Tool handle() receives named args causing 'Unknown named parameter' when using Laravel AI SDK's ->using() closure

[h-shvedko]

Bug Description

When tools are executed via CallsTools::executeToolCall(), the tool arguments are passed as named parameters through call_user_func_array(), which then get spread to the ->using() closure as named args. Since the closure typically has a generic parameter name like $arguments, PHP throws Unknown named parameter $path (or whatever the tool's first param is).

The error is silently caught by PrismException in executeToolCall() (line 175) and converted to a tool error result. The LLM then sees a "Parameter validation error" and retries, creating an infinite retry loop until maxSteps is exhausted.

Reproduction

$tool = (new \Prism\Prism\Tool)
    ->as('write_file')
    ->for('Write a file')
    ->withStringParameter('path', 'File path')
    ->withStringParameter('content', 'File content')
    ->using(fn ($arguments) => 'wrote file: ' . json_encode($arguments))
    ->withoutErrorHandling();

// Simulating what CallsTools::executeToolCall does:
$toolCall = new \Prism\Prism\ValueObjects\ToolCall(
    id: 'test',
    name: 'write_file',
    arguments: ['path' => 'test.txt', 'content' => 'hello world'],
);

// This throws "Unknown named parameter $path"
$output = call_user_func_array(
    $tool->handle(...),
    $toolCall->arguments()  // Returns ['path' => '...', 'content' => '...']
);

Root Cause

In src/Concerns/CallsTools.php line 134-136:

$output = call_user_func_array(
    $tool->handle(...),
    $toolCall->arguments()
);

$toolCall->arguments() returns an associative array like ['path' => 'test.txt', 'content' => 'hello']. When passed through call_user_func_array, PHP treats these as named arguments to Tool::handle(...$args).

Inside Tool::handle() (line 264), call_user_func($this->fn, ...$args) then spreads these named args to the ->using() closure. Since the closure parameter is typically named $arguments (not $path), PHP throws Unknown named parameter $path.

Impact

• All tools with >1 parameter are affected when using the ->using() closure pattern
• The error is silently caught by PrismException handler in executeToolCall(), making it invisible
• The LLM sees "Parameter validation error" and retries until maxSteps is exhausted
• Tools that work around this (e.g., using named params matching the tool schema) are unaffected

Affected Code

• src/Concerns/CallsTools.php:134-136 — call_user_func_array with named args
• src/Tool.php:264 — call_user_func($this->fn, ...$args) spreading named args to closure

Suggested Fix

In CallsTools::executeToolCall(), wrap arguments in a positional array before calling:

// Before (broken):
$output = call_user_func_array(
    $tool->handle(...),
    $toolCall->arguments()
);

// After (fixed):
$output = $tool->handle($toolCall->arguments());

Or in Tool::handle(), normalize $args to a single positional array:

public function handle(...$args): string|ToolOutput
{
    try {
        // Normalize: if named args were spread, recombine into single array
        $arguments = count($args) === 1 && is_array($args[0]) ? $args[0] : $args;
        $value = call_user_func($this->fn, $arguments);
        // ...

Environment

• prism-php/prism: v0.99.22
• laravel/ai: v0.2.8
• PHP: 8.4
• Provider: Anthropic (Claude)