feat(client): integrate D-019 angle sprites into entity renderer (#540)

Migrate entity rendering from ColorRect placeholders to Sprite2D with
rendered PNGs at -72.5° from horizontal. Key changes:
- Sprite2D.centered=false, scale=0.5 for 64px source → 32px runtime
- self_modulate for D-033 relationship tinting (modulate.a reserved
  for D-015 peripheral dimming)
- 8-octant to 4-cardinal direction mapping for sprite selection
- Feet-anchored ENTITY_OFFSET_Y for correct y-sort with tilted sprites
- Facing indicator repositioned to sprite local center (32,32)

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

client/scripts/rendering/entity_renderer.gd

@@ -2,7 +2,7 @@ class_name EntityRenderer
 extends Node2D
 
 # Entity renderer — manages entity sprites under the Entities node
-# Creates/updates/removes ColorRect children based on entity data
+# Creates/updates/removes Sprite2D children based on entity data
 # Entity format (from Protocol v2): {entity_id, x, y, z, kind: {variant, data}, visibility}
 #
 # Position lerping: entity sprites smoothly slide between tiles instead of snapping.
@@ -11,13 +11,15 @@ extends Node2D
 #
 # D-033 colors: Phase 1 defaults by entity kind. Phase 2 (#361) will derive
 # color from RelationshipState via the knowledge graph.
+# #540: Sprites at D-019 angle (-72.5° from horizontal). Textures are neutral greyscale;
+# self_modulate applies D-033 relationship tinting. modulate.a reserved for D-015 dimming.
 
 const TILE_SIZE: int = Constants.TILE_SIZE
-# D-044: 24x32 entity footprint within 32x32 visual tile (64x64 source scaled to 32px runtime)
+# D-044: 24x32 entity footprint within 32x32 visual tile (64x64 source at 0.5 scale = 32px runtime)
 const ENTITY_WIDTH: int = 24
 const ENTITY_HEIGHT: int = 32
-const ENTITY_OFFSET_X: float = (TILE_SIZE - ENTITY_WIDTH) / 2.0   # center horizontally
-const ENTITY_OFFSET_Y: float = (TILE_SIZE - ENTITY_HEIGHT) / 2.0  # center vertically for placeholder. Migration: switch to bottom-anchor (offset = TILE_SIZE - ENTITY_HEIGHT) when real sprites land for correct y-sort ordering.
+const ENTITY_OFFSET_X: float = 0.0                        # sprite fills tile width at 0.5 scale
+const ENTITY_OFFSET_Y: float = TILE_SIZE - ENTITY_HEIGHT  # feet-anchored for correct y-sort with D-019 tilt
 
 # Lerp speed — framerate-independent exponential smoothing.
 # At 12.0: ~70% there after 0.1s, ~95% after 0.25s.
@@ -27,7 +29,8 @@ const LERP_SPEED: float = 12.0
 var entity_nodes: Dictionary = {}    # entity_id -> Node2D
 var _entity_targets: Dictionary = {} # entity_id -> Vector2 (target pixel position)
 var _entity_relationships: Dictionary = {}  # #521: entity_id -> String (last relationship)
-var _entity_tweens: Dictionary = {}  # #521: entity_id -> {target: Color, elapsed: float}
+var _entity_tweens: Dictionary = {}  # #521: entity_id -> {from: Color, target: Color, elapsed: float}
+var _entity_facing: Dictionary = {}  # #540: entity_id -> String ("north"/"east"/"south"/"west")
 
 # #521: Color transition duration in seconds (D-033: "0.5s fade")
 const COLOR_FADE_DURATION: float = 0.5
@@ -48,7 +51,7 @@ func _process(delta: float) -> void:
 		if not node.position.is_equal_approx(target):
 			node.position = node.position.lerp(target, weight)
 
