feat(hook): honor before_processing return value to gate chain execution

conserver/hook.py

@@ -12,15 +12,20 @@ def before_processing(
     vcon_id: str,
     chain_details: Dict[str, Any],
     context: Optional[Dict[str, Any]],
-) -> None:
+) -> Optional[str]:
     """Called before processing of a vCon starts.
 
     Args:
         vcon_id: The vCon identifier.
         chain_details: The chain configuration for this processing run.
         context: Optional context data (e.g. trace_id, span_id).
+
+    Returns:
+        The vCon identifier to continue chain processing, or a falsy value
+        (None / False / "") to skip processing for this vCon without raising
+        and without sending it to the DLQ. Mirrors the link contract.
     """
-    pass
+    return vcon_id
 
 
 def after_processing(

conserver/main.py

@@ -732,7 +732,12 @@ def _handle_vcon(
     try:
         context = context or {}
         context["ingress_list"] = ingress_list
-        hook.before_processing(vcon_id, chain_details, context)
+        if not hook.before_processing(vcon_id, chain_details, context):
+            logger.info(
+                "[%s] before_processing skipped vCon %s on ingress %s",
+                worker_name, vcon_id, ingress_list,
+            )
+            return
         vcon_chain_request.process()
     except Exception as e:
         processing_error = e