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_controller.cpp

@@ -150,6 +150,46 @@ private Q_SLOTS:
         QCOMPARE(controller->shiftMode(), KeyboardController::ShiftMode::Once);
     }
 
+    void fieldHintsCanOptOutOfCapitalization()
+    {
+        TextContext context = Field;
+        context.hints = TextContext::AutoCompletion; // states preferences, no capitals among them
+        controller->setContext(context);
+        QCOMPARE(controller->shiftMode(), KeyboardController::ShiftMode::Off);
+        context.hints |= TextContext::AutoCapitalization;
+        controller->setContext(context);
+        QCOMPARE(controller->shiftMode(), KeyboardController::ShiftMode::Once);
+    }
+
+    void cursorMovesForgetTheGuessedText()
+    {
+        controller->resetContext(Field); // reports no text: we only know what we typed
+        for (const char *c : {"h", "i", "."})
+            tap(makeKey(KeyType::Character, QString::fromLatin1(c)));
+        controller->moveCursor({-2, 0}); // now somewhere inside "Hi."
+        tap(makeKey(KeyType::Space));
+        QCOMPARE(controller->shiftMode(), KeyboardController::ShiftMode::Off);
+    }
+
+    void contextReportKeepsTappedShift()
+    {
+        tap(makeKey(KeyType::Shift));
+        controller->setContext(MidSentence); // unchanged text, re-reported
+        tap(makeKey(KeyType::Character, u"a"_s));
+        QCOMPARE(engine.output, u"A");
+    }
+
+    void resetForgetsTextBefore()
+    {
+        TextContext context = MidSentence;
+        context.textBeforeCursor = u"word "_s;
+        controller->setContext(context);
+        controller->setContext(Field); // input-method reset: no surrounding text
+        tap(makeKey(KeyType::Space));
+        QCOMPARE(engine.output, u" ");
+        QCOMPARE(engine.mismatchedReplacements, 0);
+    }
+
     void doubleSpacePeriodCanBeTurnedOff()
     {
         controller->setOptions({.doubleSpacePeriod = false});

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)

tests/tst_textrules.cpp

@@ -44,6 +44,9 @@ private Q_SLOTS:
     {
         QCOMPARE(TextRules::withoutLastCharacter(u"ab"_s), u"a");
         QCOMPARE(TextRules::withoutLastCharacter(u"a👍"_s), u"a");
+        QCOMPARE(TextRules::withoutLastCharacter(u"ae\u0301"_s), u"a"); // e + combining acute
+        QCOMPARE(TextRules::withoutLastCharacter(u"a👍🏽"_s), u"a"); // with a skin tone
+        QCOMPARE(TextRules::withoutLastCharacter(QString()), QString());
         QCOMPARE(TextRules::withoutLastWord(u"one two  "_s), u"one ");
         QCOMPARE(TextRules::withoutLastWord(u"one"_s), QString());
     }