- Introduced `getEnvOrPanic` helper to enforce non-empty required environment variables.
- Added strict validation for server (`HOP_SERVER_*`) and client (`HOP_CLIENT_*`) configurations at startup.
- Updated `.env` loader to prioritize OS env vars over `.env` file values.
- Enhanced structured logging for validated environment variables.
- Improved Makefile with `check-env-server` and `check-env-client` targets for build-time validation.
- Updated description of server-client transport to use Protobuf-based, length-prefixed envelopes.
- Revised notes on handling large HTTP bodies and outlined plans for stream/frame-based tunneling.
- Updated `progress.md` with finalized implementation of MTU-safe chunk size constant.
- Documented the custom `.env` loader behavior, prioritization of OS-level environment variables, and validation stages.
- Explained server and client-specific configuration loading process.
- Added best practices for environment variable usage in development and production environments.
- Designed a stream/frame-based protocol leveraging `StreamOpen`, `StreamData`, and `StreamClose` fields for chunked transmission.
- Addressed DTLS/UDP MTU limits by capping tunneled body sizes to 48 KiB and replacing oversized responses with `502 Bad Gateway`.
- Updated `internal/protocol` to enable safe handling of large HTTP bodies via streaming.
- Documented future work on replacing JSON with binary encoding for improved performance.
