Keep the user's shift; trust the text guess less

- A tapped shift (on or off) survives the field re-reporting its context:
  it lasts until a character is typed, the hint changes or a field is focused
- An input-method reset forgets the guessed text and pending dead key, so
  double-space can't delete a character the keyboard never saw
- Fields that state typing preferences only get capitals if they ask
- Trackpad moves in fields without surrounding text make the guess unknown;
  Backspace removes a whole grapheme cluster from it

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tests/tst_shiftstate.cpp

@@ -111,6 +111,46 @@ private Q_SLOTS:
         shift.characterTyped();
         QCOMPARE(shift.mode(), Mode::Off);
     }
+
+    void repeatedHintKeepsUserShift()
+    {
+        ShiftState shift;
+        shift.setAutomatic(false);
+        shift.press(0);
+        shift.release();
+        shift.setAutomatic(false); // the field re-reported
+        QCOMPARE(shift.mode(), Mode::Once);
+    }
+
+    void repeatedHintKeepsUserUnshift()
+    {
+        ShiftState shift;
+        shift.setAutomatic(true);
+        shift.press(0); // off at a sentence start
+        shift.release();
+        shift.setAutomatic(true);
+        QCOMPARE(shift.mode(), Mode::Off);
+    }
+
+    void changedHintOverridesUserShift()
+    {
+        ShiftState shift;
+        shift.setAutomatic(true);
+        shift.press(0);
+        shift.release();
+        shift.setAutomatic(false);
+        shift.setAutomatic(true); // e.g. backspaced to a sentence start
+        QCOMPARE(shift.mode(), Mode::Once);
+    }
+
+    void hintAppliesAgainAfterTyping()
+    {
+        ShiftState shift;
+        shift.setAutomatic(true);
+        shift.characterTyped(); // e.g. a space at a sentence start
+        shift.setAutomatic(true);
+        QCOMPARE(shift.mode(), Mode::Once);
+    }
 };
 
 QTEST_GUILESS_MAIN(TestShiftState)