diff --git a/MEMORY.md b/MEMORY.md
index 2eedc78..5a5beb1 100644
--- a/MEMORY.md
+++ b/MEMORY.md
@@ -4,6 +4,14 @@ Session memory for durable decisions, state, and gotchas. Keep concise, remove o
 
 ## Decisions
 
+- **Collider coverage gate (2026-11-03):** `WorldBuilder` sets `library_prop` metadata on every
+  node in `library_nodes`, and `NON_BLOCKING_LIBRARY` (`marquee`, `wall_lantern`, `handrail`,
+  `double_door`) documents the mounted/decorative pieces that intentionally publish no
+  walk-blocking body. `test_world.gd` verifies placed props have `Collision` + `Shape` +
+  `Avoidance` in all three venues, and that library dressing has a body unless exempt. Both
+  were mutation-checked (removing `_add_prop_collision` fails 3 tests; dropping `handrail` from
+  the exemption list fails with the node name). Suite is 275/275. Add the metadata when adding a
+  new library placement, or the coverage test will report it.
 - **3D review gates (2026-11-03):** `tools/test_blender_assets.py` now gates texel density
   (all five character slots present, 40–400 px/m authored, ≥250 px/m effective fabric), and
   `tools/test_model_review.py` gates scorecard coverage (every `CHARACTERS`/`GEAR`/`PROPS` entry
diff --git a/TODO.md b/TODO.md
index 65d058c..a1cdf2b 100644
--- a/TODO.md
+++ b/TODO.md
@@ -122,8 +122,14 @@ except the rebuilt assets themselves.
       and the 40–400 px/m authored band plus the 250 px/m fabric floor; the pose→bone contract is
       covered by `test_pose_reaches_the_skeleton_bones`; LOD/impostor already has
       `test_avatar_mesh_budget_and_lod_swap`. Collider coverage is still open — split below.)
-- [ ] Add a collider/proxy coverage check: every library prop that blocks walking has a
+- [x] Add a collider/proxy check: every library prop that blocks walking has a
       `StaticBody3D` + `NavigationObstacle3D`, checked against the catalogue.
+      (`world_builder.gd` tags every library node with a `library_prop` meta and declares the
+      non-blocking `marquee`/`handrail`/`lantern`/`door` set; two tests in `test_world.gd`
+      verify placed props (body + shape + avoidance radius, all three venues) and library
+      dressing (body unless documented exempt). Mutation-checked: removing `_add_prop_collision`
+      fails 3 tests, dropping `handrail` from the exemption list fails with the exact node.
+      Suite is 275/275.)
 - [x] Add a coverage test so every catalogue asset has a scorecard row and verdict.
       (`tools/test_model_review.py`: every `CHARACTERS`/`GEAR`/`PROPS` entry needs a row in
       `docs/3d-model-review.md`, and character rows need a non-empty verdict.)
diff --git a/src/game/world_builder.gd b/src/game/world_builder.gd
index e5fd316..6f68590 100644
--- a/src/game/world_builder.gd
+++ b/src/game/world_builder.gd
@@ -41,6 +41,11 @@ const LIBRARY_PROPS := ["bollard", "bench", "trash_bin", "planter_box",
 	"newspaper_box", "fire_hydrant", "street_lamp", "street_tree", "traffic_cone",
 	"palm_tree", "round_planter", "a_frame_sign", "crowd_barrier", "stanchion",
 	"security_podium"]
+## Library pieces that are mounted above head height, part of the building shell or
+## purely decorative, so they intentionally publish no walk-blocking body. Anything
+## else in `library_nodes` must carry a `StaticBody3D` + `NavigationObstacle3D`
+## (guarded by `test_library_dressing_collision_matches_the_documented_exemptions`).
+const NON_BLOCKING_LIBRARY := ["marquee", "wall_lantern", "handrail", "double_door"]
 
