feat: add push_dag and get_dag methods to SiloClient

- push_dag(part_number, revision_number, nodes, edges): PUT /api/items/{pn}/dag
- get_dag(part_number, revision_number=None): GET /api/items/{pn}/dag

Closes kindred/create#215

silo_client/__init__.py

@@ -902,3 +902,42 @@ class SiloClient:
         self, ods_bytes: bytes, filename: str = "sheet.ods"
     ) -> Dict[str, Any]:
         return self._upload_ods("/sheets/diff", ods_bytes, filename)
+
+    # -- DAG (feature tree) -------------------------------------------------
+
+    def push_dag(
+        self,
+        part_number: str,
+        revision_number: int,
+        nodes: List[Dict[str, Any]],
+        edges: List[Dict[str, Any]],
+    ) -> Dict[str, Any]:
+        """Push a feature DAG to the server.
+
+        Calls ``PUT /api/items/{partNumber}/dag`` with the payload
+        described in ``MULTI_USER_CLIENT.md`` Section 2.
+        """
+        pn = urllib.parse.quote(part_number, safe="")
+        return self._request(
+            "PUT",
+            f"/items/{pn}/dag",
+            {
+                "revision_number": revision_number,
+                "nodes": nodes,
+                "edges": edges,
+            },
+        )
+
+    def get_dag(
+        self, part_number: str, revision_number: Optional[int] = None
+    ) -> Dict[str, Any]:
+        """Fetch the stored DAG for an item.
+
+        Calls ``GET /api/items/{partNumber}/dag``, optionally filtered
+        by *revision_number*.
+        """
+        pn = urllib.parse.quote(part_number, safe="")
+        path = f"/items/{pn}/dag"
+        if revision_number is not None:
+            path += f"?revision={revision_number}"
+        return self._request("GET", path)