feat: add temporary hazardous barriers in hard mode

include/consts.h

@@ -1,6 +1,7 @@
 #ifndef CONSTS_H
 #define CONSTS_H
-#endif
+
+#include <cstdint>
 
 const int START_LENGTH = 4;
 const int START_LENGTH_HARD = 2;
@@ -14,9 +15,36 @@ const uint16_t CURSE_PAL_GLOW    = 18;
 const uint16_t CURSE_PAL_CORE    = 19;
 const uint16_t CURSE_PAL_LEAF    = 20;
 
+// Barrier palette indices in SPRITE_PALETTE_SUB (animated every VBlank)
+const uint16_t BARRIER_PAL_EDGE   = 21;
+const uint16_t BARRIER_PAL_FILL   = 22;
+const uint16_t BARRIER_PAL_STRIPE = 23;
+const uint16_t BARRIER_PAL_WARN   = 24;
+
+// Hard-mode temporary fatal barriers (all timings in 60 Hz VBlank frames,
+// so they stay constant in wall-clock time while the tick rate accelerates)
+const int BARRIER_START_APPLES          = 3;   // Barriers only start appearing after eating a few apples
+const int BARRIER_MULTI_SPAWN_APPLES_2  = 16;  // Apples required to spawn up to 2 barriers at once
+const int BARRIER_MULTI_SPAWN_APPLES_3  = 30;  // Apples required to spawn up to 3 barriers at once
+const int BARRIER_MAX_COUNT             = 4;   // Max simultaneous barriers (reached at SPEED_APPLES_CAP)
+const int BARRIER_MIN_LENGTH         = 2;
+const int BARRIER_BASE_MAX_LENGTH    = 4;   // Max length when barriers first appear
+const int BARRIER_MAX_LENGTH         = 10;  // Max length later in the game (reached at SPEED_APPLES_CAP)
+const int BARRIER_OAM_SLOTS          = BARRIER_MAX_COUNT * BARRIER_MAX_LENGTH; // Reserved OAM ids 0..39
+const int BARRIER_WARN_FRAMES        = 120; // 2.0 s flashing announcement (harmless)
+const int BARRIER_SOLIDIFY_FRAMES    = 20;  // Last part of warning: flickers to solid look
+const int BARRIER_ACTIVE_FRAMES      = 240; // 4.0 s fatal phase
+const int BARRIER_FADE_FRAMES        = 45;  // Last part of active phase: slow blink (still fatal)
+const int BARRIER_FIRST_SPAWN_FRAMES = 180; // 3.0 s grace period after reaching BARRIER_START_APPLES
+const int BARRIER_INTERVAL_MAX_FRAMES = 540; // 9.0 s between spawns at BARRIER_START_APPLES
+const int BARRIER_INTERVAL_MIN_FRAMES = 120; // 2.0 s between spawns at SPEED_APPLES_CAP
+const int BARRIER_INTERVAL_JITTER    = 60;  // Random 0..1 s extra delay
+const int BARRIER_RETRY_FRAMES       = 30;  // Retry delay if no valid spot was found
+const int BARRIER_HEAD_SAFE_DISTANCE = 5;   // Min wrapped Manhattan distance from the snake head
+
 // Speed scaling configuration (gradual acceleration based on consumed apples)
 const int SPEED_BASE_NORMAL_MHZ = 5000;  // 5.0 Hz (~200 ms per step)
-const int SPEED_BASE_HARD_MHZ   = 9000;  // 9.0 Hz (~111 ms per step)
+const int SPEED_BASE_HARD_MHZ   = 5000;  // 5.0 Hz: hard mode starts as slow as normal mode
 const int SPEED_MAX_NORMAL_MHZ  = 13000; // 13.0 Hz (~77 ms per step)
 const int SPEED_MAX_HARD_MHZ    = 17000; // 17.0 Hz (~59 ms per step)
 const int SPEED_APPLES_CAP      = 40;    // Apples consumed to reach max intensity & speed
@@ -69,4 +97,6 @@ const char BITMAP_SEGMENT[] = {
         5,6,6,6,6,6,6,5,
         5,6,6,6,6,6,6,5,
         0,5,5,5,5,5,5,0
-	};
+	};
+
+#endif // CONSTS_H