Command palette: a filterable role="listbox" of role="option" commands with arrow navigation, type-to-filter (matching text + data-hl-keywords), automatic empty-state and group hiding, and Enter to run the active command (emits a cancelable hl:command CustomEvent). The filter query is observable through onValueChange/hl:change and controllable through the returned API. When the palette lives inside a <dialog>, an optional data-hl-command-hotkey opens it with Cmd/Ctrl+key.