-	# #521: Advance color transitions (manual lerp, testable without SceneTree)
+	# #521: Advance self_modulate transitions (manual lerp, testable without SceneTree)
 	var finished_ids: Array = []
 	for entity_id in _entity_tweens.keys():
 		if not entity_nodes.has(entity_id):
@@ -57,8 +60,9 @@ func _process(delta: float) -> void:
 		var tween_data: Dictionary = _entity_tweens[entity_id]
 		tween_data.elapsed += delta
 		var t := clampf(tween_data.elapsed / COLOR_FADE_DURATION, 0.0, 1.0)
-		var node_c: ColorRect = entity_nodes[entity_id] as ColorRect
-		node_c.color = tween_data.from.lerp(tween_data.target, t)
+		var node_s: Sprite2D = entity_nodes[entity_id] as Sprite2D
+		if node_s:
+			node_s.self_modulate = tween_data.from.lerp(tween_data.target, t)
 		if t >= 1.0:
 			finished_ids.append(entity_id)
 	for eid in finished_ids:
@@ -92,15 +96,23 @@ func update_entities(entities: Array) -> void:
 	for entity_id in ids_to_remove:
 		_remove_entity_node(entity_id)
 
-# Create a new entity node with D-033 color and optional facing indicator
-func _create_entity_node(entity_id: int, entity_data: Dictionary) -> void:
-	var entity_node = ColorRect.new()
-	entity_node.name = "Entity_" + str(entity_id)
-	entity_node.size = Vector2(ENTITY_WIDTH, ENTITY_HEIGHT)
-	entity_node.pivot_offset = Vector2(ENTITY_WIDTH / 2.0, ENTITY_HEIGHT / 2.0)
 
-	# D-033 color by relationship (#521)
-	entity_node.color = _color_for_kind(entity_data)
+# Create a new entity node with D-033 tint and sprite texture at D-019 angle
+func _create_entity_node(entity_id: int, entity_data: Dictionary) -> void:
+	var entity_node := Sprite2D.new()
+	entity_node.name = "Entity_" + str(entity_id)
+	# centered=false: top-left origin aligns with tile grid.
+	# scale=0.5: maps 64px source texture to 32px runtime (D-043, 2x camera = 64px on screen).
+	entity_node.centered = false
+	entity_node.scale = Vector2(0.5, 0.5)
+
+	# 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)
+
+	# D-033: self_modulate for relationship tinting; modulate.a is reserved for D-015 dimming.
+	entity_node.self_modulate = _color_for_kind(entity_data)
 
 	add_child(entity_node)
 	entity_nodes[entity_id] = entity_node
@@ -121,12 +133,13 @@ func _create_entity_node(entity_id: int, entity_data: Dictionary) -> void:
 
 	_update_entity_node(entity_id, entity_data)
 
-# Update an existing entity node (target position, visibility dimming, facing)
+
+# Update an existing entity node (target position, sprite direction, visibility dimming, facing)
 func _update_entity_node(entity_id: int, entity_data: Dictionary) -> void:
 	if not entity_nodes.has(entity_id):
 		return
 
-	var entity_node = entity_nodes[entity_id]
+	var node = entity_nodes[entity_id]
 
 	# Update target position — the lerp in _process() will smoothly move there.
 	# Server sends tile-center coords (tile 16 → 16.5), floor to get tile index.
@@ -136,38 +149,39 @@ func _update_entity_node(entity_id: int, entity_data: Dictionary) -> void:
 			floorf(entity_data.y) * TILE_SIZE + ENTITY_OFFSET_Y
 		)
 
-	# #521: Detect relationship change → fade D-033 color (0.5s via _process)
+	# #540: Update sprite texture when facing direction changes
+	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)
+
+	# #521: Detect relationship change → fade D-033 self_modulate (0.5s via _process)
 	var new_rel: String = entity_data.get("relationship", "Unknown")
-	var old_rel: String = _entity_relationships.get(entity_id, "Unknown")
-	if new_rel != old_rel:
+	if new_rel != _entity_relationships.get(entity_id, "Unknown"):
 		_entity_relationships[entity_id] = new_rel
-		var new_color := _color_for_kind(entity_data)
 		_entity_tweens[entity_id] = {
-			"from": entity_node.color,
-			"target": new_color,
+			"from": (node as Sprite2D).self_modulate,
+			"target": _color_for_kind(entity_data),
 			"elapsed": 0.0,
 		}
 
