[BUG] TicTacToe `check_block_player()` has same board corruption bug

[galpt]

Bug Description

In cog/games.py lines 293-300, the check_block_player() function has the same board corruption pattern as check_fork_opportunities().

cog/games.py#L293-L300

def check_block_player(self):
    empty = [i for i, c in enumerate(self.board) if c == " "]
    for idx in empty:
        self.board[idx] = player_mark  # <-- Corrupts board
        if self.check_winner(player_mark):
            self.board[idx] = " "  # Only resets idx
            return idx
        self.board[idx] = " "
        for i in range(self.size * self.size):
            if self.board[i] == player_mark:  # <-- Line 296: corrupts board
                continue
            self.board[i] = player_mark
            if self.check_winner(player_mark):
                self.board[i] = " "  # Resets i but...
                return idx
            self.board[i] = " "  # Only resets i on each iteration
    return None

Impact: If check_winner(player_mark) returns True at line 297, the function returns before reaching line 299's cleanup. The board is left corrupted with extra player marks.

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How to Fix

Apply the same fix - track all modified cells:

def check_block_player(self):
    empty = [i for i, c in enumerate(self.board) if c == " "]
    for idx in empty:
        self.board[idx] = player_mark
        modified = [idx]
        if self.check_winner(player_mark):
            for m in modified:
                self.board[m] = " "
            return idx
        self.board[idx] = " "
        for i in range(self.size * self.size):
            if self.board[i] == player_mark:
                continue
            self.board[i] = player_mark
            modified.append(i)
            if self.check_winner(player_mark):
                for m in modified:
                    self.board[m] = " "
                return idx
            self.board[i] = " "
    return None

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Severity

Critical - Causes incorrect bot defensive moves

[galpt]

[STILL PRESENT] check_block_player() has same board corruption risk - board state restored only on success path, not if exception occurs during check_winner().