🦺(backend) strengthen API validation for recording options

Improve validation of parameters accepted when starting a
recording to prevent unsupported or unexpected values.

Language validation will be further tightened to only accept
languages supported by the transcribe microservice.

Add extensive API validation tests to cover these scenarios.

src/backend/core/api/serializers.py

@@ -1,6 +1,7 @@
 """Client serializers for the Meet core app."""
 
 # pylint: disable=abstract-method,no-name-in-module
+from typing import Literal
 
 from django.conf import settings
 from django.core.exceptions import SuspiciousOperation
@@ -204,6 +205,27 @@ class BaseValidationOnlySerializer(serializers.Serializer):
         raise NotImplementedError(f"{self.__class__.__name__} is validation-only")
 
 
+class RecordingOptions(BaseModel):
+    """Configuration options for recording.
+
+    Attributes:
+        language: ISO 639-1 language code compatible with whisperX.
+            When `None`, the transcription engine will attempt to
+            auto-detect the spoken language.
+        transcribe: Whether to transcribe the recorded audio.
+            When `None`, falls back to the application default.
+        original_mode: The original recording mode before any override.
+            Must be one of the valid RecordingModeChoices values when provided.
+
+    """
+
+    language: str | None = None
+    transcribe: bool | None = None
+    original_mode: Literal["screen_recording", "transcript"] | None = None
+
+    model_config = {"extra": "forbid"}
+
+
 class StartRecordingSerializer(BaseValidationOnlySerializer):
     """Validate start recording requests."""
 
@@ -216,10 +238,11 @@ class StartRecordingSerializer(BaseValidationOnlySerializer):
             "screen_recording or transcript.",
         },
     )
-    options = serializers.JSONField(
+    options = SchemaField(
+        schema=RecordingOptions | None,
         required=False,
         allow_null=True,
-        default=dict,
+        help_text="Recording options",
     )
 
 

src/backend/core/api/viewsets.py

@@ -296,12 +296,14 @@ class RoomViewSet(
             )
 
         mode = serializer.validated_data["mode"]
-        options = serializer.validated_data["options"]
+        options = serializer.validated_data.get("options")
         room = self.get_object()
 
         # May raise exception if an active or initiated recording already exist for the room
         recording = models.Recording.objects.create(
-            room=room, mode=mode, options=options
+            room=room,
+            mode=mode,
+            options=options.model_dump(exclude_none=True) if options else {},
         )
 
         models.RecordingAccess.objects.create(