-	# Note: modulate.a (peripheral dimming below) and color (D-033 tint above)
-	# are compositionally independent — both can change simultaneously without
-	# interference. If alpha tweening is added later, coordinate with color tween.
-
-	# v2: Peripheral vision dimming (D-015)
-	# null visibility (v1 backward compat) defaults to full alpha
+	# D-015: Peripheral vision dimming via modulate.a.
+	# Independent from self_modulate (D-033 tint) — both can change simultaneously.
 	var visibility: Variant = entity_data.get("visibility")
 	var target_alpha := Constants.PERIPHERAL_ALPHA if visibility == "Peripheral" else 1.0
-	if not is_equal_approx(entity_node.modulate.a, target_alpha):
-		entity_node.modulate.a = target_alpha
+	if not is_equal_approx(node.modulate.a, target_alpha):
+		node.modulate.a = target_alpha
 
 	# D-054: Update facing indicator from client-side mouse angle (not server).
 	# InputMapper.facing_angle is a continuous float — smoother than octant snapping.
 	if entity_id == GameState.player_entity_id:
-		var indicator = entity_node.get_node_or_null("FacingIndicator")
+		var indicator = node.get_node_or_null("FacingIndicator")
 		if indicator != null:
 			# facing_angle: 0=East, -PI/2=North. Indicator: 0=North (up).
 			# Rotate from North basis: add PI/2 to convert.
 			indicator.rotation = InputMapper.facing_angle + PI / 2.0
 
+
 # Remove an entity node
 func _remove_entity_node(entity_id: int) -> void:
 	if not entity_nodes.has(entity_id):
@@ -179,13 +193,47 @@ func _remove_entity_node(entity_id: int) -> void:
 	_entity_targets.erase(entity_id)
 	_entity_relationships.erase(entity_id)
 	_entity_tweens.erase(entity_id)
+	_entity_facing.erase(entity_id)
+
 
 # D-033 color by entity kind — delegates to Constants.color_for_entity_kind
 static func _color_for_kind(entity_data: Dictionary) -> Color:
 	return Constants.color_for_entity_kind(entity_data)
 
-# Add a facing direction indicator triangle to the player entity
-func _add_facing_indicator(parent_node: Control) -> void:
+
+# #540: Map entity to current 4-direction sprite key.
+# Player uses GameState.player_facing (8-octant → 4-cardinal). NPCs default "south".
+func _entity_direction(entity_id: int, _entity_data: Dictionary) -> String:
+	if entity_id == GameState.player_entity_id:
+		return _octant_to_direction(GameState.player_facing)
+	# NPCs: no facing field in v1 entity format; south is viewer-facing (D-019 angle)
+	return "south"
+
+
+# Map 8-direction octant string to nearest 4-direction sprite key.
+# N/NW → north, NE/E → east, SE/S → south, SW/W → west
+static func _octant_to_direction(octant: String) -> String:
+	match octant:
+		"North", "Northwest": return "north"
+		"Northeast", "East": return "east"
+		"Southeast", "South": return "south"
+		"Southwest", "West": return "west"
+		_: return "south"
+
+
+# Load the sprite texture for the given 4-direction key.
+# Falls back to null with a push_warning if the asset is missing.
+static func _load_sprite_texture(direction: String) -> Texture2D:
+	var path := "res://assets/sprites/npc_generic_%s_64.png" % direction
+	if ResourceLoader.exists(path):
+		return load(path) as Texture2D
+	push_warning("EntityRenderer: sprite not found: %s" % path)
+	return null
+
+
+# Add a facing direction indicator triangle to the player entity.
+# Indicator position is in Sprite2D local space (64px texture before 0.5 scale → center at (32,32)).
+func _add_facing_indicator(parent_node: Node2D) -> void:
 	var indicator := Polygon2D.new()
 	indicator.name = "FacingIndicator"
 	var s := Constants.FACING_INDICATOR_SIZE
@@ -197,6 +245,7 @@ func _add_facing_indicator(parent_node: Control) -> void:
 		Vector2(s * 0.6, -offset + s * 0.4),
 	])
 	indicator.color = Constants.ENTITY_COLOR_PLAYER
-	# Position at center of parent ColorRect — rotation around this point
-	indicator.position = Vector2(ENTITY_WIDTH / 2.0, ENTITY_HEIGHT / 2.0)
+	# Sprite2D local space: 64px texture at scale 0.5 → center of visible sprite at (32,32).
+	# Indicator rotates around this point to track player facing direction.
+	indicator.position = Vector2(32.0, 32.0)
 	parent_node.add_child(indicator)

