringSchemaDefinition::fromArray(['title' => 42]);
     }
 
diff --git a/tests/Unit/Schema/Elicitation/TitledEnumSchemaDefinitionTest.php b/tests/Unit/Schema/Elicitation/TitledEnumSchemaDefinitionTest.php
index 26502832..f7f3347e 100644
--- a/tests/Unit/Schema/Elicitation/TitledEnumSchemaDefinitionTest.php
+++ b/tests/Unit/Schema/Elicitation/TitledEnumSchemaDefinitionTest.php
@@ -63,7 +63,6 @@ public function testConstructorWithMissingConst(): void
         $this->expectException(InvalidArgumentException::class);
         $this->expectExceptionMessage('Each oneOf item must have a string "const" property');
 
-        /* @phpstan-ignore argument.type */
         new TitledEnumSchemaDefinition('Test', [['title' => 'A']]);
     }
 
@@ -72,7 +71,6 @@ public function testConstructorWithMissingTitle(): void
         $this->expectException(InvalidArgumentException::class);
         $this->expectExceptionMessage('Each oneOf item must have a string "title" property');
 
-        /* @phpstan-ignore argument.type */
         new TitledEnumSchemaDefinition('Test', [['const' => 'a']]);
     }
 
@@ -139,7 +137,6 @@ public function testFromArrayRejectsNonStringTitle(): void
         $this->expectException(InvalidArgumentException::class);
         $this->expectExceptionMessage('Invalid "title" for titled enum schema definition.');
 
-        /* @phpstan-ignore argument.type */
         TitledEnumSchemaDefinition::fromArray(['title' => 42]);
     }
 
@@ -148,7 +145,6 @@ public function testFromArrayWithMissingOneOf(): void
         $this->expectException(InvalidArgumentException::class);
         $this->expectExceptionMessage('Missing or invalid "oneOf"');
 
-        /* @phpstan-ignore argument.type */
         TitledEnumSchemaDefinition::fromArray(['title' => 'Test']);
     }
 
diff --git a/tests/Unit/Schema/Elicitation/TitledMultiSelectEnumSchemaDefinitionTest.php b/tests/Unit/Schema/Elicitation/TitledMultiSelectEnumSchemaDefinitionTest.php
index 170893fb..6bf1853c 100644
--- a/tests/Unit/Schema/Elicitation/TitledMultiSelectEnumSchemaDefinitionTest.php
+++ b/tests/Unit/Schema/Elicitation/TitledMultiSelectEnumSchemaDefinitionTest.php
@@ -70,7 +70,6 @@ public function testConstructorWithMissingConst(): void
         $this->expectException(InvalidArgumentException::class);
         $this->expectExceptionMessage('Each anyOf item must have a string "const" property');
 
-        /* @phpstan-ignore argument.type */
         new TitledMultiSelectEnumSchemaDefinition('Test', [['title' => 'A']]);
     }
 
@@ -79,7 +78,6 @@ public function testConstructorWithMissingTitle(): void
         $this->expectException(InvalidArgumentException::class);
         $this->expectExceptionMessage('Each anyOf item must have a string "title" property');
 
-        /* @phpstan-ignore argument.type */
         new TitledMultiSelectEnumSchemaDefinition('Test', [['const' => 'a']]);
     }
 
@@ -183,7 +181,6 @@ public function testFromArrayRejectsNonStringTitle(): void
         $this->expectException(InvalidArgumentException::class);
         $this->expectExceptionMessage('Invalid "title" for titled multi-select enum schema definition.');
 
-        /* @phpstan-ignore argument.type */
         TitledMultiSelectEnumSchemaDefinition::fromArray([
             'title' => 42,
             'items' => ['anyOf' => [['const' => 'a', 'title' => 'A']]],
@@ -195,7 +192,6 @@ public function testFromArrayWithMissingItemsAnyOf(): void
         $this->expectException(InvalidArgumentException::class);
         $this->expectExceptionMessage('Missing or invalid "items.anyOf"');
 
-        /* @phpstan-ignore argument.type */
         TitledMultiSelectEnumSchemaDefinition::fromArray([
             'title' => 'Test',
             'items' => [],
diff --git a/tests/Unit/Schema/Extension/Apps/McpAppsTest.php b/tests/Unit/Schema/Extension/Apps/McpAppsTest.php
index 6e2f60a0..30b8074f 100644
--- a/tests/Unit/Schema/Extension/Apps/McpAppsTest.php
+++ b/tests/Unit/Schema/Extension/Apps/McpAppsTest.php
@@ -42,10 +42,10 @@ public function testUiResourceCspSerialization(): void
 
         $serialized = $csp->jsonSerialize();
 
-        $this->assertSame(['https://api.example.com'], $serialized['connectDomains']);
-        $this->assertSame(['https://cdn.example.com'], $serialized['resourceDomains']);
-        $this->assertSame(['https://embed.example.com'], $serialized['frameDomains']);
-        $this->assertSame(['https://example.com'], $serialized['baseUriDomains']);
+        $this->assertSame(['https://api.example.com'], $serialized['connectDomains'] ?? null);
+        $this->assertSame(['https://cdn.example.com'], $serialized['resourceDomains'] ?? null);
+        $this->assertSame(['https://embed.example.com'], $serialized['frameDomains'] ?? null);
+        $this->assertSame(['https://example.com'], $serialized['baseUriDomains'] ?? null);
     }
 
     public function testUiResourceCspOmitsNullFields(): void
@@ -142,8 +142,8 @@ public function testUiResourceContentMetaSerialization(): void
 
         $this->assertArrayHasKey('csp', $serialized);
         $this->assertArrayHasKey('permissions', $serialized);
-        $this->assertSame('example.com', $serialized['domain']);
-        $this->assertTrue($serialized['prefersBorder']);
+        $this->assertSame('example.com', $serialized['domain'] ?? null);
+        $this->assertTrue($serialized['prefersBorder'] ?? null);
     }
 
     public function testUiResourceContentMetaOmitsNullFields(): void
@@ -184,8 +184,8 @@ public function testUiToolMetaSerialization(): void
 
         $serialized = $meta->jsonSerialize();
 
