win: support running inside an AppContainer (lowbox token)

docs/src/misc.rst

@@ -842,6 +842,14 @@ API
 
     .. versionadded:: 1.25.0
 
+.. c:function:: int uv_os_is_app_container(void)
+
+    Returns `1` when the current process runs inside a Windows AppContainer
+    (that is, with a lowbox token), `0` otherwise. Always returns `0` on
+    platforms other than Windows.
+
+    .. versionadded:: 1.52.0
+
 .. c:function:: int uv_gettimeofday(uv_timeval64_t* tv)
 
     Cross-platform implementation of :man:`gettimeofday(2)`. The timezone

include/uv.h

@@ -1394,6 +1394,8 @@ UV_EXTERN int uv_os_gethostname(char* buffer, size_t* size);
 
 UV_EXTERN int uv_os_uname(uv_utsname_t* buffer);
 
+UV_EXTERN int uv_os_is_app_container(void);
+
 struct uv_metrics_s {
   uint64_t loop_count;
   uint64_t events;

src/unix/core.c

@@ -1869,6 +1869,11 @@ int uv_os_uname(uv_utsname_t* buffer) {
   return r;
 }
 
+int uv_os_is_app_container(void) {
+  /* AppContainers are a Windows concept. */
+  return 0;
+}
+
 int uv__getsockpeername(const uv_handle_t* handle,
                         uv__peersockfunc func,
                         struct sockaddr* name,