A CDP call sent after the socket closed (e.g. Steam restarting between
Runtime.enable and the first inject) waited forever, so the helper hung
instead of reconnecting. Such calls now resolve empty at once.
down:/up: were checked with MODKEY[arg], which inherited names like
constructor or toString pass (xdotool then got a junk key name). The check
is now allowedMod() in allowlist.mjs, covered by its test.
Steam sends Tab as the text "\t" and drops Shift. With Shift, Tab now
goes to the xdotool helper (shift+Tab, ISO_Left_Tab on any keymap); the
suggestions text model resets on it like on Shift+arrows. The helper's
allowlist moves to allowlist.mjs with a test (flake check
vr-keyboard-extra-keys).