-        $this->assertSame('ui://my-app', $serialized['resourceUri']);
-        $this->assertSame(['model', 'app'], $serialized['visibility']);
+        $this->assertSame('ui://my-app', $serialized['resourceUri'] ?? null);
+        $this->assertSame(['model', 'app'], $serialized['visibility'] ?? null);
     }
 
     public function testUiToolMetaOmitsNullFields(): void
diff --git a/tests/Unit/Schema/Extension/CapabilitiesExtensionsTest.php b/tests/Unit/Schema/Extension/CapabilitiesExtensionsTest.php
index dbb7e7e2..b118f50b 100644
--- a/tests/Unit/Schema/Extension/CapabilitiesExtensionsTest.php
+++ b/tests/Unit/Schema/Extension/CapabilitiesExtensionsTest.php
@@ -54,7 +54,9 @@ public function testServerCapabilitiesJsonSerializeWithExtensions(): void
         $json = $caps->jsonSerialize();
 
         $this->assertArrayHasKey('extensions', $json);
-        $this->assertObjectHasProperty(McpApps::EXTENSION_ID, $json['extensions']);
+        $extensions = $json['extensions'] ?? null;
+        $this->assertNotNull($extensions);
+        $this->assertObjectHasProperty(McpApps::EXTENSION_ID, $extensions);
     }
 
     public function testServerCapabilitiesSerializeSettinglessExtensionAsObject(): void
@@ -125,7 +127,7 @@ public function testServerCapabilitiesWithExtensionsMerges(): void
 
         $merged = $caps->withExtensions(['b' => ['y' => 99], 'c' => ['z' => 3]]);
 
-        $this->assertSame(['x' => 1], $merged->extensions['a']);
+        $this->assertSame(['x' => 1], $merged->extensions['a'] ?? null);
         $this->assertSame(['y' => 99], $merged->extensions['b'], 'new entry overrides existing id');
         $this->assertSame(['z' => 3], $merged->extensions['c']);
         $this->assertSame(['a' => ['x' => 1], 'b' => ['y' => 2]], $caps->extensions, 'original is unchanged');
@@ -171,9 +173,12 @@ public function testClientCapabilitiesJsonSerializeWithExtensions(): void
         );
 
         $json = $caps->jsonSerialize();
+        $this->assertIsArray($json);
 
         $this->assertArrayHasKey('extensions', $json);
-        $this->assertObjectHasProperty(McpApps::EXTENSION_ID, $json['extensions']);
+        $extensions = $json['extensions'] ?? null;
+        $this->assertNotNull($extensions);
+        $this->assertObjectHasProperty(McpApps::EXTENSION_ID, $extensions);
     }
 
     public function testClientCapabilitiesJsonSerializeWithoutExtensions(): void
@@ -256,6 +261,7 @@ public function testBackwardCompatibilityClientCapabilities(): void
         $this->assertNull($caps->extensions);
 
         $json = $caps->jsonSerialize();
+        $this->assertIsArray($json);
         $this->assertArrayNotHasKey('extensions', $json);
     }
 }
diff --git a/tests/Unit/Schema/IconTest.php b/tests/Unit/Schema/IconTest.php
index 65e00e24..4f7f1537 100644
--- a/tests/Unit/Schema/IconTest.php
+++ b/tests/Unit/Schema/IconTest.php
@@ -24,13 +24,14 @@ public function testValidConstructor(): void
 
         $this->assertSame('https://www.php.net/images/logos/php-logo-white.svg', $icon->src);
         $this->assertSame('image/svg+xml', $icon->mimeType);
-        $this->assertSame('any', $icon->sizes[0]);
+        $this->assertSame('any', $icon->sizes[0] ?? null);
     }
 
     public function testConstructorWithMultipleSizes(): void
     {
         $icon = new Icon('https://example.com/icon.png', 'image/png', ['48x48', '96x96']);
 
+        $this->assertNotNull($icon->sizes);
         $this->assertCount(2, $icon->sizes);
         $this->assertSame(['48x48', '96x96'], $icon->sizes);
     }
@@ -92,7 +93,7 @@ public function testFromArrayReadsTheme(): void
         $icon = Icon::fromArray(['src' => 'https://example.com/icon.png', 'theme' => 'dark']);
 
         $this->assertSame(IconTheme::Dark, $icon->theme);
-        $this->assertSame('dark', $icon->jsonSerialize()['theme']);
+        $this->assertSame('dark', $icon->jsonSerialize()['theme'] ?? null);
     }
 
     public function testFromArrayRejectsUnknownTheme(): void
diff --git a/tests/Unit/Schema/ImplementationTest.php b/tests/Unit/Schema/ImplementationTest.php
index 3268b6b1..0da76c4a 100644
--- a/tests/Unit/Schema/ImplementationTest.php
+++ b/tests/Unit/Schema/ImplementationTest.php
@@ -93,7 +93,6 @@ public function testFromArrayThrowsOnMissingName(): void
         $this->expectException(InvalidArgumentException::class);
         $this->expectExceptionMessage('Invalid or missing "name" in Implementation data.');
 
-        /* @phpstan-ignore argument.type */
         Implementation::fromArray(['version' => '1.0.0']);
     }
 
@@ -110,7 +109,6 @@ public function testFromArrayThrowsOnNonStringName(): void
         $this->expectException(InvalidArgumentException::class);
         $this->expectExceptionMessage('Invalid or missing "name" in Implementation data.');
 
-        /* @phpstan-ignore argument.type */
         Implementation::fromArray(['name' => 123, 'version' => '1.0.0']);
     }
 
@@ -119,7 +117,6 @@ public function testFromArrayThrowsOnMissingVersion(): void
         $this->expectException(InvalidArgumentException::class);
         $this->expectExceptionMessage('Invalid or missing "version" in Implementation data.');
 
-        /* @phpstan-ignore argument.type */
         Implementation::fromArray(['name' => 'my-client']);
     }
 
@@ -136,7 +133,6 @@ public function testFromArrayThrowsOnNonStringVersion(): void
         $this->expectException(InvalidArgumentException::class);
         $this->expectExceptionMessage('Invalid or missing "version" in Implementation data.');
 
-        /* @phpstan-ignore argument.type */
         Implementation::fromArray(['name' => 'my-client', 'version' => 1]);
     }
 
@@ -145,7 +141,6 @@ public function testFromArrayThrowsOnNonArrayIcons(): void
         $this->expectException(InvalidArgumentException::class);
         $this->expectExceptionMessage('Invalid "icons" in Implementation data; expected an array.');
 
-        /* @phpstan-ignore argument.type */
         Implementation::fromArray(['name' => 'my-client', 'version' => '1.0.0', 'icons' => 'nope']);
     }
 
