midiviz: t shows the window again — visibility is witnessed before the flag change

Qt hides the window the instant setWindowFlag runs; the re-show guard ran
after the call and always read False, so t dismissed the lens for good
(PLN: 'it does kill it, risky'). The check now happens before.

tools/bridge/midiviz.py

@@ -3029,16 +3029,18 @@ def build_widget(port_label: str, reader: "Reader | None", scale: float = 1.0,
         def _set_on_top(self, on: bool):
             self.on_top = on
             self._sync_menu()
-            # Qt requires the window be re-shown after a flag change for the
-            # compositor to be told. It does not touch the KWin all-desktops
-            # rule, which is keyed on the app id and stays in force.
+            # PLN, 2026-09-24: "pressing t makes the win disappear and never
+            # reappear it does kill it". The cause is an ordering trap: Qt
+            # HIDES the window the instant setWindowFlag runs, so the old
+            # `if self.isVisible(): self.show()` — written after the call —
+            # always read False and the re-show never fired. Visibility must
+            # be captured BEFORE the flag change: it is the only witness of
+            # whether the window was on screen. Qt requires the re-show after
+            # a flag change for the compositor to be told; it does not touch
+            # the KWin all-desktops rule, which is keyed on the app id.
+            was_visible = self.isVisible()
             self.setWindowFlag(Qt.WindowType.WindowStaysOnTopHint, on)
-            # Only re-show a window that was already on screen. Qt needs the
-            # re-show to tell the compositor about a flag change on a VISIBLE
-            # window; a hidden one picks the flag up on its next show() -- and
-            # toggling the pin from the tray must not be a way to un-hide the
-            # lens PLN just dismissed.
-            if self.isVisible():
+            if was_visible:
                 self.show()
             self.update()