- error.rs: Structured error types with context for all subsystems
(transport, routing, crypto, protocol, store, config)
- config.rs: Runtime configuration with TOML parsing and validation
- metrics.rs: Counter/gauge/histogram metrics with transport-specific
tracking and JSON-serializable snapshots
- rate_limit.rs: Token bucket rate limiting with per-peer tracking,
duty cycle enforcement for LoRa, and backpressure control
These modules provide the foundation for production deployment.