Add CLAUDE.md with development guidance

.claude/settings.json

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+{
+  "permissions": {
+    "allow": [
+      "Bash(uv run pytest:*)",
+      "Bash(uv run mypy:*)",
+      "Bash(uv run pre-commit:*)"
+
+    ],
+    "deny": []
+  }
+}

AGENTS.md

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+# AGENTS.md
+
+See @CLAUDE.md for AI coding agent instructions.

CLAUDE.md

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+# CLAUDE.md
+
+This file provides guidance to AI coding agents when working with code in this repository.
+
+## Project Overview
+
+Pluggy is a minimalist production-ready plugin system that serves as the core framework for pytest, datasette and devpi.
+It provides hook specification and implementation mechanisms through a plugin manager system.
+
+## Development Commands
+
+All commands use `uv run` for consistent environments.
+
+### Testing
+- `uv run pytest` - Run all tests (prefer running all tests for quick feedback)
+- `uv run pytest testing/benchmark.py` - Run benchmark tests
+
+### Code Quality
+- `uv run pre-commit run -a` - Run all pre-commit hooks (linting, formatting, type checking)
+- Always reread files modified by pre-commit
+
+## Development Process
+
+- Always read `src/pluggy/*.py` to get a full picture
+- Consider backward compatibility
+- Always run all tests: `uv run pytest`
+- Always run pre-commit before committing: `uv run pre-commit run -a`
+- Prefer running full pre-commit over individual tools (ruff/mypy)
+
+
+
+## Core Architecture
+
+### Main Components
+
+- **PluginManager** (`src/pluggy/_manager.py`): Central registry that manages plugins and coordinates hook calls
+- **HookCaller** (`src/pluggy/_hooks.py`): Executes hook implementations with proper argument binding
+- **HookImpl/HookSpec** (`src/pluggy/_hooks.py`): Represent hook implementations and specifications
+- **Result** (`src/pluggy/_result.py`): Handles hook call results and exception propagation
+- **Multicall** (`src/pluggy/_callers.py`): Core execution engine for calling multiple hook implementations
+
+### Package Structure
+- `src/pluggy/` - Main package source
+- `testing/` - Test suite using pytest
+- `docs/` - Sphinx documentation and examples
+- `changelog/` - Towncrier fragments for changelog generation
+
+## Configuration Files
+- `pyproject.toml` - Project metadata, build system, tool configuration (ruff, mypy, setuptools-scm)
+- `tox.ini` - Multi-environment testing configuration
+- `.pre-commit-config.yaml` - Code quality automation (ruff, mypy, flake8, etc.)