Four lib files and the 536-line UI flow test, into seven new files. Only
Flutter's generated windows/runner/win32_window.cpp remains, and editing
that would be undone by regeneration.
All four lib splits used part/part of first time, applying the rule
learned in focus_owner. models.dart needed a hand fix: it has a
`library;` directive, which must precede any `part`.
60 tests passing before and after. flutter analyze reports the same 4
pre-existing infos as a detached worktree at HEAD - which is how I
caught that an intermediate run's 7 issues were 3 of my own.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_011w2Pj4Ek3ZNMQVYcFHgXDY
