Send binary WebSocket frames in one write

src/web_httpd_adapter.h

@@ -26,6 +26,15 @@ void web_httpd_wipe_request(httpd_req_t *request, bool closing);
 esp_err_t web_httpd_upgrade(httpd_req_t *request,
                             esp_err_t (*handler)(httpd_req_t *));
 
+#define WEB_HTTPD_WS_BINARY_MAX_PAYLOAD 512U
+/* HTTPD-owner work only; caller retains generation/lifecycle and one-work-slot
+ * ownership. Synchronous FIN/binary/unmasked send through the session override.
+ * Non-full writes synchronously block further session sends and abort the socket;
+ * caller must retain normal failure/cleanup accounting, never replay the frame. */
+esp_err_t web_httpd_ws_send_binary(httpd_handle_t server, int fd,
+                                    const void *expected_context,
+                                    const uint8_t *payload, size_t length);
+
 /* Serialized server startup only, exact-match ordinary GET, URI <= 127 bytes.
  * Stage both allocations before publication; HTTPD owns/frees them on success. */
 esp_err_t web_httpd_register_optional_get(httpd_handle_t server, const httpd_uri_t *uri);