@@ -154,7 +149,6 @@ public function testFromArrayThrowsOnNonStringDescription(): void
         $this->expectException(InvalidArgumentException::class);
         $this->expectExceptionMessage('Invalid "description" in Implementation data.');
 
-        /* @phpstan-ignore argument.type */
         Implementation::fromArray(['name' => 'my-client', 'version' => '1.0.0', 'description' => 42]);
     }
 
@@ -163,7 +157,6 @@ public function testFromArrayThrowsOnNonStringTitle(): void
         $this->expectException(InvalidArgumentException::class);
         $this->expectExceptionMessage('Invalid "title" in Implementation data.');
 
-        /* @phpstan-ignore argument.type */
         Implementation::fromArray(['name' => 'my-client', 'version' => '1.0.0', 'title' => ['nope']]);
     }
 
diff --git a/tests/Unit/Schema/NonObjectOutputSchemaTest.php b/tests/Unit/Schema/NonObjectOutputSchemaTest.php
index 8e0fb0ba..c84420ef 100644
--- a/tests/Unit/Schema/NonObjectOutputSchemaTest.php
+++ b/tests/Unit/Schema/NonObjectOutputSchemaTest.php
@@ -70,7 +70,6 @@ public function testInputSchemaStillRequiresObjectRoot(): void
     {
         $this->expectException(InvalidArgumentException::class);
 
-        /* @phpstan-ignore-next-line argument.type (deliberately invalid: an array root must be rejected) */
         Tool::fromArray([
             'name' => 'demo',
             'inputSchema' => ['type' => 'array', 'properties' => [], 'required' => null],
@@ -117,7 +116,7 @@ public function testNonNullValueIsSerialized(mixed $value): void
         $serialized = $result->jsonSerialize();
 
         $this->assertArrayHasKey('structuredContent', $serialized);
-        $this->assertSame($value, $serialized['structuredContent']);
+        $this->assertSame($value, $serialized['structuredContent'] ?? null);
     }
 
     #[TestDox('a null structuredContent is omitted entirely')]
@@ -149,7 +148,7 @@ public function testObjectRoundTrip(): void
         ]);
 
         $this->assertSame(['temperature' => 22.5], $result->structuredContent);
-        $this->assertSame(['temperature' => 22.5], $result->jsonSerialize()['structuredContent']);
+        $this->assertSame(['temperature' => 22.5], $result->jsonSerialize()['structuredContent'] ?? null);
     }
 
     #[TestDox('the empty root schema serializes as {} rather than []')]
@@ -161,6 +160,6 @@ public function testEmptyOutputSchemaSerializesAsObject(): void
             'outputSchema' => [],
         ]);
 
-        $this->assertSame('{}', json_encode($tool->jsonSerialize()['outputSchema']));
+        $this->assertSame('{}', json_encode($tool->jsonSerialize()['outputSchema'] ?? null));
     }
 }
diff --git a/tests/Unit/Schema/Request/CompletionCompleteRequestTest.php b/tests/Unit/Schema/Request/CompletionCompleteRequestTest.php
new file mode 100644
index 00000000..6aaf0144
--- /dev/null
+++ b/tests/Unit/Schema/Request/CompletionCompleteRequestTest.php
@@ -0,0 +1,133 @@
+<?php
+
+/*
+ * This file is part of the official PHP MCP SDK.
+ *
+ * A collaboration between Symfony and the PHP Foundation.
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace Mcp\Tests\Unit\Schema\Request;
+
+use Mcp\Exception\InvalidArgumentException;
+use Mcp\Schema\PromptReference;
+use Mcp\Schema\Request\CompletionCompleteRequest;
+use Mcp\Schema\ResourceReference;
+use PHPUnit\Framework\Attributes\DataProvider;
+use PHPUnit\Framework\TestCase;
+
+final class CompletionCompleteRequestTest extends TestCase
+{
+    public function testFromArrayReadsAPromptReference(): void
+    {
+        $request = self::fromParams([
+            'ref' => ['type' => 'ref/prompt', 'name' => 'book_seat'],
+            'argument' => ['name' => 'seat', 'value' => '12'],
+        ]);
+
+        $this->assertInstanceOf(PromptReference::class, $request->ref);
+        $this->assertSame('book_seat', $request->ref->name);
+        $this->assertSame(['name' => 'seat', 'value' => '12'], $request->argument);
+    }
+
+    public function testFromArrayReadsAResourceReference(): void
+    {
+        $request = self::fromParams([
+            'ref' => ['type' => 'ref/resource', 'uri' => 'user://{userId}/profile'],
+            'argument' => ['name' => 'userId', 'value' => '10'],
+        ]);
+
+        $this->assertInstanceOf(ResourceReference::class, $request->ref);
+        $this->assertSame('user://{userId}/profile', $request->ref->uri);
+    }
+
+    /**
+     * An empty value is the client asking what every completion is, which is a
+     * question worth answering — unlike a value that is not there at all.
+     */
+    public function testEmptyArgumentValueIsAccepted(): void
+    {
+        $request = self::fromParams([
+            'ref' => ['type' => 'ref/prompt', 'name' => 'book_seat'],
+            'argument' => ['name' => 'seat', 'value' => ''],
+        ]);
+
+        $this->assertSame(['name' => 'seat', 'value' => ''], $request->argument);
+    }
+
+    /**
+     * @param array<string, mixed> $params
+     */
+    #[DataProvider('provideMalformedParams')]
+    public function testMalformedParamsAreRejected(array $params, string $expectedMessage): void
+    {
+        $this->expectException(InvalidArgumentException::class);
+        $this->expectExceptionMessage($expectedMessage);
+
+        self::fromParams($params);
+    }
+
+    /**
+     * @return iterable<string, array{array<string, mixed>, string}>
+     */
+    public static function provideMalformedParams(): iterable
+    {
+        $ref = ['type' => 'ref/prompt', 'name' => 'book_seat'];
+        $argument = ['name' => 'seat', 'value' => '12'];
+
+        yield 'missing ref' => [
+            ['argument' => $argument],
+            'Missing or invalid "ref" parameter for completion/complete.',
+        ];
+
+        yield 'unknown ref type' => [
+            ['ref' => ['type' => 'ref/nothing'], 'argument' => $argument],
+            'Invalid "ref" parameter for completion/complete.',
+        ];
+
+        yield 'prompt ref without a name' => [
+            ['ref' => ['type' => 'ref/prompt'], 'argument' => $argument],
+            'Missing or invalid "ref.name" parameter for completion/complete.',
+        ];
+
+        yield 'resource ref without a uri' => [
+            ['ref' => ['type' => 'ref/resource'], 'argument' => $argument],
+            'Missing or invalid "ref.uri" parameter for completion/complete.',
+        ];
+
+        yield 'missing argument' => [
+            ['ref' => $ref],
+            'Missing or invalid "argument" parameter for completion/complete.',
+        ];
+
+        yield 'argument without a name' => [
+            ['ref' => $ref, 'argument' => ['value' => '12']],
+            'Missing or invalid "argument.name" parameter for completion/complete.',
+        ];
+
+        yield 'argument without a value' => [
+            ['ref' => $ref, 'argument' => ['name' => 'seat']],
+            'Missing or invalid "argument.value" parameter for completion/complete.',
+        ];
+
+        yield 'argument value that is not a string' => [
+            ['ref' => $ref, 'argument' => ['name' => 'seat', 'value' => 12]],
+            'Missing or invalid "argument.value" parameter for completion/complete.',
+        ];
+    }
+
+    /**
+     * @param array<string, mixed> $params
+     */
+    private static function fromParams(array $params): CompletionCompleteRequest
+    {
+        return CompletionCompleteRequest::fromArray([
+            'jsonrpc' => '2.0',
+            'id' => 1,
+            'method' => 'completion/complete',
+            'params' => $params,
+        ]);
+    }
+}
diff --git a/tests/Unit/Schema/Request/CreateSamplingMessageRequestTest.php b/tests/Unit/Schema/Request/CreateSamplingMessageRequestTest.php
index fb065e61..ddc22717 100644
--- a/tests/Unit/Schema/Request/CreateSamplingMessageRequestTest.php
+++ b/tests/Unit/Schema/Request/CreateSamplingMessageRequestTest.php
@@ -65,11 +65,15 @@ public function testToolsAndToolChoiceRoundTrip(): void
         );
 