client/tests/test_color_shift.gd

@@ -135,43 +135,43 @@ func test_npc_uses_relationship_color_unknown() -> void:
 	var renderer: Node2D = _make_entity_renderer()
 	var entities: Array = [_make_entity(2, "Npc", "Unknown")]
 	renderer.update_entities(entities)
-	var node: ColorRect = renderer.entity_nodes[2] as ColorRect
+	var node: Sprite2D = renderer.entity_nodes[2] as Sprite2D
 	# Unknown -> teal (both Phase 1 and Phase 2 produce the same result)
-	assert_that(node.color).is_equal(Constants.ENTITY_COLOR_UNKNOWN)
+	assert_that(node.self_modulate).is_equal(Constants.ENTITY_COLOR_UNKNOWN)
 	renderer.queue_free()
 
 func test_npc_uses_relationship_color_friendly() -> void:
 	var renderer: Node2D = _make_entity_renderer()
 	var entities: Array = [_make_entity(2, "Npc", "Friendly")]
 	renderer.update_entities(entities)
-	var node: ColorRect = renderer.entity_nodes[2] as ColorRect
+	var node: Sprite2D = renderer.entity_nodes[2] as Sprite2D
 	if not _entity_uses_relationship(renderer):
 		push_warning("TestColorShift: entity renderer not yet using relationship for color — awaiting #521")
 		renderer.queue_free()
 		return
-	assert_that(node.color).is_equal(Constants.ENTITY_COLOR_FRIENDLY)
+	assert_that(node.self_modulate).is_equal(Constants.ENTITY_COLOR_FRIENDLY)
 	renderer.queue_free()
 
 func test_npc_uses_relationship_color_poi() -> void:
 	var renderer: Node2D = _make_entity_renderer()
 	var entities: Array = [_make_entity(2, "Npc", "PersonOfInterest")]
 	renderer.update_entities(entities)
-	var node: ColorRect = renderer.entity_nodes[2] as ColorRect
+	var node: Sprite2D = renderer.entity_nodes[2] as Sprite2D
 	if not _entity_uses_relationship(renderer):
 		renderer.queue_free()
 		return
-	assert_that(node.color).is_equal(Constants.ENTITY_COLOR_POI)
+	assert_that(node.self_modulate).is_equal(Constants.ENTITY_COLOR_POI)
 	renderer.queue_free()
 
 func test_npc_uses_relationship_color_hostile() -> void:
 	var renderer: Node2D = _make_entity_renderer()
 	var entities: Array = [_make_entity(2, "Npc", "Hostile")]
 	renderer.update_entities(entities)
-	var node: ColorRect = renderer.entity_nodes[2] as ColorRect
+	var node: Sprite2D = renderer.entity_nodes[2] as Sprite2D
 	if not _entity_uses_relationship(renderer):
 		renderer.queue_free()
 		return
-	assert_that(node.color).is_equal(Constants.ENTITY_COLOR_HOSTILE)
+	assert_that(node.self_modulate).is_equal(Constants.ENTITY_COLOR_HOSTILE)
 	renderer.queue_free()
 
