Add g2048 tile spawn regression

tests/test_g2048_spawn.py

@@ -0,0 +1,89 @@
+import os
+import subprocess
+import textwrap
+
+
+def test_g2048_spawns_tile_after_full_board_merge(tmp_path):
+    fake_raylib = tmp_path / 'raylib.h'
+    fake_raylib.write_text(textwrap.dedent('''
+        typedef struct Color { unsigned char r, g, b, a; } Color;
+        #define KEY_ESCAPE 0
+        static inline void InitWindow(int width, int height, const char* title) {}
+        static inline void SetTargetFPS(int fps) {}
+        static inline int IsKeyDown(int key) { return 0; }
+        static inline void CloseWindow(void) {}
+        static inline void BeginDrawing(void) {}
+        static inline void ClearBackground(Color color) {}
+        static inline void DrawRectangle(int posX, int posY, int width, int height, Color color) {}
+        static inline void DrawText(const char* text, int posX, int posY, int fontSize, Color color) {}
+        static inline void EndDrawing(void) {}
+        static inline int IsWindowReady(void) { return 0; }
+    '''))
+
+    source = tmp_path / 'g2048_spawn_test.c'
+    source.write_text(textwrap.dedent('''
+        #include <stdio.h>
+        #include "g2048.h"
+
+        int main(void) {
+            unsigned char observations[SIZE * SIZE] = {0};
+            float actions[1] = {2.0f};  // LEFT: c_step adds 1 to action.
+            float rewards[1] = {0};
+            float terminals[1] = {0};
+
+            Game game = {0};
+            game.observations = observations;
+            game.actions = actions;
+            game.rewards = rewards;
+            game.terminals = terminals;
+            game.empty_count = 0;
+            game.grid_changed = true;
+            game.max_episode_ticks = BASE_MAX_TICKS;
+            game.rng = 1;
+
+            const unsigned char grid[SIZE][SIZE] = {
+                {1, 1, 3, 4},
+                {5, 6, 7, 8},
+                {5, 9, 10, 11},
+                {12, 13, 14, 15},
+            };
+            for (int i = 0; i < SIZE; i++) {
+                for (int j = 0; j < SIZE; j++) {
+                    game.grid[i][j] = grid[i][j];
+                }
+            }
+
+            c_step(&game);
+
+            int observed_empty = 0;
+            for (int i = 0; i < SIZE; i++) {
+                for (int j = 0; j < SIZE; j++) {
+                    observed_empty += game.grid[i][j] == EMPTY;
+                }
+            }
+
+            if (game.empty_count != 0 || observed_empty != 0) {
+                fprintf(stderr, "expected replacement spawn after merge, empty_count=%d observed_empty=%d\\n",
+                    game.empty_count, observed_empty);
+                return 1;
+            }
+            if (game.terminals[0] != 0.0f) {
+                fprintf(stderr, "test board should remain non-terminal after spawn\\n");
+                return 1;
+            }
+            return 0;
+        }
+    '''))
+
+    binary = tmp_path / 'g2048_spawn_test'
+    repo_root = os.getcwd()
+    subprocess.run([
+        os.environ.get('CC', 'cc'),
+        '-std=gnu11',
+        '-I', str(tmp_path),
+        '-I', os.path.join(repo_root, 'ocean', 'g2048'),
+        str(source),
+        '-lm',
+        '-o', str(binary),
+    ], check=True)
+    subprocess.run([str(binary)], check=True)