         $payload = $request->withId(1)->jsonSerialize();
-        $this->assertSame('weather', $payload['params']['tools'][0]->name);
-        $this->assertSame(ToolChoiceMode::Required, $payload['params']['toolChoice']->mode);
+        $params = $payload['params'] ?? null;
+        $this->assertIsArray($params);
+        $this->assertSame('weather', $params['tools'][0]->name);
+        $this->assertSame(ToolChoiceMode::Required, $params['toolChoice']->mode);
 
         $hydrated = CreateSamplingMessageRequest::fromArray(json_decode(json_encode($payload, \JSON_THROW_ON_ERROR), true, flags: \JSON_THROW_ON_ERROR));
+        $this->assertNotNull($hydrated->tools);
         $this->assertSame('weather', $hydrated->tools[0]->name);
+        $this->assertNotNull($hydrated->toolChoice);
         $this->assertSame(ToolChoiceMode::Required, $hydrated->toolChoice->mode);
     }
 
diff --git a/tests/Unit/Schema/ResourceDefinitionTest.php b/tests/Unit/Schema/ResourceDefinitionTest.php
index e6bbe56a..65241c89 100644
--- a/tests/Unit/Schema/ResourceDefinitionTest.php
+++ b/tests/Unit/Schema/ResourceDefinitionTest.php
@@ -102,7 +102,7 @@ public function testTitleSerialization(): void
         );
 
         $data = $resource->jsonSerialize();
-        $this->assertSame('Book Listing', $data['title']);
+        $this->assertSame('Book Listing', $data['title'] ?? null);
     }
 
     public function testTitleOmittedWhenNull(): void
diff --git a/tests/Unit/Schema/ResourceTemplateTest.php b/tests/Unit/Schema/ResourceTemplateTest.php
index b99c9d08..70adde4d 100644
--- a/tests/Unit/Schema/ResourceTemplateTest.php
+++ b/tests/Unit/Schema/ResourceTemplateTest.php
@@ -100,7 +100,7 @@ public function testTitleSerialization(): void
         );
 
         $data = $resource->jsonSerialize();
-        $this->assertSame('Book Listing', $data['title']);
+        $this->assertSame('Book Listing', $data['title'] ?? null);
     }
 
     public function testTitleOmittedWhenNull(): void
diff --git a/tests/Unit/Schema/Result/CallToolResultTest.php b/tests/Unit/Schema/Result/CallToolResultTest.php
index f7c2b6ff..42095d0c 100644
--- a/tests/Unit/Schema/Result/CallToolResultTest.php
+++ b/tests/Unit/Schema/Result/CallToolResultTest.php
@@ -95,7 +95,7 @@ public function testRoundTripWithResourceLinkAlongsideOtherContentTypes(): void
             EmbeddedResource::fromText('file:///readme.txt', 'hello'),
         ]);
 
-        $decoded = json_decode(json_encode($original), true);
+        $decoded = json_decode(json_encode($original, \JSON_THROW_ON_ERROR), true);
         $rehydrated = CallToolResult::fromArray($decoded);
 
         $this->assertCount(5, $rehydrated->content);
diff --git a/tests/Unit/Schema/Result/CreateSamplingMessageResultTest.php b/tests/Unit/Schema/Result/CreateSamplingMessageResultTest.php
index 41961058..a65f6b6b 100644
--- a/tests/Unit/Schema/Result/CreateSamplingMessageResultTest.php
+++ b/tests/Unit/Schema/Result/CreateSamplingMessageResultTest.php
@@ -33,11 +33,11 @@ public function testArrayContentAndKnownStopReasonAreHydrated(): void
             '_meta' => ['traceId' => 'trace-1'],
         ]);
 
-        $this->assertInstanceOf(TextContent::class, $result->content[0]);
-        $this->assertInstanceOf(ToolUseContent::class, $result->content[1]);
+        $this->assertInstanceOf(TextContent::class, $result->getContentBlocks()[0]);
+        $this->assertInstanceOf(ToolUseContent::class, $result->getContentBlocks()[1]);
         $this->assertSame('toolUse', $result->stopReason);
-        $this->assertSame('toolUse', $result->jsonSerialize()['stopReason']);
-        $this->assertSame(['traceId' => 'trace-1'], $result->jsonSerialize()['_meta']);
+        $this->assertSame('toolUse', $result->jsonSerialize()['stopReason'] ?? null);
+        $this->assertSame(['traceId' => 'trace-1'], $result->jsonSerialize()['_meta'] ?? null);
     }
 
     public function testProviderSpecificStopReasonIsPreserved(): void
@@ -50,7 +50,7 @@ public function testProviderSpecificStopReasonIsPreserved(): void
         ]);
 
