chore: Update OpenAPI spec from LangGraph API v0.4.0 (#6011)

This PR updates the OpenAPI specification with changes detected from the
LangGraph API server.

**Changes detected as of LangGraph API version 0.4.0**

This update was automatically generated by the sync workflow in the
langgraph-api repository.

Co-authored-by: hinthornw <hinthornw@users.noreply.github.com>

docs/docs/cloud/reference/api/openapi.json

@@ -1520,6 +1520,73 @@
         }
       }
     },
+    "/threads/{thread_id}/stream": {
+      "get": {
+        "tags": [
+          "Threads"
+        ],
+        "summary": "Join Thread Stream",
+        "description": "This endpoint streams output in real-time from a thread. The stream will include the output of each run executed sequentially on the thread and will remain open indefinitely. It is the responsibility of the calling client to close the connection.",
+        "operationId": "join_thread_stream_threads__thread_id__stream_get",
+        "parameters": [
+          {
+            "description": "The ID of the thread.",
+            "required": true,
+            "schema": {
+              "type": "string",
+              "format": "uuid",
+              "title": "Thread Id",
+              "description": "The ID of the thread."
+            },
+            "name": "thread_id",
+            "in": "path"
+          },
+          {
+            "required": false,
+            "schema": {
+              "type": "string",
+              "title": "Last Event ID",
+              "description": "The ID of the last event received. Used to resume streaming from a specific point. Pass '-' to resume from the beginning."
+            },
+            "name": "Last-Event-ID",
+            "in": "header"
+          }
+        ],
+        "responses": {
+          "200": {
+            "description": "Success",
+            "content": {
+              "text/event-stream": {
+                "schema": {
+                  "type": "string",
+                  "description": "The server will send a stream of events in SSE format.\n\n**Example event**:\n\nid: 1\n\nevent: message\n\ndata: {}"
+                }
+              }
+            }
+          },
+          "404": {
+            "description": "Not Found",
+            "content": {
+              "application/json": {
+                "schema": {
+                  "$ref": "#/components/schemas/ErrorResponse"
+                }
+              }
+            }
+          },
+          "422": {
+            "description": "Validation Error",
+            "content": {
+              "application/json": {
+                "schema": {
+                  "$ref": "#/components/schemas/ErrorResponse"
+                }
+              }
+            }
+          }
+        }
+      }
+    },
     "/threads/{thread_id}/runs": {
       "get": {
         "tags": [