First step of separating business logic from the TUI. The export command built
the CSV/ODS file inside its lambda, mixed with Print/ShowError/dialog calls.
Move all of it — CSV + ODS building, sheet-name sanitising, file writing — into
src/app/export.{hpp,cpp} (namespace app, no FTXUI/console dependency):
export_connections(const System*, path, format) -> ExportResult. The TUI
command is now a thin wrapper (resolve args/dialog, call the core, render). The
core is unit-tested without any UI (test_export); 342 assertions pass.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
François
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