         $this->assertSame('provider-specific', $result->stopReason);
-        $this->assertSame('provider-specific', $result->jsonSerialize()['stopReason']);
+        $this->assertSame('provider-specific', $result->jsonSerialize()['stopReason'] ?? null);
     }
 
     public function testKnownStopReasonStaysAString(): void
diff --git a/tests/Unit/Schema/Result/ElicitResultTest.php b/tests/Unit/Schema/Result/ElicitResultTest.php
index b946c770..574203a0 100644
--- a/tests/Unit/Schema/Result/ElicitResultTest.php
+++ b/tests/Unit/Schema/Result/ElicitResultTest.php
@@ -80,7 +80,6 @@ public function testFromArrayWithMissingAction(): void
         $this->expectException(InvalidArgumentException::class);
         $this->expectExceptionMessage('Missing or invalid "action"');
 
-        /* @phpstan-ignore argument.type */
         ElicitResult::fromArray([]);
     }
 
diff --git a/tests/Unit/Schema/Result/ListRootsResultTest.php b/tests/Unit/Schema/Result/ListRootsResultTest.php
index 46729fbf..c3cfaf10 100644
--- a/tests/Unit/Schema/Result/ListRootsResultTest.php
+++ b/tests/Unit/Schema/Result/ListRootsResultTest.php
@@ -59,7 +59,6 @@ public function testFromArrayWithMissingRoots(): void
         $this->expectException(InvalidArgumentException::class);
         $this->expectExceptionMessage('Missing or invalid "roots"');
 
-        /* @phpstan-ignore argument.type */
         ListRootsResult::fromArray([]);
     }
 
@@ -68,7 +67,6 @@ public function testFromArrayWithNonArrayRoot(): void
         $this->expectException(InvalidArgumentException::class);
         $this->expectExceptionMessage('Invalid root in ListRootsResult data, expected an array.');
 
-        /* @phpstan-ignore argument.type */
         ListRootsResult::fromArray([
             'roots' => ['file:///tmp'],
         ]);
@@ -96,7 +94,7 @@ public function testFromArrayRoundTrip(): void
 
         $result = ListRootsResult::fromArray($data);
 
-        $this->assertSame($data, json_decode(json_encode($result), true));
+        $this->assertSame($data, json_decode(json_encode($result, \JSON_THROW_ON_ERROR), true));
     }
 
     public function testJsonSerializeWithoutMeta(): void
@@ -105,6 +103,6 @@ public function testJsonSerializeWithoutMeta(): void
 
         $this->assertSame([
             'roots' => [['uri' => 'file:///tmp']],
-        ], json_decode(json_encode($result), true));
+        ], json_decode(json_encode($result, \JSON_THROW_ON_ERROR), true));
     }
 }
diff --git a/tests/Unit/Schema/ServerCapabilitiesTest.php b/tests/Unit/Schema/ServerCapabilitiesTest.php
index abb37dca..bb4e40ca 100644
--- a/tests/Unit/Schema/ServerCapabilitiesTest.php
+++ b/tests/Unit/Schema/ServerCapabilitiesTest.php
@@ -287,23 +287,29 @@ public function testJsonSerializeWithAllFeaturesEnabled(): void
         $json = $capabilities->jsonSerialize();
 
         $this->assertArrayHasKey('logging', $json);
-        $this->assertEquals(new \stdClass(), $json['logging']);
+        $this->assertEquals(new \stdClass(), $json['logging'] ?? null);
 
         $this->assertArrayHasKey('completions', $json);
-        $this->assertEquals(new \stdClass(), $json['completions']);
+        $this->assertEquals(new \stdClass(), $json['completions'] ?? null);
 
         $this->assertArrayHasKey('prompts', $json);
-        $this->assertTrue($json['prompts']->listChanged);
+        $prompts = $json['prompts'] ?? null;
+        $this->assertNotNull($prompts);
+        $this->assertTrue($prompts->listChanged);
 
         $this->assertArrayHasKey('resources', $json);
-        $this->assertTrue($json['resources']->subscribe);
-        $this->assertTrue($json['resources']->listChanged);
+        $resources = $json['resources'] ?? null;
+        $this->assertNotNull($resources);
+        $this->assertTrue($resources->subscribe);
+        $this->assertTrue($resources->listChanged);
 
         $this->assertArrayHasKey('tools', $json);
-        $this->assertTrue($json['tools']->listChanged);
+        $tools = $json['tools'] ?? null;
+        $this->assertNotNull($tools);
+        $this->assertTrue($tools->listChanged);
 
         $this->assertArrayHasKey('experimental', $json);
-        $this->assertEquals((object) $experimental, $json['experimental']);
+        $this->assertEquals((object) $experimental, $json['experimental'] ?? null);
     }
 
     public function testJsonSerializeWithFalseValues(): void
diff --git a/tests/Unit/Schema/ToolChoiceTest.php b/tests/Unit/Schema/ToolChoiceTest.php
index 2b5e7cd3..0b19fd3b 100644
--- a/tests/Unit/Schema/ToolChoiceTest.php
+++ b/tests/Unit/Schema/ToolChoiceTest.php
@@ -57,7 +57,6 @@ public function testNonStringModeIsRejected(): void
         $this->expectException(InvalidArgumentException::class);
         $this->expectExceptionMessage('Invalid "mode" in ToolChoice data.');
 
-        /* @phpstan-ignore argument.type */
         ToolChoice::fromArray(['mode' => 1]);
     }
 
@@ -66,7 +65,6 @@ public function testExplicitNullModeIsRejected(): void
         $this->expectException(InvalidArgumentException::class);
         $this->expectExceptionMessage('Invalid "mode" in ToolChoice data.');
 
-        /* @phpstan-ignore argument.type (deliberately null, as malformed wire data would be) */
         ToolChoice::fromArray(['mode' => null]);
     }
 }
diff --git a/tests/Unit/Schema/ToolTest.php b/tests/Unit/Schema/ToolTest.php
index 5169cb0c..30dcfa3b 100644
--- a/tests/Unit/Schema/ToolTest.php
+++ b/tests/Unit/Schema/ToolTest.php
@@ -62,7 +62,7 @@ public function testSerializationPlacesTitleBetweenNameAndInputSchema(?string $t
 
