Enhance session management and logging configuration

- Updated .env.example to clarify audio frame size validation and default codec settings.
- Refactored logging setup in main.py to support JSON serialization based on log format configuration.
- Improved session.py to dynamically compute audio frame bytes and include protocol version in session events.
- Added tests to validate session start events and audio frame handling based on chunk size settings.

engine/app/main.py

@@ -80,18 +80,35 @@ backend_gateway = build_backend_adapter_from_settings()
 
 # Configure logging
 logger.remove()
-logger.add(
-    "./logs/active_call_{time}.log",
-    rotation="1 day",
-    retention="7 days",
-    level=settings.log_level,
-    format="{time:YYYY-MM-DD HH:mm:ss} | {level: <8} | {name}:{function}:{line} - {message}"
-)
-logger.add(
-    lambda msg: print(msg, end=""),
-    level=settings.log_level,
-    format="{time:HH:mm:ss} | {level: <8} | {message}"
-)
+_log_format = str(settings.log_format or "text").strip().lower()
+if _log_format == "json":
+    logger.add(
+        "./logs/active_call_{time}.log",
+        rotation="1 day",
+        retention="7 days",
+        level=settings.log_level,
+        serialize=True,
+        format="{message}",
+    )
+    logger.add(
+        lambda msg: print(msg, end=""),
+        level=settings.log_level,
+        serialize=True,
+        format="{message}",
+    )
+else:
+    logger.add(
+        "./logs/active_call_{time}.log",
+        rotation="1 day",
+        retention="7 days",
+        level=settings.log_level,
+        format="{time:YYYY-MM-DD HH:mm:ss} | {level: <8} | {name}:{function}:{line} - {message}",
+    )
+    logger.add(
+        lambda msg: print(msg, end=""),
+        level=settings.log_level,
+        format="{time:HH:mm:ss} | {level: <8} | {message}",
+    )
 
 
 @app.get("/health")