Release v0.8.0

Added - 0.8.0

• Runtime-agnostic async support (async feature)

  • New async_ext module with core async types

  • FutureResultExt trait providing .ctx() and .with_ctx() methods on Future<Output = Result<T, E>>

  • ContextFuture wrapper for lazy error context evaluation (cancel-safe)

  • AsyncErrorPipeline for chainable async error handling operations

  • prelude_async module re-exporting all prelude items plus async-specific functionality

  • rail_async! macro for wrapping async operations into AsyncErrorPipeline

  • ctx_async! macro for attaching formatted context to futures ergonomically

  • Added docs/QUICK_START_ASYNC.md with async usage patterns and best practices

• Async validation support (async feature)

  • validate_all_async<I> function for running multiple async validations sequentially and accumulating all errors

  • validate_seq_async function for sequential validation where each step depends on previous result

  • Runtime-neutral design mirroring synchronous Validation semantics

• Async retry support (async feature)

  • RetryPolicy trait for pluggable retry strategies

  • ExponentialBackoff policy with builder pattern (with_initial_delay, with_max_delay, with_max_attempts, with_multiplier)

  • FixedDelay policy for constant-delay retries

  • retry_with_policy function: runtime-agnostic retry loop accepting custom sleep_fn

  • retry_with_metadata function returning RetryResult<T, E> with result, attempts, and total_wait_time

  • Structured context on failure (e.g., "exhausted N retry attempts", "permanent error, no retry")

• Tokio integration (tokio feature)

  • retry_transient convenience function using tokio::time::sleep

  • retry_transient_n for simple retry with attempt count

  • try_with_timeout wrapper returning TimeoutResult<T, E>

  • TimeoutResult enum with Ok, Err, and Timeout variants

  • TimeoutError type for timeout representation

• Tower integration (tower feature)

  • ErrorRailLayer: Tower Layer wrapping service errors in ComposableError with context

  • ErrorRailService: Tower Service wrapper for error context attachment

  • ErrorRailFuture: Future wrapper for lazy context evaluation

  • ServiceErrorExt trait providing .with_error_context() extension for any Service

• Tracing integration (tracing feature)

  • FutureSpanExt trait providing .with_span_context() and .with_span() for futures

  • ResultSpanExt trait providing .with_current_span() and .with_span() for Results

  • SpanContextFuture: Future wrapper capturing span context on error

  • instrument_error function to add current span context to any error

• Feature flag layout

  • tokio, tower, and tracing features are independently configurable

  • ecosystem is a convenience bundle enabling tokio + tower + tracing

• Comprehensive test coverage for async functionality

  • tests/async_ext/future_ext_tests.rs: lazy evaluation and context chaining

  • tests/async_ext/pipeline_tests.rs: AsyncErrorPipeline operations

  • tests/async_ext/validation_tests.rs: all-valid, some-invalid, and sequential validation scenarios

  • tests/async_ext/retry_tests.rs: transient/permanent errors and exhausted attempts

  • tests/async_ext/tokio_tests.rs: Tokio-specific retry and timeout functionality

  • tests/async_ext/tracing_tests.rs: span context attachment

• New examples

  • examples/async_api_patterns.rs: demonstrates 7 common async error handling patterns

  • examples/async_tower_integration.rs: demonstrates Tower layer and service usage