         $this->assertSame($expectedKeys, array_keys($serialized));
         if (null !== $title) {
-            $this->assertSame($title, $serialized['title']);
+            $this->assertSame($title, $serialized['title'] ?? null);
         } else {
             $this->assertArrayNotHasKey('title', $serialized);
         }
@@ -101,6 +101,45 @@ public function testRoundTripPreservesTitle(): void
         $this->assertSame($original->description, $restored->description);
     }
 
+    /**
+     * @param array<string, mixed> $inputSchema
+     */
+    #[DataProvider('provideMalformedInputSchemas')]
+    public function testConstructorRejectsMalformedInputSchemaMembers(array $inputSchema, string $expectedMessage): void
+    {
+        $this->expectException(InvalidArgumentException::class);
+        $this->expectExceptionMessage($expectedMessage);
+
+        new Tool(
+            name: 'broken',
+            title: null,
+            inputSchema: $inputSchema,
+            description: null,
+            annotations: null,
+        );
+    }
+
+    /**
+     * @return iterable<string, array{array<string, mixed>, string}>
+     */
+    public static function provideMalformedInputSchemas(): iterable
+    {
+        yield 'properties is a string' => [
+            ['type' => 'object', 'properties' => 'bad'],
+            'Tool inputSchema "properties" must be an object.',
+        ];
+
+        yield 'properties is a scalar' => [
+            ['type' => 'object', 'properties' => 42],
+            'Tool inputSchema "properties" must be an object.',
+        ];
+
+        yield 'required is a string' => [
+            ['type' => 'object', 'properties' => [], 'required' => 'bad'],
+            'Tool inputSchema "required" must be a list of property names.',
+        ];
+    }
+
     public function testConstructorNormalizesEmptyInputSchemaPropertiesToObject(): void
     {
         $tool = new Tool(
@@ -111,7 +150,7 @@ public function testConstructorNormalizesEmptyInputSchemaPropertiesToObject(): v
             annotations: null,
         );
 
-        $this->assertInstanceOf(\stdClass::class, $tool->inputSchema['properties']);
+        $this->assertInstanceOf(\stdClass::class, $tool->inputSchema['properties'] ?? null);
         $this->assertSame('{"name":"no_params","inputSchema":{"type":"object","properties":{},"required":null}}', json_encode($tool));
     }
 
@@ -123,7 +162,7 @@ public function testConstructorNormalizesEmptyPropertiesAfterJsonDecodeRoundTrip
 
         $tool = new Tool('t', null, $schema, null, null);
 
-        $this->assertInstanceOf(\stdClass::class, $tool->inputSchema['properties']);
+        $this->assertInstanceOf(\stdClass::class, $tool->inputSchema['properties'] ?? null);
         $this->assertStringContainsString('"properties":{}', (string) json_encode($tool));
     }
 
@@ -140,8 +179,12 @@ public function testFromArrayNormalizesNestedEmptyPropertiesRecursively(): void
             ],
         ]);
 
-        $this->assertInstanceOf(\stdClass::class, $tool->inputSchema['properties']['filter']['properties']);
-        $this->assertStringContainsString('"properties":{}', (string) json_encode($tool->inputSchema['properties']['filter']));
+        $properties = $tool->inputSchema['properties'] ?? null;
+        $this->assertIsArray($properties);
+        $filter = $properties['filter'] ?? null;
+        $this->assertIsArray($filter);
+        $this->assertInstanceOf(\stdClass::class, $filter['properties'] ?? null);
+        $this->assertStringContainsString('"properties":{}', (string) json_encode($filter));
     }
 
     public function testConstructorNormalizesEmptyOutputSchemaProperties(): void
@@ -155,7 +198,7 @@ public function testConstructorNormalizesEmptyOutputSchemaProperties(): void
             outputSchema: ['type' => 'object', 'properties' => []],
         );
 
-        $this->assertInstanceOf(\stdClass::class, $tool->outputSchema['properties']);
+        $this->assertInstanceOf(\stdClass::class, $tool->outputSchema['properties'] ?? null);
         $this->assertStringContainsString('"outputSchema":{"type":"object","properties":{}}', (string) json_encode($tool));
     }
 
@@ -178,7 +221,13 @@ public function testConstructorNormalizesEmptyPropertiesInsideArrayItems(): void
             annotations: null,
         );
 
-        $this->assertInstanceOf(\stdClass::class, $tool->inputSchema['properties']['rows']['items']['properties']);
+        $properties = $tool->inputSchema['properties'] ?? null;
+        $this->assertIsArray($properties);
+        $rows = $properties['rows'] ?? null;
+        $this->assertIsArray($rows);
+        $items = $rows['items'] ?? null;
+        $this->assertIsArray($items);
+        $this->assertInstanceOf(\stdClass::class, $items['properties'] ?? null);
     }
 
     /**
@@ -312,9 +361,9 @@ public function testRoundTripPreservesExecution(): void
             'execution' => ['taskSupport' => 'optional'],
         ];
 
-        $tool = Tool::fromArray(json_decode(json_encode($data), true));
+        $tool = Tool::fromArray(json_decode(json_encode($data, \JSON_THROW_ON_ERROR), true, flags: \JSON_THROW_ON_ERROR));
 
-        $this->assertJsonStringEqualsJsonString(json_encode($data), json_encode($tool));
+        $this->assertJsonStringEqualsJsonString(json_encode($data, \JSON_THROW_ON_ERROR), json_encode($tool, \JSON_THROW_ON_ERROR));
     }
 
     public function testExecutionIsOmittedWhenAbsent(): void
@@ -329,7 +378,7 @@ public function testEmptyExecutionSerializesAsObject(): void
     {
         $tool = new Tool('plain', null, ['type' => 'object', 'properties' => [], 'required' => null], null, null, execution: new ToolExecution());
 
