Create CLAUDE.md for Codebase Guidance

Summary

Please analyze this codebase and create a CLAUDE.md file, which will be given to future instances of Claude Code to operate in this repository.

What to add:

Commands that will be commonly used, such as how to build, lint, and run tests. Include the necessary commands to develop in this codebase, such as how to run a single test.
High-level code architecture and structure so that future instances can be productive more quickly. Focus on the "big picture" architecture that requires reading multiple files to understand.

Usage notes:

If there's already a CLAUDE.md, suggest improvements to it.
When you make the initial CLAUDE.md, do not repeat yourself and do not include obvious instructions like "Provide helpful error messages to users", "Write unit tests for all new utilities", "Never include sensitive information (API keys, tokens) in code or commits".
Avoid listing every component or file structure that can be easily discovered.
Don't include generic development practices.
If there are Cursor rules (in .cursor/rules/ or .cursorrules) or Copilot rules (in .github/copilot-instructions.md), make sure to include the important parts.
If there is a README.md, make sure to include the important parts.
Do not make up information such as "Common Development Tasks", "Tips for Development", "Support and Documentation" unless this is expressly included in other files that you read.
Be sure to prefix the file with the following text:

# CLAUDE.md

This file provides guidance to Claude Code (claude.ai/code) when working with code in this repository.

Your account does not have access to Claude Code. Please run /login.

Please analyze this codebase and create a CLAUDE.md file, which will be given to future instances of Claude Code to operate in this repository.

What to add:

Commands that will be commonly used, such as how to build, lint, and run tests. Include the necessary commands to develop in this codebase, such as how to run a single test.
High-level code architecture and structure so that future instances can be productive more quickly. Focus on the "big picture" architecture that requires reading multiple files to understand.

Usage notes:

If there's already a CLAUDE.md, suggest improvements to it.
When you make the initial CLAUDE.md, do not repeat yourself and do not include obvious instructions like "Provide helpful error messages to users", "Write unit tests for all new utilities", "Never include sensitive information (API keys, tokens) in code or commits".
Avoid listing every component or file structure that can be easily discovered.
Don't include generic development practices.
If there are Cursor rules (in .cursor/rules/ or .cursorrules) or Copilot rules (in .github/copilot-instructions.md), make sure to include the important parts.
If there is a README.md, make sure to include the important parts.
Do not make up information such as "Common Development Tasks", "Tips for Development", "Support and Documentation" unless this is expressly included in other files that you read.
Be sure to prefix the file with the following text:

# CLAUDE.md

This file provides guidance to Claude Code (claude.ai/code) when working with code in this repository.

I'll analyze the codebase in parallel to understand its structure, build system, and architecture.

Now let me read a few key files directly for accuracy.

The agent hit an error but returned useful data. Let me read a few more key files directly.

Now let me check the Mage.Tests pom.xml for surefire configuration and how to run a single test.

Let me also look at how sets register their cards and the card file naming convention.

Now I have enough information. Let me create the CLAUDE.md file.

Created CLAUDE.md with:

Build commands — make build, mvn test, single test execution with -Dtest= and -pl Mage.Tests
Module architecture — All 9 modules with their purpose and package structure
Card implementation pattern — Complete example with conventions (final class, copy constructor, singleton keyword abilities, filter patterns)
Core abstractions — Ability/Effect hierarchy, 7-layer continuous effect system, key constants
SubType gotcha — byDescription() for card code vs fromString() for tests only
Test framework — Full example test with the declarative API, all key assertion/action methods, test file organization
Event system and plugin architecture — How game variants and extensions work

<task-notification> <task-id>a3064fb</task-id> <status>failed</status> <summary>Agent "Explore test and card patterns" failed: classifyHandoffIfNeeded is not defined</summary> </task-notification> Full transcript available at: /tmp/claude-1000/-mnt-dest-btrfs-home-jc-src-mage/tasks/a3064fb.output

The background agent failed but I had already gathered all the information I needed from it and other sources. The CLAUDE.md file has been created successfully at the repository root.