clock-curve-math 0.6.0

# API Stability Assessment - Version 0.6.0-rc.1

## Executive Summary

The `clock-curve-math` library API has been assessed for stability and is ready for the 0.6.0 release. All public APIs are well-designed, consistent, and backward-compatible.

## Assessment Methodology

- **Code Review**: Examined all public modules, traits, and functions
- **Feature Compatibility**: Tested all feature flag combinations (bigint-backend, custom-limbs, serde, rand, alloc, std)
- **Cross-Platform Testing**: Validated across multiple architectures (x86_64, aarch64, riscv64, armv7, powerpc64, embedded)
- **Test Coverage**: All 103+ unit tests pass across all configurations

## Public API Inventory

### Core Types
- **`FieldElement`**: Montgomery-form field element (mod p = 2^255 - 19)
- **`Scalar`**: Montgomery-form scalar (mod l = 2^252 + 27742317777372353535851937790883648493)
- **`BigInt`**: Big integer arithmetic with constant-time operations

### Traits
- **`FieldOps`**: Arithmetic operations for field elements
- **`ScalarOps`**: Arithmetic operations for scalars
- **`MontgomeryOps`**: Montgomery arithmetic operations
- **`BigIntOps`**: Big integer operations

### Error Handling
- **`MathError`**: Comprehensive error enumeration with detailed error types
- **Validation Functions**: `validate_*` functions for input checking

### Constant-Time Operations
- **Comparison Functions**: `ct_eq`, `ct_neq`, `ct_lt`, `ct_gt`, `ct_is_zero`
- **Selection Operations**: `ct_select`, `ct_select_array`, `ct_swap`, `ct_mask`

### Advanced Operations (alloc feature)
- **Batch Operations**: `batch_inverse`, `multi_exp`, `multi_exp_windowed`
- **Square Root**: `sqrt` with Legendre symbol computation
- **Serialization**: Serde support when enabled

## Stability Assessment

### ✅ Stable APIs

1. **Core Arithmetic Types**
   - `FieldElement` and `Scalar` constructors and methods are stable
   - All arithmetic operations (`add`, `sub`, `mul`, `square`, `inv`) are stable
   - Serialization (`to_bytes`/`from_bytes`) is stable

2. **Traits**
   - `FieldOps` and `ScalarOps` traits are stable
   - Method signatures are consistent and well-documented

3. **Error Handling**
   - `MathError` enum variants are stable
   - Error propagation is consistent across the API

4. **Constant-Time Operations**
   - All `ct_*` functions have stable signatures
   - Behavior is guaranteed constant-time

5. **Validation Functions**
   - All `validate_*` functions are stable
   - Return consistent `Result<(), MathError>` types

### ⚠️ Areas of Caution

1. **Advanced Operations**
   - Batch operations require `alloc` feature
   - Some functions return custom result types (e.g., `BatchInverseResult`)

2. **Backend Selection**
   - `bigint-backend` vs `custom-limbs` may have performance differences
   - APIs remain consistent regardless of backend

## Feature Flag Compatibility

All feature combinations tested successfully:

| Configuration | Status | Notes |
|---------------|--------|-------|
| Default (bigint-backend + alloc) | ✅ | Full functionality |
| `custom-limbs` | ✅ | no_std compatible |
| `custom-limbs + alloc` | ✅ | Advanced operations available |
| `serde` | ✅ | Serialization support |
| `rand` | ✅ | Random generation support |
| `std` | ✅ | Full standard library support |

## Breaking Change Analysis

### No Breaking Changes Required

1. **API Consistency**: All public APIs follow consistent patterns
2. **Feature Flags**: Optional features don't break core functionality
3. **Error Handling**: Error types are comprehensive and stable
4. **Naming Conventions**: Function and type names are descriptive and consistent

### Recommended Future Considerations

1. **Deprecation Planning**: Consider deprecation warnings for any future breaking changes
2. **Semantic Versioning**: Strict adherence to semver for future releases
3. **Migration Guides**: Provide clear migration paths if breaking changes become necessary

## Backward Compatibility Guarantees

### 0.6.0 Release Guarantees

1. **API Stability**: All public APIs in 0.6.0 will remain stable until 1.0.0
2. **Feature Compatibility**: All documented feature combinations will continue to work
3. **Error Compatibility**: Error types and meanings will remain consistent
4. **Performance**: Constant-time guarantees will be maintained

### Breaking Change Policy

Breaking changes will only occur:
- In major version bumps (0.x → 1.x)
- With explicit deprecation warnings in prior releases
- With comprehensive migration documentation
- Only when absolutely necessary for security or correctness

## Recommendations

1. **Proceed to 0.6.0-rc.1**: API is stable and ready for release candidate
2. **Document Stability Guarantees**: Update README and documentation with stability promises
3. **Prepare for Ecosystem Integration**: APIs are ready for external integration testing
4. **Plan Deprecation Strategy**: Establish clear deprecation policies for future versions

## Conclusion

The `clock-curve-math` library has achieved API stability for the 0.6.0 release. All public interfaces are well-designed, consistent, and thoroughly tested. The library is ready to proceed to the release candidate phase with confidence in API stability.