feat(gauntlet): shrink arena per phase 20x20 -> 18x18 -> 7x7; sticky cells block movement

scripts/managers/gauntlet_manager.gd

@@ -340,9 +340,12 @@ func _start_phase(phase: Phase) -> void:
 	var phase_name = _phase_to_string(phase)
 	print("[Gauntlet] Phase changed to: ", phase_name)
 	
-	if _can_rpc():
+	if _can_rpc() and multiplayer.is_server():
 		rpc("sync_phase", int(phase), phase_name)
 	
+	# Update phase explicitly with setup_arena
+	_shrink_arena()
+	
 	emit_signal("phase_changed", int(phase), phase_name)
 
 func _phase_to_string(phase: Phase) -> String:
@@ -361,6 +364,14 @@ func sync_phase(phase_index: int, phase_name: String) -> void:
 	if not is_active:
 		activate_client_side()
 	current_phase = phase_index as Phase
+	if not multiplayer.is_server():
+		var bounds = get_arena_bounds()
+		for x in range(ARENA_COLUMNS):
+			for z in range(ARENA_ROWS):
+				var pos = Vector2i(x, z)
+				if pos.x <= bounds.min or pos.x >= bounds.max or pos.y <= bounds.min or pos.y >= bounds.max:
+					if not sticky_cells.has(pos):
+						sticky_cells[pos] = true
 	_update_hud_phase(phase_name)
 
 # =============================================================================
@@ -419,11 +430,12 @@ func _apply_arena_setup() -> void:
 				continue
 			
 			# Boundary walls: perimeter (row 0, row 19, col 0, col 19)
-			if x == 0 or x == ARENA_COLUMNS - 1 or z == 0 or z == ARENA_ROWS - 1:
+			if pos.x <= 0 or pos.x >= 19 or pos.y <= 0 or pos.y >= 19:
 				# Also make border walls visually walkable floors instead of red blocks
 				gridmap.set_cell_item(Vector3i(x, 0, z), TILE_WALKABLE)
 				gridmap.set_cell_item(Vector3i(x, 1, z), -1)
-				gridmap.set_cell_item(Vector3i(x, 2, z), -1)
+				gridmap.set_cell_item(Vector3i(x, 2, z), TILE_STICKY)
+				sticky_cells[pos] = true
 				continue
 			
 			# Interior: walkable floor
@@ -1065,9 +1077,12 @@ func is_cleansed_cell(pos: Vector2i) -> bool:
 
 func cell_state(pos: Vector2i) -> CellState:
 	"""Logical state of a playable cell (v2 ground-growth model)."""
+	var b = get_arena_bounds()
+	if pos.x <= b.min or pos.x >= b.max or pos.y <= b.min or pos.y >= b.max:
+		return CellState.STICKY
 	if _is_npc_zone(pos) or _is_boundary(pos):
 		return CellState.BLOCKED
-	if sticky_cells.has(pos):
+	if is_sticky_cell(pos):
 		return CellState.STICKY
 	if cleansed_cells.has(pos):
 		return CellState.CLEANSED
@@ -1091,8 +1106,37 @@ func _tick_cleansed_cells(delta: float) -> void:
 	for pos in expired:
 		cleansed_cells.erase(pos)
 
+func get_arena_bounds() -> Dictionary:
+	match current_phase:
+		Phase.OPEN_ARENA:
+			return {"min": 0, "max": 19} # 20x20
+		Phase.ROUTE_PRESSURE:
+			return {"min": 1, "max": 18} # 18x18
+		Phase.SURVIVAL_ENDGAME:
+			return {"min": 6, "max": 12} # 7x7
+	return {"min": 0, "max": 19}
+
+func _shrink_arena() -> void:
+	if not multiplayer.is_server(): return
+	var b = get_arena_bounds()
+	var new_sticky = []
+	for x in range(ARENA_COLUMNS):
+		for z in range(ARENA_ROWS):
+			var pos = Vector2i(x, z)
+			if _is_npc_zone(pos) or _is_boundary(pos):
+				continue
+			if pos.x <= b.min or pos.x >= b.max or pos.y <= b.min or pos.y >= b.max:
+				if not sticky_cells.has(pos):
+					new_sticky.append(pos)
+	
+	if new_sticky.size() > 0:
+		if _can_rpc() and multiplayer.is_server():
+			rpc("sync_growth_apply", new_sticky)
+		else:
+			sync_growth_apply(new_sticky)
+
 func _is_boundary(pos: Vector2i) -> bool:
-	return pos.x == 0 or pos.x == ARENA_COLUMNS - 1 or pos.y == 0 or pos.y == ARENA_ROWS - 1
+	return pos.x <= 0 or pos.x >= ARENA_COLUMNS - 1 or pos.y <= 0 or pos.y >= ARENA_ROWS - 1
 
