Flag with pending draw offer

FIDE Laws of Chess 5.2
"c. The game is drawn upon agreement between the two players during the game. This
immediately ends the game. (See Article 9.1)"

That is quite clear.

On the practical issue, you should have thought for 9 seconds and then either played a move or accepted the draw.

@tpr Yes, the case of accepting before the flag is clear in both sets of rules — obviously that's a draw. Only the USCF rules are particularly clear on what happens if your flag is called before you accept (i.e., that this is a loss).

FIDE Laws of Chess
6.9 Except where one of the Articles: 5.1.a, 5.1.b, 5.2.a, 5.2.b, 5.2.c applies, if a player does
not complete the prescribed number of moves in the allotted time, the game is lost by
the player. However, the game is drawn, if the position is such that the opponent cannot
checkmate the player’s king by any possible series of legal moves.

So it is quite clear flag before accept = loss
Accept before flag = draw

@tpr As I've already said, I agree with your interpretation, but the FIDE rules are not well written. One of the listed exceptions covers draw by agreement, and then there's an entire article devoted to defining that. So there's quite a bit of rules-lawyering to be done before reaching the proper conclusion. The USCF rules explicitly call out the situation, as they should.