From c70a19b8c16be38a66e53eb54edd2fd1a106fba5 Mon Sep 17 00:00:00 2001
From: Byte <byte@coreyja.com>
Date: Tue, 14 Jul 2026 22:32:11 -0400
Subject: [PATCH] fix: spawn food each turn in live games

The live game loop (game_runner -> apply_turn) never called
rules::food::maybe_spawn_food -- it was only wired into the
run_game_with_random_moves simulation helper. Live games advertised
food_spawn_chance=15 / minimum_food=1 on the wire but no food ever
spawned after the initial board (confirmed in prod: game 54be71a6 had
5 food at turn 0 and zero from ~turn 30 onward).

Add engine::spawn_food, called by the game runner after each turn and
before the frame is recorded so the viewer and the snakes' next /move
requests both see the new food. Constrictor games (in-flight PR #128)
never spawn food, so the helper is mode-aware from the start.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
---
 server/src/engine/mod.rs  | 46 +++++++++++++++++++++++++++++++++++++++
 server/src/game_runner.rs |  3 +++
 2 files changed, 49 insertions(+)

diff --git a/server/src/engine/mod.rs b/server/src/engine/mod.rs
index c8fa953..8dd21b8 100644
--- a/server/src/engine/mod.rs
+++ b/server/src/engine/mod.rs
@@ -250,6 +250,20 @@ pub fn apply_turn(game: &mut EngineGame, moves: &[(String, Direction)]) {
     }
 }
 
+/// Spawn food for the next turn in modes that spawn food.
+///
+/// Food spawning lives outside the per-turn rules pipeline (matching the Go
+/// engine, where the game loop spawns food between turns), so every caller of
+/// `apply_turn` must also call this. Constrictor games never spawn food; all
+/// other modes use the standard chance/minimum settings.
+pub fn spawn_food(game: &mut EngineGame) {
+    if game.meta.ruleset_name == "constrictor" {
+        return;
+    }
+    let mut rng = rand::thread_rng();
+    rules::food::maybe_spawn_food(&mut rng, &mut game.board, &game.meta.settings);
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;
@@ -1275,6 +1289,38 @@ mod tests {
         }
     }
 
+    #[test]
+    fn test_spawn_food_standard_respects_minimum_food() {
+        let mut game = create_test_game(2);
+        game.board.food.clear();
+
+        spawn_food(&mut game);
+
+        // minimum_food is 1, so an empty board must get food back.
+        assert!(
+            !game.board.food.is_empty(),
+            "standard games must respawn food up to minimum_food"
+        );
+    }
+
+    #[test]
+    fn test_spawn_food_constrictor_never_spawns() {
+        let mut game = create_test_game(2);
+        game.meta.ruleset_name = "constrictor".to_string();
+        game.board.food.clear();
+
+        // food_spawn_chance is probabilistic; run enough iterations that a
+        // broken guard would virtually always spawn at least once.
+        for _ in 0..100 {
+            spawn_food(&mut game);
+        }
+
+        assert!(
+            game.board.food.is_empty(),
+            "constrictor games must never spawn food"
+        );
+    }
+
     /// Test that create_initial_game assigns unique IDs when the same battlesnake
     /// appears multiple times (duplicate snakes in a game)
     #[test]
diff --git a/server/src/game_runner.rs b/server/src/game_runner.rs
index b806611..c35a697 100644
--- a/server/src/game_runner.rs
+++ b/server/src/game_runner.rs
@@ -236,6 +236,9 @@ pub async fn run_game(app_state: &AppState, game_id: Uuid) -> cja::Result<()> {
         // Apply the moves using the engine
         crate::engine::apply_turn(&mut engine_game, &moves);
         engine_game.board.turn += 1;
+        // Spawn food for the next turn before the frame is recorded, so the
+        // viewer and the snakes' next /move requests both see it.
+        crate::engine::spawn_food(&mut engine_game);
 
         // Track newly eliminated snakes
         for snake in &engine_game.board.snakes {