 # =============================================================================
 # Coverage tracking (v2 target: 70-75%, down from v1's 80%)
@@ -1103,12 +1147,15 @@ const COVERAGE_TARGET_MAX: float = 0.75
 
 func playable_cell_count() -> int:
 	"""Number of cells that can ever become sticky (interior, minus NPC zone)."""
+	var b = get_arena_bounds()
 	var count := 0
 	for x in range(ARENA_COLUMNS):
 		for z in range(ARENA_ROWS):
 			var pos := Vector2i(x, z)
 			if _is_boundary(pos) or _is_npc_zone(pos):
 				continue
+			if pos.x <= b.min or pos.x >= b.max or pos.y <= b.min or pos.y >= b.max:
+				continue
 			count += 1
 	return count
 
@@ -1132,6 +1179,9 @@ const FORCED_TRAP_WINDOW: float = 30.0 # final seconds where trapping is allowed
 
 func _is_cell_passable(pos: Vector2i, extra_sticky: Dictionary = {}) -> bool:
 	"""Can a player stand on / move through this cell, given a hypothetical sticky set?"""
+	var b = get_arena_bounds()
+	if pos.x <= b.min or pos.x >= b.max or pos.y <= b.min or pos.y >= b.max:
+		return false
 	if _is_boundary(pos) or _is_npc_zone(pos):
 		return false
 	if sticky_cells.has(pos) or extra_sticky.has(pos):
@@ -1390,15 +1440,21 @@ func _bubble_score_unfair_trap(pos: Vector2i) -> float:
 func _bubble_blast_cells(center: Vector2i) -> Array:
 	"""The 3x3 (radius 1) sticky cells a bubble at `center` would create,
 	clipped to passable/playable cells."""
+	var b = get_arena_bounds()
 	var cells: Array = []
 	for dx in range(-BUBBLE_EXPLOSION_RADIUS, BUBBLE_EXPLOSION_RADIUS + 1):
 		for dz in range(-BUBBLE_EXPLOSION_RADIUS, BUBBLE_EXPLOSION_RADIUS + 1):
 			var c := center + Vector2i(dx, dz)
 			if _is_boundary(c) or _is_npc_zone(c):
 				continue
+			if c.x <= b.min or c.x >= b.max or c.y <= b.min or c.y >= b.max:
+				continue
 			cells.append(c)
 	return cells
 
+func _bubble_footprint(center: Vector2i) -> Array:
+	return _bubble_blast_cells(center)
+	
 func _any_cleanser_holder_near(pos: Vector2i) -> bool:
 	"""True if a player holding a Cleanser charge is within the camping region."""
 	for player in get_tree().get_nodes_in_group("Players"):

scripts/managers/player_movement_manager.gd

@@ -165,9 +165,8 @@ func simple_move_to(grid_position: Vector2i) -> bool:
 			gm.use_cleanser_cell(pid)
 			print("[Move] Cleanser cleared sticky cell at %s (%d cells left)" % [grid_position, gm.cleanser_cells_left.get(pid, 0)])
 		else:
-			print("[Move] Player stepping into sticky cell at %s — slowed" % grid_position)
-			if player.is_multiplayer_authority() or multiplayer.is_server():
-				gm.apply_sticky_slow(player)
+			print("[Move] Failed: Blocked by Gauntlet Sticky cell at %s" % grid_position)
+			return false
 
 	rotate_towards_target(grid_position)