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Agent Context & Message Compilers

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AgentContext

AgentContext holds the conversation data: messages, system prompt, metadata, and an optional response format. 
$state = AgentState::empty()
    ->withSystemPrompt('You are a helpful assistant.')
    ->withMetadata('session_id', 'abc');

// Access
$state->context()->systemPrompt();
$state->context()->messages();
$state->context()->metadata();
// @doctest id="921c"

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Message Compilers

Before each LLM call, the driver uses a CanCompileMessages implementation to transform AgentState into the final Messages sent to the LLM. 
interface CanCompileMessages
{
    public function compile(AgentState $state): Messages;
}
// @doctest id="5680"
The default compiler assembles messages from the agent’s context. You can replace it to control exactly what the LLM sees.

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Custom Compiler

Implement CanCompileMessages for custom message assembly: 
use Cognesy\Agents\Context\CanCompileMessages;
use Cognesy\Agents\Core\Data\AgentState;
use Cognesy\Messages\Messages;

class MyCompiler implements CanCompileMessages
{
    public function compile(AgentState $state): Messages
    {
        // Custom logic to build messages from state
        return $state->messages();
    }
}
// @doctest id="c773"
Inject it into the loop’s driver: 
$driver = new ToolCallingDriver(messageCompiler: new MyCompiler());
$loop = AgentLoop::default()->withDriver($driver);
// @doctest id="7e7f"