Two host-built CodeMirror editors mounted outside the data table, each one assembled by hand
from createSqlExtensions() + buildCompletionContext(). Both
editors share the loaded table's live schema via
actions.getCompletionContext() and refresh whenever a derived column is added.
Type Ctrl/Cmd+Space
to see column names (with their DuckDB types) and DuckDB functions (with category +
description) in the dropdown.