-        $this->assertStringContainsString('"execution":{}', json_encode($tool));
+        $this->assertStringContainsString('"execution":{}', json_encode($tool, \JSON_THROW_ON_ERROR));
     }
 
     public function testFromArrayRejectsUnknownTaskSupport(): void
diff --git a/tests/Unit/Server/BuilderTest.php b/tests/Unit/Server/BuilderTest.php
index 25f1e125..0ca18360 100644
--- a/tests/Unit/Server/BuilderTest.php
+++ b/tests/Unit/Server/BuilderTest.php
@@ -374,6 +374,8 @@ private function extractServerInfo(Server $server): Implementation
 
         foreach ($requestHandlers as $handler) {
             if ($handler instanceof InitializeHandler) {
+                $this->assertNotNull($handler->configuration);
+
                 return $handler->configuration->serverInfo;
             }
         }
@@ -388,6 +390,8 @@ private function extractServerCapabilities(Server $server): ServerCapabilities
 
         foreach ($requestHandlers as $handler) {
             if ($handler instanceof InitializeHandler) {
+                $this->assertNotNull($handler->configuration);
+
                 return $handler->configuration->capabilities;
             }
         }
diff --git a/tests/Unit/Server/Handler/Request/CallToolHandlerTest.php b/tests/Unit/Server/Handler/Request/CallToolHandlerTest.php
index dd0f4984..dd66a6fd 100644
--- a/tests/Unit/Server/Handler/Request/CallToolHandlerTest.php
+++ b/tests/Unit/Server/Handler/Request/CallToolHandlerTest.php
@@ -563,6 +563,7 @@ public function testStructuredContentFollowsTheNegotiatedRevision(?string $negot
         $response = $this->handler->handle($request, $this->session);
 
         $this->assertInstanceOf(Response::class, $response);
+        $this->assertInstanceOf(CallToolResult::class, $response->result);
         $this->assertSame($expected, $response->result->structuredContent);
     }
 
@@ -668,6 +669,7 @@ public function testDeclaredOutputSchemaWithoutStructuredContentIsLogged(): void
         $response = $this->handler->handle($request, $this->session);
 
         $this->assertInstanceOf(Response::class, $response);
+        $this->assertInstanceOf(CallToolResult::class, $response->result);
         $this->assertNull($response->result->structuredContent);
     }
 
@@ -720,6 +722,7 @@ public function testStructuredContentMissingARequiredPropertyIsReportedAsAToolEr
         $response = $this->handler->handle($request, $this->session);
 
         $this->assertInstanceOf(Response::class, $response);
+        $this->assertInstanceOf(CallToolResult::class, $response->result);
         $this->assertTrue($response->result->isError);
         $this->assertNull($response->result->structuredContent);
         $this->assertStringContainsString("Invalid structured output for tool 'get_weather'", $this->firstText($response->result));
@@ -739,6 +742,7 @@ public function testStructuredContentOfTheWrongTypeIsReportedAsAToolError(): voi
         $response = $this->handler->handle($request, $this->session);
 
         $this->assertInstanceOf(Response::class, $response);
+        $this->assertInstanceOf(CallToolResult::class, $response->result);
         $this->assertTrue($response->result->isError);
         $this->assertStringContainsString("Invalid structured output for tool 'get_weather'", $this->firstText($response->result));
     }
@@ -756,6 +760,7 @@ public function testConformingStructuredContentIsSentUnchanged(): void
         $response = $this->handler->handle($request, $this->session);
 
         $this->assertInstanceOf(Response::class, $response);
+        $this->assertInstanceOf(CallToolResult::class, $response->result);
         $this->assertFalse($response->result->isError);
         $this->assertSame($structuredContent, $response->result->structuredContent);
     }
@@ -773,6 +778,7 @@ public function testStructuredContentIsNotValidatedWithoutAnOutputSchema(): void
         $response = $this->handler->handle($request, $this->session);
 
         $this->assertInstanceOf(Response::class, $response);
+        $this->assertInstanceOf(CallToolResult::class, $response->result);
         $this->assertFalse($response->result->isError);
         $this->assertSame($structuredContent, $response->result->structuredContent);
     }
@@ -789,6 +795,7 @@ public function testSelfBuiltResultIsValidatedAgainstTheOutputSchema(): void
         $response = $this->handler->handle($request, $this->session);
 
         $this->assertInstanceOf(Response::class, $response);
+        $this->assertInstanceOf(CallToolResult::class, $response->result);
         $this->assertNotSame($callToolResult, $response->result);
         $this->assertTrue($response->result->isError);
         $this->assertStringContainsString("Invalid structured output for tool 'get_weather'", $this->firstText($response->result));
@@ -806,6 +813,7 @@ public function testErrorResultIsNotValidatedAgainstTheOutputSchema(): void
         $response = $this->handler->handle($request, $this->session);
 
         $this->assertInstanceOf(Response::class, $response);
+        $this->assertInstanceOf(CallToolResult::class, $response->result);
         $this->assertSame($callToolResult, $response->result);
         $this->assertSame('The weather service is down.', $this->firstText($response->result));
     }
@@ -822,6 +830,7 @@ public function testEmptyArrayStructuredContentConformsToAnArrayOutputSchema():
         $response = $this->handler->handle($request, $this->session);
 
         $this->assertInstanceOf(Response::class, $response);
+        $this->assertInstanceOf(CallToolResult::class, $response->result);
         $this->assertFalse($response->result->isError);
         $this->assertSame([], $response->result->structuredContent);
     }
@@ -839,9 +848,10 @@ public function testEmptyObjectResultConformsToAnObjectOutputSchema(): void
         $response = $this->handler->handle($request, $this->session);
 
         $this->assertInstanceOf(Response::class, $response);
+        $this->assertInstanceOf(CallToolResult::class, $response->result);
         $this->assertFalse($response->result->isError);
         $this->assertEquals(new \stdClass(), $response->result->structuredContent);
-        $this->assertStringContainsString('"structuredContent":{}', json_encode($response->result));
+        $this->assertStringContainsString('"structuredContent":{}', json_encode($response->result, \JSON_THROW_ON_ERROR));
     }
 
     public function testSelfBuiltJsonSerializableStructuredContentIsValidatedAsSent(): void
@@ -866,8 +876,9 @@ public function jsonSerialize(): array
         $response = $this->handler->handle($request, $this->session);
 
         $this->assertInstanceOf(Response::class, $response);
+        $this->assertInstanceOf(CallToolResult::class, $response->result);
         $this->assertFalse($response->result->isError, $this->firstText($response->result));
-        $this->assertStringContainsString('"structuredContent":{"temperature":22.5,"conditions":"sunny"}', json_encode($response->result));
+        $this->assertStringContainsString('"structuredContent":{"temperature":22.5,"conditions":"sunny"}', json_encode($response->result, \JSON_THROW_ON_ERROR));
     }
 
     public function testNestedEmptyObjectIsValidatedAndSentAsAnObject(): void
@@ -899,8 +910,9 @@ public function __construct()
         $response = $this->handler->handle($request, $this->session);
 
