feat: add Fabric patterns support

[OskarStark]

Summary

This PR implements support for Fabric patterns in LLM Chain, providing access to a comprehensive collection of pre-built, tested system prompts for common AI tasks.

Implementation Details

Core Components

1. Message::fabric() Factory Method

   • Simple API for using Fabric patterns: Message::fabric('create_summary')
   • Supports custom pattern locations
   • Automatically loads patterns from the php-llm/fabric-pattern package

2. FabricInputProcessor

   • Enables dynamic pattern loading via chain options
   • Usage: $chain->call($messages, ['fabric_pattern' => 'analyze_code'])
   • Can be configured with custom pattern repositories

3. FabricRepository

   • Manages pattern loading and caching
   • Validates pattern existence
   • Supports metadata loading (README.md, metadata.json)
   • Checks for php-llm/fabric-pattern package installation

4. Exception Handling

   • Clear error messages when the patterns package is not installed
   • PatternNotFoundException for missing patterns

Design Decisions

1. Separate Package Requirement

   • Fabric patterns are provided by the php-llm/fabric-pattern package
   • Keeps the main library lightweight
   • Users can opt-in to Fabric functionality
   • Clear error messages guide users to install the package

2. Multiple Usage Patterns

   • Factory method for simple, static usage
   • Input processor for dynamic, runtime pattern selection
   • Both approaches support custom pattern locations

3. Immutable Design

   • Follows the library's immutable patterns (e.g., MessageBag)
   • Repository uses internal caching for performance

Usage Examples

Via Factory Method

$messages = new MessageBag(
    Message::fabric('create_summary'),
    Message::ofUser($articleContent)
);
$response = $chain->call($messages);

Via Input Processor

$processor = new FabricInputProcessor();
$chain = new Chain($platform, $model, [$processor]);

$response = $chain->call($messages, ['fabric_pattern' => 'analyze_threat_report']);

Custom Pattern Location

$repository = new FabricRepository('/path/to/custom/patterns');
$processor = new FabricInputProcessor($repository);

Documentation

• Added comprehensive section to README.md
• Created example files in examples/fabric/
• Included PHPDoc comments with usage instructions

Testing

• Full test coverage for all new classes
• Tests handle the case when the patterns package is not installed
• Mock-friendly design (removed final from FabricRepository)

Available Patterns

Some popular patterns include:

• create_summary - Create comprehensive summaries
• analyze_claims - Fact-check and analyze claims
• extract_wisdom - Extract key insights
• improve_writing - Enhance writing quality
• analyze_code - Security and quality analysis

Closes #31

🤖 Generated with Claude Code

[DZunke]

What is happening if the MessageBag already have a System Message? I think most models can handle having multiple system messages. I have read some models do not care about the role of a message and take everything the same. But are we clear about possible problems when adding a system message to a bag that is already containing a system message? 🤔

[OskarStark]

Right now, same with the SystemInputProcessor, only one SystemMessage is supported by llm-chain

[DZunke]

Could this maybe be improved by checking for the existence of the pattern class from this package? For me checking directory hierarchie feels a bit unstable. And utilizing the pattern path btw. the loader from this class the library is delivering?

https://github.com/php-llm/fabric-pattern/blob/main/src/Pattern.php

[OskarStark]

I would say yes, also not super happy right now with this extra package, maybe it's better to get all the data and check it in into the fabric-pattern repository by mentioning the copyright etc. or having a command to download the fabrics upfront and use this path. not sure yet