Add CLAUDE.md

Author: goerz

CLAUDE.md

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+# CLAUDE.md
+
+This file provides guidance to Claude Code (claude.ai/code) when working with code in this repository.
+
+## Commands
+
+### Testing and Development
+- `make test` - Run the complete test suite in a subprocess with coverage
+- `julia --project=test --banner=no --startup-file=yes -e 'include("devrepl.jl"); test()'` - Run tests directly
+- `include("test/runtests.jl")` - Run tests from within Julia REPL
+
+### Code Quality and Formatting
+- `make codestyle` - Apply JuliaFormatter to the entire project
+
+### Documentation
+- `make docs` - Build the documentation using Documenter.jl
+- `include("docs/make.jl")` - Build docs from within Julia REPL
+
+### Maintenance
+- `make clean` - Clean up build/doc/testing artifacts
+- `make distclean` - Restore to a clean checkout state
+
+## Package Architecture
+
+### Core Framework Structure
+QuantumControl.jl is a high-level interface package that provides a coherent API for quantum dynamics and control. It re-exports functionality from QuantumPropagators.jl and organizes quantum control workflows.
+
+### Key Components
+
+**Main Module Structure:**
+- `src/QuantumControl.jl` - Main module with submodules for Generators, Controls, Shapes, Storage, Amplitudes, and Interfaces
+- Re-exports QuantumPropagators functionality through organized submodules
+- Each submodule uses `@reexport_members` macro to expose underlying functionality
+
+**Core Abstractions:**
+- `ControlProblem` (`src/control_problem.jl`) - Defines multi-trajectory optimization problems
+- `Trajectory` (`src/trajectories.jl`) - Describes time evolution of quantum states under generators
+- `optimize` (`src/optimize.jl`) - Main optimization interface that delegates to specific methods (Krotov, GRAPE, etc.)
+
+**Supporting Infrastructure:**
+- `src/functionals.jl` - Optimization functionals submodule
+- `src/pulse_parameterizations.jl` - Pulse parameterization utilities
+- `src/workflows.jl` - High-level workflow utilities (run_or_load, save/load optimization)
+- `src/callbacks.jl` - Optimization callback system
+- `src/interfaces/` - Interface validation for amplitudes and generators
+
+### Development Environment
+- Uses `devrepl.jl` for development setup with automatic package installation
+- Test environment in `test/` with comprehensive suite covering all major functionality
+- Documentation system uses Documenter.jl with custom themes and API generation
+
+### Dependencies and Extensions
+- Core dependency: QuantumPropagators.jl for propagation functionality
+- Optional extensions for FiniteDifferences.jl and Zygote.jl for automatic differentiation
+- Integration with optimization packages (Krotov.jl, GRAPE.jl) via method dispatch
+
+### Testing Strategy
+- Comprehensive test suite with SafeTestsets for isolation
+- Tests for interfaces, propagation, optimization, parameterization, and workflows
+- Coverage reporting and CI integration
+- Downstream testing of Krotov and GRAPE packages