fix(ui): name the default button on the quit prompt

Item 31. The user could not tell which button Enter would press on the
unsynced-changes dialog.

The code was already correct: setDefaultButton() is called, and Qt agrees,
isDefault() and hasFocus() are both true on "Sync and quit". The active
style, qt6ct-style, simply draws no visible default-button decoration. The
GIMP dialog offered for comparison is GTK drawing its own focus ring, a
different toolkit.

Naming the default in the text rather than restyling the button:
overriding the appearance means fighting the user's theme, which is worse
than one word. The safe option was already the default, so no behaviour
changed.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

2 files changed, 26 insertions, 1 deletions

diff --git a/docs/superpowers/plans/2026-08-03-post-0.1.0-usability.md b/docs/superpowers/plans/2026-08-03-post-0.1.0-usability.md
index f7cf0e3..1edcf59 100644
--- a/docs/superpowers/plans/2026-08-03-post-0.1.0-usability.md
+++ b/docs/superpowers/plans/2026-08-03-post-0.1.0-usability.md
@@ -75,7 +75,7 @@ taking that too literally.
 | 28 | Re-adding `unread` counts 2 unsynced changes, not 0 | correctness | S | open |
 | 29 | Sync button stays enabled during a background sync | feedback | XS | **done** |
 | 30 | The blank right pane is wasted space | presentation | M | open |
-| 31 | The quit prompt has no highlighted default button | discoverability | XS | open, needs repro |
+| 31 | The quit prompt has no highlighted default button | discoverability | XS | **done** |
 | 32 | Esc does not blank the right pane | workflow | XS | **done** |
 | 33 | Status bar messages never expire | feedback | S | open |
 | 34 | No overview of the Maildir itself | information | M | open |
@@ -1489,6 +1489,22 @@ theme issue the item becomes a documentation note rather than a change.
 **Constraint:** whatever default is chosen must be the safe one. On a prompt
 about losing unsynced work, Enter must not fall on "Quit anyway".
 
+### Outcome (done): the code was right, the theme draws nothing
+
+Reproduced from a screenshot: it is the three-button `ask` prompt. Probed rather
+than guessed, and Qt agrees the default is set. On that dialog `isDefault()` and
+`hasFocus()` are both true on "Sync and quit", and `defaultButton()` returns it.
+
+**The active style is `qt6ct-style`, which draws no visible default-button
+decoration.** The GIMP dialog the user compared against is GTK drawing its own
+focus ring, a different toolkit, so the two are not comparable and this was never
+a qtmaildir bug.
+
+Fixed by naming the default in the button text rather than restyling it.
+Overriding a button's appearance means fighting the user's chosen theme, which
+is a worse outcome than one word. The safe option was already the default, per
+the constraint above, so no behaviour changed.
+
 ## 32. Esc does not blank the right pane
 
 **Observed (user, 2026-08-04):** "Esc in the main window should blank the right
diff --git a/src/mainwindow.cpp b/src/mainwindow.cpp
index e546af5..b62d8d7 100644
--- a/src/mainwindow.cpp
+++ b/src/mainwindow.cpp
@@ -189,6 +189,15 @@ void MainWindow::closeEvent(QCloseEvent *event)
                 box.addButton(tr("Quit anyway"), QMessageBox::DestructiveRole);
             box.addButton(QMessageBox::Cancel);
             box.setDefaultButton(sync);
+
+            // The default is set correctly and Qt agrees (isDefault() and
+            // hasFocus() are both true on it), but qt6ct-style draws no
+            // visible default-button decoration, so Enter's target is
+            // invisible on this desktop. Naming it in the text costs nothing
+            // and does not fight the theme.
+            // ponytail: text, not a styled button. Restyling the button means
+            // overriding the user's theme, which is worse than a sentence.
+            sync->setText(tr("Sync and quit (default)"));
             box.exec();
 
             if (box.clickedButton() == sync) {