         $this->assertInstanceOf(Response::class, $response);
+        $this->assertInstanceOf(CallToolResult::class, $response->result);
         $this->assertFalse($response->result->isError, $this->firstText($response->result));
-        $this->assertStringContainsString('"structuredContent":{"temperature":22.5,"meta":{}}', json_encode($response->result));
+        $this->assertStringContainsString('"structuredContent":{"temperature":22.5,"meta":{}}', json_encode($response->result, \JSON_THROW_ON_ERROR));
     }
 
     private function firstText(CallToolResult $result): string
@@ -927,6 +939,10 @@ private function createCallToolRequest(string $name, array $arguments): CallTool
         ]);
     }
 
+    /**
+     * @param array<string, mixed>|null $outputSchema
+     * @param list<non-empty-string>    $methodsToMock
+     */
     private function createToolReference(
         string $name,
         callable $handler,
diff --git a/tests/Unit/Server/Stateless/StatelessProtocolTest.php b/tests/Unit/Server/Stateless/StatelessProtocolTest.php
index 7d7d04c7..5770b178 100644
--- a/tests/Unit/Server/Stateless/StatelessProtocolTest.php
+++ b/tests/Unit/Server/Stateless/StatelessProtocolTest.php
@@ -306,8 +306,10 @@ public function testRemovedMethodsAreUnknown(string $method, array $params): voi
     private static function frames(StatelessResult $result): array
     {
         $frames = [];
+        $stream = $result->frames;
+        self::assertNotNull($stream);
 
-        foreach (($result->frames)() as $frame) {
+        foreach ($stream() as $frame) {
             if (null !== $frame) {
                 $frames[] = $frame;
             }
@@ -537,10 +539,15 @@ static function (RequestContext $context): string {
                     $gateway = $context->getClientGateway();
                     $schema = new ElicitationSchema(['v' => new StringSchemaDefinition('V')], ['v']);
 
-                    $when = $gateway->elicit('When?', $schema, key: 'when');
-                    $seat = $gateway->elicit('Seat?', $schema, key: 'seat');
+                    $when = $gateway->elicit('When?', $schema, key: 'when')->content['v'] ?? null;
+                    $seat = $gateway->elicit('Seat?', $schema, key: 'seat')->content['v'] ?? null;
 
-                    return $when->content['v'].'/'.$seat->content['v'];
+                    // Fail here rather than answering '/' and failing downstream.
+                    if (!\is_string($when) || !\is_string($seat)) {
+                        throw new \RuntimeException('An elicitation answer arrived without its value.');
+                    }
+
+                    return $when.'/'.$seat;
                 },
                 name: 'books_flight',
                 description: 'Asks twice before it answers',
@@ -861,6 +868,7 @@ public function testUndeclaredInputRequestIsRefusedWhenStreamed(): void
         $this->assertTrue($result->isStream());
 
         $frames = self::frames($result);
+        $this->assertNotEmpty($frames);
         $last = json_decode(json_encode($frames[array_key_last($frames)], \JSON_THROW_ON_ERROR), true, flags: \JSON_THROW_ON_ERROR);
 
         $this->assertSame(Error::MISSING_REQUIRED_CLIENT_CAPABILITY, $last['error']['code']);
@@ -963,8 +971,10 @@ public function testListenStreamDeliversSubscribedNotifications(): void
 
         $frames = [];
         $published = false;
+        $stream = $result->frames;
+        $this->assertNotNull($stream);
 
-        foreach (($result->frames)() as $frame) {
+        foreach ($stream() as $frame) {
             if (null === $frame) {
                 // Publish once the stream is established, so the notifications
                 // arrive the way a concurrent request would deliver them.
@@ -1033,7 +1043,10 @@ public function testAcknowledgmentReflectsWhatTheServerCanDo(): void
         ]);
 
         $first = null;
-        foreach (($result->frames)() as $frame) {
+        $stream = $result->frames;
+        $this->assertNotNull($stream);
+
+        foreach ($stream() as $frame) {
             if (null !== $frame) {
                 $first = $frame;
                 break;
diff --git a/tests/Unit/Server/Transport/Http/OAuth/JwtTokenValidatorTest.php b/tests/Unit/Server/Transport/Http/OAuth/JwtTokenValidatorTest.php
index 620ab228..10c4643a 100644
--- a/tests/Unit/Server/Transport/Http/OAuth/JwtTokenValidatorTest.php
+++ b/tests/Unit/Server/Transport/Http/OAuth/JwtTokenValidatorTest.php
@@ -288,7 +288,9 @@ public function testFromIssuerTagsKeysWithoutAlgorithmPerToken(): void
         $this->assertNotFalse($ec);
         openssl_pkey_export($ec, $ecPrivateKey);
         $ecDetails = openssl_pkey_get_details($ec);
-        $rsaDetails = openssl_pkey_get_details(openssl_pkey_get_public(self::$publicKey));
+        $rsaKey = openssl_pkey_get_public(self::$publicKey);
+        $this->assertNotFalse($rsaKey);
+        $rsaDetails = openssl_pkey_get_details($rsaKey);
         $this->assertIsArray($ecDetails);
         $this->assertIsArray($rsaDetails);
 
@@ -365,7 +367,9 @@ public function testFromIssuerRejectsInsecureIssuer(): void
      */
     private function jwksClient(Psr17Factory $factory, ?array $jwks = null, ?\ArrayObject $requested = null): ClientInterface
     {
-        $details = openssl_pkey_get_details(openssl_pkey_get_public(self::$publicKey));
+        $publicKey = openssl_pkey_get_public(self::$publicKey);
+        $this->assertNotFalse($publicKey);
+        $details = openssl_pkey_get_details($publicKey);
         $jwks ??= [[
             'kty' => 'RSA',
             'kid' => 'kid-1',
diff --git a/tests/Unit/Server/Transport/StdioTransportTest.php b/tests/Unit/Server/Transport/StdioTransportTest.php
index dbfcec2f..094b714a 100644
--- a/tests/Unit/Server/Transport/StdioTransportTest.php
+++ b/tests/Unit/Server/Transport/StdioTransportTest.php
@@ -83,6 +83,7 @@ private function createTransport(string $input, array &$messages, int $maxLineBy
     private function stream(string $contents)
     {
         $stream = fopen('php://temp', 'r+');
+        $this->assertNotFalse($stream);
         fwrite($stream, $contents);
         rewind($stream);