 var root: Node3D = null
 ## Door lock indicator mesh near the handle; toggled by GameManager.
@@ -336,6 +341,7 @@ func _build_building() -> void:
 		door_model.position = Vector3(0, 0.0, front + 0.16)
 		building.add_child(door_model)
 		library_nodes.append(door_model)
+		door_model.set_meta("library_prop", "double_door")
 		_apply_library_ao(door_model, "double_door")
 		for material in _emissive_materials(door_model):
 			if not _lamp_bulb_mats.has(material):
@@ -1674,6 +1680,7 @@ func _build_marquee() -> void:
 		library.position = Vector3(0, 5.62, -3.9)
 		root.add_child(library)
 		library_nodes.append(library)
+		library.set_meta("library_prop", "marquee")
 		_apply_library_ao(library, "marquee")
 		for material in _emissive_materials(library):
 			if not _marquee_emissive.has(material):
@@ -1714,6 +1721,7 @@ func _build_library_dressing() -> void:
 			rail.rotation_degrees.y = 90.0
 			root.add_child(rail)
 			library_nodes.append(rail)
+			rail.set_meta("library_prop", "handrail")
 			_apply_library_ao(rail, "handrail")
 	if _feature("sedan") and ResourceLoader.exists(BLENDER_PROP_DIR + "sedan.glb"):
 		var sedan_pos: Vector3 = spec.get("sedan_position", Vector3(6.0, 0.1, 17.0))
@@ -1724,6 +1732,7 @@ func _build_library_dressing() -> void:
 			_apply_car_paint(sedan)
 		if not library_nodes.has(sedan):
 			library_nodes.append(sedan)
+		sedan.set_meta("library_prop", "sedan")
 		for material in _emissive_materials(sedan):
 			if not _lamp_bulb_mats.has(material):
 				_lamp_bulb_mats.append(material)
@@ -1795,6 +1804,7 @@ func _add_wall_lantern(pos: Vector3, with_light: bool) -> void:
 	lantern.position = pos
 	root.add_child(lantern)
 	library_nodes.append(lantern)
+	lantern.set_meta("library_prop", "wall_lantern")
 	_apply_library_ao(lantern, "wall_lantern")
 	for material in _emissive_materials(lantern):
 		if not _lamp_bulb_mats.has(material):
@@ -2095,6 +2105,7 @@ func _add_prop_model(parent: Node3D, prop: String, pos: Vector3,
 		if ResourceLoader.exists(BLENDER_PROP_DIR + prop + ".glb"):
 			library_props.append(prop)
 			library_nodes.append(holder)
+			holder.set_meta("library_prop", prop)
 			_apply_library_ao(model, prop)
 	else:
 		var fallback := _fallback_prop(prop)
diff --git a/src/test/tests/test_world.gd b/src/test/tests/test_world.gd
index f01afec..55ff5f0 100644
--- a/src/test/tests/test_world.gd
+++ b/src/test/tests/test_world.gd
@@ -296,3 +296,61 @@ func test_door_indicator_built() -> bool:
 		return a and b and c
 	root.free()
 	return a
+
+## 3D review gate: a placed prop that people can walk into must publish both a
+## static body and a navigation-avoidance footprint. A prop whose bounds are
+## empty (broken GLB/fallback) used to lose its collider silently.
+func test_every_placed_prop_has_a_collider_and_avoidance() -> bool:
+	var problems: Array[String] = []
+	for venue in ["hollywood_building", "joke_shop", "tv_studio"]:
+		var root := Node3D.new()
+		var builder := WorldBuilder.new(root, venue)
+		builder.build()
+		var holders := root.find_children("Prop_*", "Node3D", true, false)
+		if holders.size() < 8:
+			problems.append("%s places only %d props" % [venue, holders.size()])
+		for holder in holders:
+			var body := holder.get_node_or_null("Collision") as StaticBody3D
+			var shape := body.get_node_or_null("Shape") as CollisionShape3D if body != null else null
+			var obstacle := holder.get_node_or_null("Avoidance") as NavigationObstacle3D
+			if body == null or shape == null or shape.shape == null:
+				problems.append("%s/%s has no collision shape" % [venue, holder.name])
+			if obstacle == null or obstacle.radius <= 0.0:
+				problems.append("%s/%s has no avoidance radius" % [venue, holder.name])
+		root.free()
+	return TestUtils.check(problems.is_empty(),
+		"placed props are covered: %s" % ", ".join(problems.slice(0, 6)))
+
+## Library dressing must either publish a walk-blocking body or be on the
+## documented mounted/decorative list. The check also proves the metadata that
+## ties a node to its catalogue asset is present.
+func test_library_dressing_collision_matches_the_documented_exemptions() -> bool:
+	var problems: Array[String] = []
+	for venue in ["hollywood_building", "joke_shop", "tv_studio"]:
+		var root := Node3D.new()
+		var builder := WorldBuilder.new(root, venue)
+		builder.build()
+		if builder.library_nodes.is_empty():
+			problems.append("%s placed no library dressing" % venue)
+		for node in builder.library_nodes:
+			if not is_instance_valid(node):
+				continue
+			var prop := str(node.get_meta("library_prop", ""))
+			if prop == "":
+				problems.append("%s/%s has no library_prop metadata" % [venue, node.name])
+				continue
+			if WorldBuilder.NON_BLOCKING_LIBRARY.has(prop):
+				continue
+			if _walk_blocking_body(node) == null:
+				problems.append("%s/%s (%s) blocks walking without a body" % [venue, node.name, prop])
+		root.free()
+	return TestUtils.check(problems.is_empty(),
+		"library dressing is covered: %s" % ", ".join(problems.slice(0, 6)))
+
+func _walk_blocking_body(node: Node) -> StaticBody3D:
+	for child in node.find_children("*", "StaticBody3D", true, false):
+		var body := child as StaticBody3D
+		for shape in body.find_children("*", "CollisionShape3D", true, false):
+			if (shape as CollisionShape3D).shape != null:
+				return body
+	return null