 func test_player_color_ignores_relationship() -> void:
@@ -179,8 +179,8 @@ func test_player_color_ignores_relationship() -> void:
 	var renderer: Node2D = _make_entity_renderer()
 	var entities: Array = [_make_entity(1, "Player", "Hostile")]
 	renderer.update_entities(entities)
-	var node: ColorRect = renderer.entity_nodes[1] as ColorRect
-	assert_that(node.color).is_equal(Constants.ENTITY_COLOR_PLAYER)
+	var node: Sprite2D = renderer.entity_nodes[1] as Sprite2D
+	assert_that(node.self_modulate).is_equal(Constants.ENTITY_COLOR_PLAYER)
 	renderer.queue_free()
 
 func test_object_color_ignores_relationship() -> void:
@@ -188,8 +188,8 @@ func test_object_color_ignores_relationship() -> void:
 	var renderer: Node2D = _make_entity_renderer()
 	var entities: Array = [_make_entity(3, "Object", "Friendly")]
 	renderer.update_entities(entities)
-	var node: ColorRect = renderer.entity_nodes[3] as ColorRect
-	assert_that(node.color).is_equal(Constants.ENTITY_COLOR_OBJECT)
+	var node: Sprite2D = renderer.entity_nodes[3] as Sprite2D
+	assert_that(node.self_modulate).is_equal(Constants.ENTITY_COLOR_OBJECT)
 	renderer.queue_free()
 
 
@@ -204,20 +204,20 @@ func test_color_shift_not_instant() -> void:
 	var renderer: Node2D = _make_entity_renderer()
 	var entities_before: Array = [_make_entity(2, "Npc", "Friendly")]
 	renderer.update_entities(entities_before)
-	var node: ColorRect = renderer.entity_nodes[2] as ColorRect
+	var node: Sprite2D = renderer.entity_nodes[2] as Sprite2D
 	if not _entity_uses_relationship(renderer):
 		renderer.queue_free()
 		return
 	# Change relationship to Hostile
 	var entities_after: Array = [_make_entity(2, "Npc", "Hostile")]
 	renderer.update_entities(entities_after)
-	# Immediately after update, color should NOT yet be the target
-	var color_after_immediate: Color = node.color
+	# Immediately after update, self_modulate should NOT yet be the target
+	var color_after_immediate: Color = node.self_modulate
 	if not _renderer_has_tween_support(renderer):
 		push_warning("TestColorShift: tween on relationship change not implemented yet — awaiting #521")
 		renderer.queue_free()
 		return
-	# The color should NOT be exactly the target yet (tween in progress)
+	# The self_modulate should NOT be exactly the target yet (tween in progress)
 	assert_that(color_after_immediate != Constants.ENTITY_COLOR_HOSTILE).is_true()
 	renderer.queue_free()
 
@@ -236,8 +236,8 @@ func test_color_shift_reaches_target() -> void:
 	while elapsed < 1.5:
 		renderer._process(1.0 / 60.0)
 		elapsed += 1.0 / 60.0
-	var node: ColorRect = renderer.entity_nodes[2] as ColorRect
-	assert_that(node.color.is_equal_approx(Constants.ENTITY_COLOR_HOSTILE)).is_true()
+	var node: Sprite2D = renderer.entity_nodes[2] as Sprite2D
+	assert_that(node.self_modulate.is_equal_approx(Constants.ENTITY_COLOR_HOSTILE)).is_true()
 	renderer.queue_free()
 
 func test_color_shift_mid_transition_retrigger() -> void:
@@ -263,8 +263,8 @@ func test_color_shift_mid_transition_retrigger() -> void:
 	while elapsed < 1.0:
 		renderer._process(1.0 / 60.0)
 		elapsed += 1.0 / 60.0
-	var node: ColorRect = renderer.entity_nodes[2] as ColorRect
-	assert_that(node.color.is_equal_approx(Constants.ENTITY_COLOR_HOSTILE)).is_true()
+	var node: Sprite2D = renderer.entity_nodes[2] as Sprite2D
+	assert_that(node.self_modulate.is_equal_approx(Constants.ENTITY_COLOR_HOSTILE)).is_true()
 	renderer.queue_free()
 
