Is it normal for Fairy-Stockfish (janggimodern variant) to output a “pass” move like f10f10 — or even resign when the position is hopeless?

[SeongKwan]

🧾 Body

Hello,

I’m using Fairy-Stockfish with the janggimodern (Korean Chess modern rules) variant.
While testing with the following setup:

position fen 1b1aak2r/7R1/3n2c2/1p1n1p3/2P6/3R5/4BPP1P/2cNC1N2/1r1AK4/5A3 b - - 0 20 go depth 4 movetime 2553

I noticed that the engine sometimes outputs a “pass” move, for example:
bestmove f10f10 ponder d5c5

In Janggi, a pass means that the king (the royal piece) does not move —
for example, f10f10 would represent the king choosing not to move this turn.

My questions are:

1. Is this behavior intended or allowed in the janggimodern variant implementation?
   Does Fairy-Stockfish internally treat f10f10 as a legal “pass” move for the king?
   Or could this be a fallback situation (e.g. no legal move or evaluation anomaly)?

2. In some cases, when the position is extremely unfavorable,
   could the engine possibly output a “resignation” or equivalent value instead of a move?
   If so, what kind of value or UCI response should I expect when that happens —
   for example, would it return bestmove (none) or a specific score indicator?

---

🧩 Engine Log Example (for reference)

📍 Position command:
position fen 1b1aak2r/7R1/3n2c2/1p1n1p3/2P6/3R5/4BPP1P/2cNC1N2/1r1AK4/5A3 b - - 0 20

▶️ Start calculation command:
go depth 4 movetime 2553

📊 info string classical evaluation enabled
📊 info depth 1 seldepth 1 multipv 1 score cp 461 nodes 187 nps 46750 tbhits 0 time 4 pv g8g3
📊 info depth 2 seldepth 2 multipv 1 score cp 500 nodes 383 nps 63833 tbhits 0 time 6 pv g8g3 e2e2 i10i4
📊 info depth 3 seldepth 3 multipv 1 score cp 492 nodes 619 nps 68777 tbhits 0 time 9 pv g8g3 e2e2 b2a2
📊 info depth 4 seldepth 4 multipv 1 score cp 853 nodes 2495 nps 59404 tbhits 0 time 42 pv f10f10

🎯 Engine response:
bestmove f10f10 ponder d5c5

Summary:
• Variant: janggimodern
• Side to move: Black
• Depth: 4
• Evaluation: +853 cp (very favorable for side to move)
• Bestmove: f10f10 (interpreted as a pass move)
• Ponder: d5c5

---

Any clarification on how Fairy-Stockfish handles pass moves and possible resignation logic in Janggi would be greatly appreciated.

Thank you!

[ianfab]

Yes, passing is allowed, so I do not see anything wrong here. Resignation does not exist in the UCI protocol.

[SeongKwan]

Thanks a lot for your answer! That clears it up. 👍🏻👍🏻👍🏻