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+# Borealis Engine Overview
+
+The Engine is an additive server stack that will ultimately replace the legacy Flask app under `Data/Server`.  It is safe to run the Engine entrypoint (`Data/Engine/bootstrapper.py`) side-by-side with the legacy server while we migrate functionality feature-by-feature.
+
+## Environment configuration
+
+The Engine mirrors the legacy defaults so it can boot without additional configuration.  These environment variables are read by `Data/Engine/config/environment.py`:
+
+| Variable | Purpose | Default |
+| --- | --- | --- |
+| `BOREALIS_ROOT` | Overrides automatic project root detection.  Useful when running from a packaged location. | Directory two levels above `Data/Engine/` |
+| `BOREALIS_DATABASE_PATH` | Path to the SQLite database. | `<project_root>/database.db` |
+| `BOREALIS_STATIC_ROOT` | Directory that serves static assets for the SPA. | `<project_root>/Data/Server/dist` |
+| `BOREALIS_CORS_ALLOWED_ORIGINS` | Comma-delimited list of origins granted CORS access. Use `*` for all origins. | `*` |
+| `BOREALIS_FLASK_SECRET_KEY` | Secret key for Flask session signing. | `change-me` |
+| `BOREALIS_DEBUG` | Enables debug logging, disables secure-cookie requirements, and allows Werkzeug debug mode. | `false` |
+| `BOREALIS_HOST` | Bind address for the HTTP/Socket.IO server. | `127.0.0.1` |
+| `BOREALIS_PORT` | Bind port for the HTTP/Socket.IO server. | `5000` |
+
+## Logging expectations
+
+`Data/Engine/config/logging.py` configures a timed rotating file handler that writes to `Logs/Server/engine.log`.  Each entry follows the `<timestamp>-engine-<message>` format required by the project logging policy.  The handler is attached to both the Engine logger (`borealis.engine`) and the root logger so that third-party frameworks share the same log destination.
+
+## Bootstrapping flow
+
+1. `Data/Engine/bootstrapper.py` loads the environment, configures logging, and builds the Flask application via `Data/Engine/server.py`.
+2. Placeholder HTTP and Socket.IO registration hooks run so the Engine can start without any migrated routes yet.
+3. The resulting runtime object exposes the Flask app, resolved settings, and optional Socket.IO server.  `bootstrapper.main()` runs the appropriate server based on whether Socket.IO is present.
+
+As migration continues, services, repositories, interfaces, and integrations will live under their respective subpackages while maintaining isolation from the legacy server.