 
@@ -275,10 +275,10 @@ func test_color_shift_same_relationship_no_tween() -> void:
 		return
 	var entities: Array = [_make_entity(2, "Npc", "Unknown")]
 	renderer.update_entities(entities)
-	var node: ColorRect = renderer.entity_nodes[2] as ColorRect
-	var color_first: Color = node.color
+	var node: Sprite2D = renderer.entity_nodes[2] as Sprite2D
+	var color_first: Color = node.self_modulate
 	renderer.update_entities(entities)
-	var color_second: Color = node.color
+	var color_second: Color = node.self_modulate
 	assert_that(color_first).is_equal(color_second)
 	renderer.queue_free()
 
@@ -354,10 +354,12 @@ func _entity_uses_relationship(renderer: Node2D) -> bool:
 	renderer.update_entities([friendly, hostile])
 	if not renderer.entity_nodes.has(10) or not renderer.entity_nodes.has(11):
 		return false
-	var f_node: ColorRect = renderer.entity_nodes[10] as ColorRect
-	var h_node: ColorRect = renderer.entity_nodes[11] as ColorRect
-	var f_color: Color = f_node.color
-	var h_color: Color = h_node.color
+	var f_node: Sprite2D = renderer.entity_nodes[10] as Sprite2D
+	var h_node: Sprite2D = renderer.entity_nodes[11] as Sprite2D
+	if not f_node or not h_node:
+		return false
+	var f_color: Color = f_node.self_modulate
+	var h_color: Color = h_node.self_modulate
 	var uses_rel: bool = not f_color.is_equal_approx(h_color)
 	renderer.update_entities([])
 	return uses_rel

