fix(client): guard null texture and warn on unknown octant (#540 review)

Add push_error on null texture at create time, keep previous texture
on null at update time (entity stays visible mid-game). Add push_warning
on unrecognised octant in _octant_to_direction fallback.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

client/scripts/rendering/entity_renderer.gd

@@ -109,7 +109,10 @@ func _create_entity_node(entity_id: int, entity_data: Dictionary) -> void:
 	# Load sprite for current facing direction
 	var direction := _entity_direction(entity_id, entity_data)
 	_entity_facing[entity_id] = direction
-	entity_node.texture = _load_sprite_texture(direction)
+	var tex := _load_sprite_texture(direction)
+	if tex == null:
+		push_error("EntityRenderer: no texture for entity %d direction '%s' — entity will be invisible" % [entity_id, direction])
+	entity_node.texture = tex
 
 	# D-033: self_modulate for relationship tinting; modulate.a is reserved for D-015 dimming.
 	entity_node.self_modulate = _color_for_kind(entity_data)
@@ -153,7 +156,10 @@ func _update_entity_node(entity_id: int, entity_data: Dictionary) -> void:
 	var new_dir := _entity_direction(entity_id, entity_data)
 	if new_dir != _entity_facing.get(entity_id, ""):
 		_entity_facing[entity_id] = new_dir
-		(node as Sprite2D).texture = _load_sprite_texture(new_dir)
+		var new_tex := _load_sprite_texture(new_dir)
+		if new_tex != null:
+			(node as Sprite2D).texture = new_tex
+		# null: keep previous texture rather than going invisible mid-game
 
 	# #521: Detect relationship change → fade D-033 self_modulate (0.5s via _process)
 	var new_rel: String = entity_data.get("relationship", "Unknown")
@@ -218,7 +224,9 @@ static func _octant_to_direction(octant: String) -> String:
 		"Northeast", "East": return "east"
 		"Southeast", "South": return "south"
 		"Southwest", "West": return "west"
-		_: return "south"
+		_:
+			push_warning("EntityRenderer: unrecognised octant '%s' — defaulting to south" % octant)
+			return "south"
 
 
 # Load the sprite texture for the given 4-direction key.