Require Eventlet for Engine runtime

Data/Engine/server.py

@@ -9,6 +9,7 @@ error log) to align with the project's operational practices.
 """
 from __future__ import annotations
 
+import importlib.util
 import logging
 import ssl
 import sys
@@ -16,27 +17,31 @@ from dataclasses import dataclass
 from pathlib import Path
 from typing import Any, Mapping, Optional, Sequence, Tuple
 
-try:  # pragma: no-cover - optional dependency when running without eventlet
-    import eventlet  # type: ignore
-except Exception:  # pragma: no-cover - fall back to threading mode
-    eventlet = None  # type: ignore[assignment]
-    logging.getLogger(__name__).warning(
-        "Eventlet is not available; Engine will run Socket.IO in threading mode."
+
+def _require_dependency(module: str, friendly_name: str) -> None:
+    if importlib.util.find_spec(module) is None:  # pragma: no cover - import check
+        raise RuntimeError(
+            f"{friendly_name} (Python module '{module}') is required for the Borealis Engine runtime. "
+            "Install the packaged dependencies by running Borealis.ps1 or ensure the module is present in the active environment."
         )
-else:  # pragma: no-cover - monkey patch only when eventlet is present
-    eventlet.monkey_patch(thread=False)
 
-from flask import Flask, request
-from flask_cors import CORS
-from flask_socketio import SocketIO
-from werkzeug.middleware.proxy_fix import ProxyFix
 
-if eventlet:
-    try:  # pragma: no-cover - defensive import mirroring the legacy runtime.
-        from eventlet.wsgi import HttpProtocol  # type: ignore
-    except Exception:  # pragma: no-cover - the Engine should still operate without it.
-        HttpProtocol = None  # type: ignore[assignment]
-    else:
+_require_dependency("eventlet", "Eventlet")
+_require_dependency("flask", "Flask")
+_require_dependency("flask_socketio", "Flask-SocketIO")
+
+import eventlet  # type: ignore  # noqa: E402  # pragma: no cover - import guarded above
+from eventlet import wsgi as eventlet_wsgi  # type: ignore  # noqa: E402  # pragma: no cover
+
+from flask import Flask, request  # noqa: E402
+from flask_cors import CORS  # noqa: E402
+from flask_socketio import SocketIO  # noqa: E402
+from werkzeug.middleware.proxy_fix import ProxyFix  # noqa: E402
+
+eventlet.monkey_patch(thread=False)  # pragma: no cover - aligns with legacy runtime
+
+HttpProtocol = getattr(eventlet_wsgi, "HttpProtocol", None)
+if HttpProtocol is not None:  # pragma: no branch - attribute exists in supported versions
     _original_handle_one_request = HttpProtocol.handle_one_request
 
     def _quiet_tls_http_mismatch(self):  # type: ignore[override]
@@ -78,10 +83,8 @@ if eventlet:
             return None
 
     HttpProtocol.handle_one_request = _quiet_tls_http_mismatch  # type: ignore[assignment]
-else:
-    HttpProtocol = None  # type: ignore[assignment]
 
-_SOCKETIO_ASYNC_MODE = "eventlet" if eventlet else "threading"
+_SOCKETIO_ASYNC_MODE = "eventlet"
 
 
 # Ensure the legacy ``Modules`` package is importable when running from the