Fix MCP send_http_request ignoring environmentId (#654)

plugins-external/mcp-server/README.md

@@ -33,3 +33,26 @@ Restart Claude Desktop and make sure Yaak is running.
 - `get_environment_id` - Get the current environment ID
 - `copy_to_clipboard` - Copy text to the system clipboard
 - `show_toast` - Show a toast notification in Yaak
+
+## Environment Selection
+
+`send_http_request` accepts an optional `environmentId` for that execution. It overrides the
+active environment without changing the selection in Yaak. Omitting it uses the host's
+active environment, as before.
+
+The ID must identify a base or sub-environment in the request's workspace. An empty,
+unknown, foreign-workspace, or folder environment ID returns an error before sending.
+Use the base environment ID to run with global variables only. Folder variables still
+apply according to the request's folder hierarchy.
+
+```json
+{
+  "id": "rq_example",
+  "workspaceId": "wk_example",
+  "environmentId": "ev_staging"
+}
+```
+
+This requires a Yaak host with support for the `environmentId` plugin API field;
+older hosts ignore it. `get_environment_id` reports the active selection, not the
+override used by a previous send.