A shared Bootstrap-only combobox that replaces the flat instance <select> on
Flow Debugger and Debug View (design docs/plans/2026-09-08-instance-picker-design.md,
plan task 2): a text field over a dropdown panel hosting TreeView across the
InstanceTreeBuilder forest, every area collapsed on open. Clicking an area row
toggles it, clicking an instance row selects it, closes the panel and raises
SelectedInstanceIdChanged. Outside clicks close through a transparent fixed
backdrop — the same pattern TreeView uses for its context menu, so no JavaScript.
A site change (new Areas/Instances references) closes the panel and clears the
field when the selection no longer resolves; a parent-driven SelectedInstanceId
change re-derives the field text while closed. ItemLabel customises row and field
text (Debug View wants a "(State)" suffix) while search still matches UniqueName.
TreeView gains one additive public ToggleExpanded(key) — the chevron's existing
private toggle, exposed so a consumer whose own NodeContent owns the label click
can toggle the branch.
Search filtering and keyboard handling land in task 3; _filter/Rebuild() are in
place for them.
Claude-Session: https://claude.ai/code/session_01NcMG6xXdsJbmD2wYAgkK29
Joseph Doherty