feat(gateway): DataSink.publish_reading multi-name fan-out

ingestor/io/data_sink.py

@@ -0,0 +1,39 @@
+import ingestor.metrics as metrics
+
+
+class DataSink:
+    """Gateway egress wrapper: fans a reading out to every configured name/collection.
+
+    `postgres` is unused for now — task 12 adds `update_write_status` on top of it.
+    """
+
+    def __init__(self, data_manager, postgres, metadata: dict | None = None) -> None:
+        self.data_manager = data_manager
+        self.postgres = postgres
+        self.metadata = metadata
+
+    async def emit_metric(self, **kwargs) -> None:
+        # ponytail: delegate to data_manager, it's already a SientiaMonitoring
+        await self.data_manager.emit_metric(**kwargs)
+
+    async def publish_reading(self, tag: str, value, timestamp, names: list[dict]) -> None:
+        """Publish one MongoDB document per name entry and record its tag value metric."""
+        for name in names:
+            doc = {
+                'tag': tag,
+                'name': name['tag_name'],
+                'model_id': name['model_id'],
+                'timestamp': timestamp,
+                'value': value,
+            }
+            await self.data_manager.publish(name['collection'], doc)
+            await self.emit_metric(
+                metric_object=metrics.OPC_TAG_VALUE,
+                method='set',
+                value=value,
+                tags={
+                    'pod_id': self.data_manager.pod_id,
+                    'tag_name': name['tag_name'],
+                    'model_id': name['model_id'],
+                },
+            )