fix(matchdata): don't award a 1v1 win to a player who reported a loss

GenOnlineService/Database/Database.MatchHistory.cs

@@ -518,6 +518,76 @@ public static async Task<ulong> CreatePlaceholderMatchHistory(
 			}
 		}
 
+		/// <summary>
+		/// 1v1 tie-break used when no slot reported a win.
+		///
+		/// A player who stayed connected and reported won=false has explicitly conceded, and must not be
+		/// handed the win merely because they left the lobby last. If exactly one of the two players has an
+		/// in-game disconnect record, that player is the only one who *could not* report, and their opponent
+		/// has already declared the loss — so the disconnected player won, and there is nothing to guess.
+		///
+		/// Deliberately 1v1 only: with teams or FFA a single disconnect says nothing about who won, so those
+		/// shapes fall through to the timestamp fallback unchanged.
+		/// </summary>
+		/// <returns>TRUE when the rule decided the match; FALSE otherwise, with strReason saying why not.</returns>
+		public static bool TryResolveOneVsOneByDisconnect(
+			IReadOnlyDictionary<int, MatchdataMemberModel> members,
+			IEnumerable<Int64> disconnectedUserIDs,
+			out int winningSlotIndex,
+			out Int64 winningUserID,
+			out Int64 concedingUserID,
+			out string strReason)
+		{
+			winningSlotIndex = -1;
+			winningUserID = -1;
+			concedingUserID = -1;
+
+			// Observers and AI/placeholder slots (user_id <= 0) never quit the game, so they are not
+			// participants for this purpose - the same filter the timestamp fallback applies.
+			List<int> lstActiveSlots = new();
+			foreach (var member in members)
+			{
+				if (member.Value.side != Constants.OBSERVER_SIDE_VALUE && member.Value.user_id > 0)
+				{
+					lstActiveSlots.Add(member.Key);
+				}
+			}
+
+			if (lstActiveSlots.Count != 2)
+			{
+				strReason = $"not a 1v1 ({lstActiveSlots.Count} active participants)";
+				return false;
+			}
+
+			// Materialize once - the caller passes ConcurrentDictionary.Keys, tests pass arrays
+			List<Int64> lstDisconnectedUserIDs = disconnectedUserIDs.ToList();
+
+			List<int> lstDisconnectedSlots = new();
+			foreach (int slotIndex in lstActiveSlots)
+			{
+				if (lstDisconnectedUserIDs.Contains(members[slotIndex].user_id))
+				{
+					lstDisconnectedSlots.Add(slotIndex);
+				}
+			}
+
+			if (lstDisconnectedSlots.Count != 1)
+			{
+				strReason = $"{lstDisconnectedSlots.Count} of 2 players have an in-game disconnect record (needs exactly 1)";
+				return false;
+			}
+
+			// Exactly two active slots, so the one that is not the winner is the conceding player
+			winningSlotIndex = lstDisconnectedSlots[0];
+			int concedingSlotIndex = (lstActiveSlots[0] == winningSlotIndex) ? lstActiveSlots[1] : lstActiveSlots[0];
+
+			winningUserID = members[winningSlotIndex].user_id;
+			concedingUserID = members[concedingSlotIndex].user_id;
+			strReason = $"user={winningUserID} disconnected in-game, user={concedingUserID} stayed connected and reported won=false";
+
+			return true;
+		}
+
 		public static async Task DetermineLobbyWinnerIfNotPresent(
 	AppDbContext db,
 	GenOnlineService.Lobby lobby)
@@ -613,6 +683,27 @@ public static async Task DetermineLobbyWinnerIfNotPresent(
 					Console.WriteLine($"[WinnerDet]   IngameAbandon: user={_kv.Key} at={_kv.Value:O}");
 				foreach (var _kv in lobby.TimeMemberLeft)
 					Console.WriteLine($"[WinnerDet]   MemberLeft:    user={_kv.Key} at={_kv.Value:O}");
+				// 6a. 1v1 special case - see TryResolveOneVsOneByDisconnect for the reasoning
+				if (TryResolveOneVsOneByDisconnect(members, lobby.TimePlayerAbandonedIngame.Keys,
+						out int oneVsOneWinningSlot, out Int64 oneVsOneWinningUserID, out _, out string strOneVsOneReason))
+				{
+					Console.WriteLine($"[WinnerDet] Match={lobby.MatchID}: 1v1 disconnect rule — {strOneVsOneReason} → awarding to user={oneVsOneWinningUserID} slot={oneVsOneWinningSlot} (skipping last-to-leave fallback).");
+
+					foreach (var kv in members)
+					{
+						if (kv.Value.side == Constants.OBSERVER_SIDE_VALUE)
+							continue;
+
+						bool bIsWinner = kv.Key == oneVsOneWinningSlot;
+						Console.WriteLine($"[WinnerDet] Match={lobby.MatchID}: marking slot={kv.Key} user={kv.Value.user_id} as {(bIsWinner ? "WINNER" : "loser")}.");
+						await UpdateMatchHistorySetWinFlag(db, lobby.MatchID, kv.Key, bIsWinner);
+					}
+
+					return;
+				}
+
+				Console.WriteLine($"[WinnerDet] Match={lobby.MatchID}: 1v1 disconnect rule declined — {strOneVsOneReason}; using last-to-leave fallback.");
+
 				DateTime latestLeave = DateTime.MinValue;
 				MatchdataMemberModel? lastPlayerNullable = null;
 				int lastSlot = -1;