BitLogger/docs/changes/0.3.0.md

## BitLogger Update Changes

version 0.3.0

### Feature

- feat: add `config.mbt` as a minimal JSON-backed logger configuration layer
- feat: add `TextFormatterConfig`, `QueueConfig`, and `LoggerConfig` public config types
- feat: add `TextFormatterConfig::new(...)`, `QueueConfig::new(...)`, and `LoggerConfig::new(...)` constructors for explicit config assembly
- feat: add `SinkKind` and `SinkConfig` for sink-specific configuration
- feat: add `TextFormatterConfig::to_formatter()` for bridging parsed config into runtime formatter setup
- feat: add `parse_logger_config_text(...)` for JSON config parsing
- feat: add `logger_config_to_json(...)` and `stringify_logger_config(...)` for config serialization
- feat: add `RuntimeSink`, `ConfiguredLogger`, `build_logger(...)`, and `parse_and_build_logger(...)` for config-driven logger assembly
- feat: add `ConfiguredLogger::drain(...)`, `ConfiguredLogger::pending_count()`, and `ConfiguredLogger::dropped_count()` queue observability helpers
- feat: add `bitlogger_async/` as a separate native-target async adapter package
- feat: add `AsyncLogger`, `async_logger(...)`, `run()`, `wait_idle()`, `close()`, `pending_count()`, and `dropped_count()` on top of `moonbitlang/async`
- feat: add async logger composition helpers `with_context_fields(...)`, `with_filter(...)`, `with_patch(...)`, `with_target(...)`, `child(...)`, and `with_timestamp(...)`
- feat: add `AsyncLoggerBuildConfig`, `parse_async_logger_build_config_text(...)`, and `build_async_logger(...)` for config-driven async logger assembly
- feat: add async lifecycle helpers `shutdown()`, `is_closed()`, `is_running()`, `has_failed()`, and `last_error()` for safer worker teardown and observability
- feat: add `parse_async_logger_config_text(...)`, `stringify_async_logger_config(...)`, and build-config serialization helpers for async config roundtrip support
- feat: add async batching controls `max_batch` and `flush=Never|Batch|Shutdown` for queue draining and flush timing
- feat: expose `Record::new(...)` for adapter and integration layers
- fix: repair native file backend FFI declarations so native target checks succeed again
- feat: support config keys `min_level`, `target`, `timestamp`, `sink.kind`, `sink.path`, `sink.append`, `sink.auto_flush`, `sink.text_formatter`, and `queue`
- feat: support config-driven sink assembly for `console`, `json_console`, `text_console`, and `file`
- feat: use `maria/json_parser` as the first external dependency for practical config loading
- feat: add `TextFormatter.template` and `TextFormatterConfig.template` for template-driven text rendering
- feat: support formatter tokens `{timestamp}`, `{timestamp_ms}`, `{level}`, `{target}`, `{message}`, and `{fields}` in both runtime and JSON config paths
- feat: add `FileRotation`, `file_rotation(...)`, and size-based file rotation with retained backups for `file_sink(...)`
- feat: support `sink.rotation.max_bytes` and `sink.rotation.max_backups` in JSON logger config
- feat: add `FileSink::reopen()` and basic file sink failure counters via `open_failures()`, `write_failures()`, and `flush_failures()`
- feat: add `SplitSink`, `split_sink(...)`, and `split_by_level(...)` for routing records into different sinks by predicate or level
- feat: add `Logger::bind(...)` as an ergonomic context-binding alias and `fields(...)` helper for tuple-based field construction

### Test

- test: cover parsing of core logger config fields
- test: cover nested formatter and queue config parsing
- test: cover config stringify and parse roundtrip behavior
- test: cover config-built queued text logger flushing and pending count behavior
- test: cover partial drain behavior for config-built queued logger
- test: cover dropped-count reporting for bounded config-built queue
- test: cover template-based formatter rendering and disabled token behavior
- test: cover file rotation config parsing, config roundtrip, and native rotation behavior
- test: cover file sink reopen behavior and backend-dependent failure counter paths
- test: cover split sink predicate routing and level-based routing behavior
- test: cover `bind(...)` context composition and `fields(...)` helper behavior
- test: add async logger lifecycle, config roundtrip, and batching/flush policy test seeds
- build: verify `bitlogger_async --target native` and `examples/async_basic --target native` compile successfully

### Example

- docs: update `examples/basic` with JSON config loading example
- docs: update `examples/basic` to use `parse_and_build_logger(...)` with explicit error handling in `main`
- docs: add `examples/async_basic` to show async worker startup and queue-backed logging flow
- docs: update `examples/async_basic` to use unified JSON-driven async logger config
- docs: update root README, English README, and Mooncake README with config usage notes
- docs: update formatter examples to demonstrate template-based text rendering
- docs: update file sink examples to demonstrate rotation and backup retention
- docs: document file sink reopen and observability counters in README variants
- docs: add split sink examples for level-based routing
- docs: add `bind(...)` examples for reusable context binding
- docs: update root README and English README with async adapter notes and current scope
- chore: ignore local `.mooncakes/` cache directory in git

### Notes

- current config scope is still intentionally constrained to stable built-in sink shapes
- formatter templates are intentionally limited to simple token replacement and do not yet include conditional blocks or alignment/padding controls
- current file rotation scope is intentionally limited to size-based rename retention and does not yet include time rotation or compression
- file sink observability is currently counter-based and explicit; it does not yet attempt automatic recovery or background self-healing
- queue wrapping remains synchronous drain-based delivery, not async runtime scheduling
- async logging remains an isolated adapter layer and currently targets `native/llvm` only