@bimetal/picker-headless

The canonical, framework-agnostic picker controller — instance #8 of the BIMETAL component family. Built on @bimetal/headless-core, so it shares the identity-stable getSnapshot/subscribe contract and the errors-as-state surface; the framework packages are pure bindings.

createPickerController is the family's first controller-only component: NO aggregate, NO event sourcing. Options are injected, selection is transient — because "which option is highlighted" is not a domain fact.

Single/multi select, type-to-filter, keyboard navigation, a max cap, grouped and virtualized lists, create-new, async loading, and the combobox/listbox a11y contract (aria-activedescendant, never roving focus).

The selection can also be controlled from outside: setSelection(ids) replaces it without rebuilding the picker (focus, open popup and query stay), and onSelectionChange(ids, origin) reports it with origin: 'external' — never 'user' — so a consumer can tell its own changes from user input. In multi mode, config.maxVisibleChips: n collapses everything past the first n chips into one +k marker (snapshot.visibleChips / snapshot.chipOverflow, with an accessible label naming the hidden values).

The cut line is the family's: DOM measurement and listener registration belong to the framework; every if belongs here.