client/tests/test_sprite_integration.gd

@@ -0,0 +1,195 @@
+## Sprint 16 #540: Sprite integration tests.
+## Tests z-sorting with real sprites, 24x32 D-044 footprint within D-066 64x64
+## bounding box, sprite asset existence from #541, and fog shader independence.
+## Spec refs: D-019, D-043, D-044, D-049, D-066, #540, #541.
+class_name TestSpriteIntegration
+extends GdUnitTestSuite
+
+var EntityRendererScript = load("res://scripts/rendering/entity_renderer.gd")
+
+
+func before_test() -> void:
+	GameState.player_entity_id = 1
+	GameState.player_position = Vector2.ZERO
+	GameState.visible_entities = []
+
+
+# -- Helpers -------------------------------------------------------------------
+
+func _make_entity_renderer() -> Node2D:
+	var renderer = Node2D.new()
+	renderer.set_script(EntityRendererScript)
+	add_child(renderer)
+	return renderer
+
+
+# -- Footprint constants: D-044 spec (S16-S01, S16-S02) -----------------------
+
+func test_entity_footprint_matches_d044_spec() -> void:
+	# S16-S01: D-044 specifies 24x32 entity footprint within 32x32 visual tile.
+	# (64x64 source sprite scaled to 32px runtime at 2x retina per D-066).
+	assert_that(EntityRenderer.ENTITY_WIDTH).override_failure_message(
+		"D-044: ENTITY_WIDTH must be 24px"
+	).is_equal(24)
+	assert_that(EntityRenderer.ENTITY_HEIGHT).override_failure_message(
+		"D-044: ENTITY_HEIGHT must be 32px"
+	).is_equal(32)
+
+
+func test_entity_footprint_within_d066_2x2_sim_tile_bounding_box() -> void:
+	# S16-S02: D-066 requires entity sprite footprint contained within 2x2 sim tile
+	# bounding box. At 32px/tile → 64x64px max. Entity must fit to keep interaction
+	# range (2 sim tiles) accurate with the tilted perspective.
+	var tile_2x: int = Constants.TILE_SIZE * 2
+	assert_that(EntityRenderer.ENTITY_WIDTH <= tile_2x).override_failure_message(
+		"D-066: ENTITY_WIDTH %d must fit within 2x tile width %dpx" % [
+			EntityRenderer.ENTITY_WIDTH, tile_2x]
+	).is_true()
+	assert_that(EntityRenderer.ENTITY_HEIGHT <= tile_2x).override_failure_message(
+		"D-066: ENTITY_HEIGHT %d must fit within 2x tile height %dpx" % [
+			EntityRenderer.ENTITY_HEIGHT, tile_2x]
+	).is_true()
+
+
+func test_entity_width_fits_within_single_tile() -> void:
+	# S16-S03: Entity width (24) < TILE_SIZE (32) → centered within tile.
+	# Ensures horizontal centering offset is positive and entity doesn't overflow.
+	assert_that(EntityRenderer.ENTITY_WIDTH < Constants.TILE_SIZE).override_failure_message(
+		"Entity width must be less than TILE_SIZE for centered layout"
+	).is_true()
+	assert_that(EntityRenderer.ENTITY_OFFSET_X >= 0.0).override_failure_message(
+		"ENTITY_OFFSET_X must be non-negative for horizontal centering"
+	).is_true()
+
+
+# -- Pixel position (S16-S04) -------------------------------------------------
+
+func test_entity_pixel_position_at_tile_3_7() -> void:
+	# S16-S04: Entity at tile (3.0, 7.0) → pixel position must be
+	# (3 * TILE_SIZE + ENTITY_OFFSET_X, 7 * TILE_SIZE + ENTITY_OFFSET_Y).
+	var renderer := _make_entity_renderer()
+	var entity := [{"entity_id": 10, "x": 3.0, "y": 7.0, "z": 0,
+		"kind": {"variant": "Npc", "data": null}}]
+	renderer.update_entities(entity)
+	var node = renderer.entity_nodes[10]
+	var expected_x := 3.0 * Constants.TILE_SIZE + EntityRenderer.ENTITY_OFFSET_X
+	var expected_y := 7.0 * Constants.TILE_SIZE + EntityRenderer.ENTITY_OFFSET_Y
+	assert_that(node.position.x).override_failure_message(
+		"Entity x must be tile_x * TILE_SIZE + ENTITY_OFFSET_X"
+	).is_equal_approx(expected_x, 0.1)
+	assert_that(node.position.y).override_failure_message(
+		"Entity y must be tile_y * TILE_SIZE + ENTITY_OFFSET_Y"
+	).is_equal_approx(expected_y, 0.1)
+	renderer.queue_free()
+
+
+# -- Z-sort ordering: D-049 y-based (S16-S05, S16-S06) -----------------------
+
+func test_z_sort_south_entity_has_higher_pixel_y() -> void:
+	# S16-S05: D-049 y-sort — entity at y=8 (south) must have higher pixel.y
+	# than entity at y=4 (north). Godot y-sort renders higher-y on top.
+	# With tilted sprites, south-facing entity must visually overlap northern.
+	var renderer := _make_entity_renderer()
+	var entities := [
+		{"entity_id": 20, "x": 5.0, "y": 4.0, "z": 0, "kind": {"variant": "Npc", "data": null}},
+		{"entity_id": 21, "x": 5.0, "y": 8.0, "z": 0, "kind": {"variant": "Npc", "data": null}},
+	]
+	renderer.update_entities(entities)
+	var north_node = renderer.entity_nodes[20]
+	var south_node = renderer.entity_nodes[21]
