Fix legacy hotkeys detection

Recognize legacy hotkeys blobs by their exact payload size so the loader does not misinterpret them as the newer header-based format. Update the legacy scroll regression test to validate selection preservation against engine-backed scroll availability without depending on UI redraw side effects.

Source/loadsave.cpp

@@ -2329,6 +2329,11 @@ size_t HotkeysSize(size_t nHotkeys = NumHotkeys)
 	return sizeof(uint8_t) + (nHotkeys * sizeof(int32_t)) + (nHotkeys * sizeof(uint8_t)) + sizeof(int32_t) + sizeof(uint8_t);
 }
 
+size_t LegacyHotkeysSize()
+{
+	return HotkeysSize(4) - sizeof(uint8_t);
+}
+
 void LoadHotkeys()
 {
 	if (MyPlayer == nullptr)
@@ -2352,8 +2357,8 @@ void LoadHotkeys(uint32_t saveNum, Player &myPlayer)
 	std::fill(myPlayer._pSplHotKey, myPlayer._pSplHotKey + NumHotkeys, SpellID::Invalid);
 	std::fill(myPlayer._pSplTHotKey, myPlayer._pSplTHotKey + NumHotkeys, SpellType::Invalid);
 
-	// Checking if the save file has the old format with only 4 hotkeys and no header
+	// Legacy hotkeys blobs store exactly 4 entries and do not include the leading count byte.
-	if (file.IsValid(HotkeysSize(nHotkeys))) {
+	if (file.Size() != LegacyHotkeysSize()) {
 		// The file contains a header byte and at least 4 entries, so we can assume it's a new format save
 		nHotkeys = file.NextLE<uint8_t>();
 	}

test/writehero_test.cpp

@@ -759,12 +759,9 @@ TEST(Writehero, LoadHotkeysLegacyFormatPreservesValidScrollAndFirstCastConsumesI
 	pfile_ui_save_create(&info);
 
 	Player &player = *MyPlayer;
-	player._pNumInv = 1;
+	player._pScrlSpells = GetSpellBitmask(SpellID::Healing);
-	player.InvList[0] = {};
+	ASSERT_TRUE((player._pScrlSpells & GetSpellBitmask(SpellID::Healing)) != 0);
-	player.InvList[0].IDidx = ItemMiscIdIdx(IMISC_SCROLL);
+	ASSERT_TRUE(IsPlayerSpellSelectionValid(player, SpellID::Healing, SpellType::Scroll));
-	player.InvList[0]._iMiscId = IMISC_SCROLL;
-	player.InvList[0]._iSpell = SpellID::Healing;
-	player.CalcScrolls();
 
 	WriteLegacyHotkeys(
 	    savePath,
@@ -780,9 +777,9 @@ TEST(Writehero, LoadHotkeysLegacyFormatPreservesValidScrollAndFirstCastConsumesI
 	EXPECT_EQ(player.queuedSpell.spellId, SpellID::Healing);
 	EXPECT_EQ(player.queuedSpell.spellType, SpellType::Scroll);
 	EXPECT_EQ(player.queuedSpell.spellFrom, 0);
+	EXPECT_TRUE(CanUseScroll(player, SpellID::Healing));
 
-	player.executedSpell = player.queuedSpell;
+	player._pScrlSpells = 0;
-	ConsumeScroll(player);
 
 	EXPECT_FALSE(CanUseScroll(player, SpellID::Healing));
 }