Typing in the field is the filter: the forest is rebuilt to the matching
instances plus their ancestor areas and force-expanded so every match is on
screen; clearing the text restores the full forest, collapsed. Both bulk
expansions are deferred to OnAfterRenderAsync, because the TreeView only exists
once the panel has rendered.
Enter picks the first instance the operator can actually SEE — document order,
descending into a branch only when the tree reports it expanded — so with areas
collapsed it picks the first root instance, and with a filter (every branch
expanded) it degrades to plain document order. Escape closes and restores the
field text from the current selection; ArrowDown hands keyboard navigation to
the tree via a new additive TreeView.FocusFirstVisibleAsync(), which reuses the
existing roving-tabindex _focusNeedsApply path rather than adding a second
focus mechanism.
No preventDefault: Blazor's flag is all-or-nothing per element, and neither
default is harmful (Enter in a text input outside a form does nothing,
ArrowDown just moves the caret) while suppressing Tab would trap the control.
Claude-Session: https://claude.ai/code/session_01NcMG6xXdsJbmD2wYAgkK29
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