+	assert_that(south_node.position.y > north_node.position.y).override_failure_message(
+		"Entity at y=8 must have higher pixel.y than entity at y=4 for y-sort"
+	).is_true()
+	renderer.queue_free()
+
+
+func test_z_sort_y_position_difference_equals_tile_size() -> void:
+	# S16-S06: Two entities one tile apart in y → pixel y difference = TILE_SIZE.
+	# Verifies position calculation is consistent for adjacent tiles.
+	var renderer := _make_entity_renderer()
+	var entities := [
+		{"entity_id": 30, "x": 5.0, "y": 3.0, "z": 0, "kind": {"variant": "Npc", "data": null}},
+		{"entity_id": 31, "x": 5.0, "y": 4.0, "z": 0, "kind": {"variant": "Npc", "data": null}},
+	]
+	renderer.update_entities(entities)
+	var node3 = renderer.entity_nodes[30]
+	var node4 = renderer.entity_nodes[31]
+	var delta_y := node4.position.y - node3.position.y
+	assert_that(delta_y).override_failure_message(
+		"Adjacent tiles must differ by exactly TILE_SIZE (%dpx) in y" % Constants.TILE_SIZE
+	).is_equal_approx(float(Constants.TILE_SIZE), 0.1)
+	renderer.queue_free()
+
+
+func test_z_sort_same_y_different_x_no_y_difference() -> void:
+	# S16-S07: Two entities at same y but different x → same pixel.y.
+	# Horizontal position must not affect y-sort order.
+	var renderer := _make_entity_renderer()
+	var entities := [
+		{"entity_id": 40, "x": 2.0, "y": 5.0, "z": 0, "kind": {"variant": "Npc", "data": null}},
+		{"entity_id": 41, "x": 8.0, "y": 5.0, "z": 0, "kind": {"variant": "Npc", "data": null}},
+	]
+	renderer.update_entities(entities)
+	var left_node = renderer.entity_nodes[40]
+	var right_node = renderer.entity_nodes[41]
+	assert_that(left_node.position.y).override_failure_message(
+		"Entities at same y-tile must have same pixel.y regardless of x"
+	).is_equal_approx(right_node.position.y, 0.1)
+	renderer.queue_free()
+
+
+# -- Sprite assets from #541 (S16-S08, S16-S09) --------------------------------
+
+func test_npc_sprite_assets_exist_for_all_cardinal_directions() -> void:
+	# S16-S08: #541 delivers 64px NPC sprites for all four cardinal directions.
+	# entity_renderer.gd must be able to load these paths.
+	for direction in ["north", "east", "south", "west"]:
+		var path := "res://assets/sprites/npc_generic_%s_64.png" % direction
+		assert_that(ResourceLoader.exists(path)).override_failure_message(
+			"NPC sprite missing: %s" % path
+		).is_true()
+
+
+func test_wall_sprite_assets_exist_for_all_cardinal_directions() -> void:
+	# S16-S09: #541 delivers 64px wall sprites for all four cardinal directions.
+	for direction in ["north", "east", "south", "west"]:
+		var path := "res://assets/sprites/wall_structural_%s_64.png" % direction
+		assert_that(ResourceLoader.exists(path)).override_failure_message(
+			"Wall sprite missing: %s" % path
+		).is_true()
+
+
+# -- Fog shader independence: D-019 (S16-S10, S16-S11) -----------------------
+
+func test_fog_shader_script_and_gdshader_load_correctly() -> void:
+	# S16-S10: fog_shader.gd and fog.gdshader must remain intact after sprite
+	# changes. D-019: "fog vision cone math remains pure 2D" — unaffected by
+	# the art-direction tilt baked into sprites.
+	assert_that(ResourceLoader.exists("res://scripts/rendering/fog_shader.gd")).override_failure_message(
+		"fog_shader.gd must load correctly — must not be affected by sprite changes"
+	).is_true()
+	assert_that(ResourceLoader.exists("res://shaders/fog.gdshader")).override_failure_message(
+		"fog.gdshader must exist — fog is screen-space and sprite-independent"
+	).is_true()
+
+
+func test_fog_update_runs_independently_of_entity_renderer_state() -> void:
+	# S16-S11: FogState.update_from_state() must succeed with no entity renderer
+	# active. D-019: fog driven by LOS mask (visible_positions), not sprites.
+	var fog = get_node_or_null("/root/FogState")
+	if fog == null:
+		push_warning("TestSpriteIntegration: FogState not available — fog independence test skipped")
+		return
+	# Provide visibility data but no entity renderer context
+	GameState.visible_positions = {Vector2i(5, 5): true, Vector2i(6, 5): true}
+	GameState.visibility_sectors = {
+		Vector2i(5, 5): "Forward",
+		Vector2i(6, 5): "Peripheral",
+	}
+	if fog.has_method("update_from_state"):
+		fog.update_from_state()
+		assert_that(fog.visibility_texture).override_failure_message(
+			"FogState visibility_texture must be populated independently of sprite state"
+		).is_not_null()
+	GameState.visible_positions.clear()
+	GameState.visibility_sectors.clear()