Step 12 of the gui/app.py + gui/preview.py structural refactor — the
biggest single move out of app.py. The entire ~3020-line BooruApp
QMainWindow class moves to its own module under gui/. The class body
is byte-identical: every method, every signal connection, every
private attribute access stays exactly as it was.
main_window.py imports the helper classes that already moved out of
app.py (SearchState, LogHandler, AsyncSignals, InfoPanel) directly
from their canonical sibling modules at the top of the file, so the
bare-name lookups inside BooruApp method bodies (`SearchState(...)`,
`LogHandler(self._log_text)`, `AsyncSignals()`, `InfoPanel()`) keep
resolving to the same class objects. Same package depth as app.py
was, so no relative-import depth adjustment is needed for any of
the lazy `..core.X` or `.preview` imports inside method bodies —
they keep working through the preview.py shim until commit 14
swaps them to canonical paths.
app.py grows the BooruApp re-export shim line. After this commit
app.py is just imports + log + the four helpers (run,
_apply_windows_dark_mode, _load_user_qss, _BASE_POPOUT_OVERLAY_QSS)
+ the shim block. Commit 13 carves the helpers out, commit 14
deletes the shims and the file.
VERIFICATION: full method-cluster sweep (see docs/REFACTOR_PLAN.md
"Commit 12 expanded verification" section), not the 7-item smoke test.
