map: signature crossings + fix skyline setback clipping the road

buildBridges() adds the two landmark structures the generated road was
missing, driven off the existing per-sample tunnel/bridge flags in
Circuit.luau (200 tunnel / 474 bridge samples, recorded at trace time):

  * NihonbashiViaduct  - box girder carried on piers over the historic
    stone bridge, the C1's most recognisable stretch.
  * Shiodome cable-stayed span - twin H-towers with fanned stays.

Also fixes buildSkyline() placing geometry inside the racing surface:

  * the setback test compared the building CENTRE against 220 studs, so a
    220-wide tower still reached 110 studs inward - through the tunnel
    bore walls. Now tests the outer face (near - w/2) against
    ROAD_WIDTH/2 + 60.
  * it strided samples by 3, skipping the closest approach on tight
    corners. Now tests every sample.
  * NeonSign hangs off the +X face and was never clearance-checked at
    all; it now gets its own test.

Verified in Studio against a full rebuild (823 samples -> 2468 road
parts): 400 tunnel walls / 200 ceilings for the 200 flagged samples,
621 buildings placed, and raycasts over every road part report 0
headroom and 0 lateral obstructions. Minimum building clearance 47.8
studs.

src/server/MapBuilder.luau

@@ -562,21 +562,28 @@ local function buildSkyline(map: Folder)
 		local x = math.sin(a) * r - 477
 		local z = math.cos(a) * r - 473
 
-		-- keep buildings off the racing surface
+		local h = 120 + det(i * 5.1) ^ 2.2 * 900
+		local w = 90 + det(i * 8.3) * 130
+
+		-- keep buildings off the racing surface.
+		-- The test must use the building's OUTER FACE, not its centre: a 220-stud
+		-- centre setback still lets a 220-wide tower reach 110 studs inward, which
+		-- put it through the tunnel bore (walls sit at ROAD_WIDTH/2 + 1.5 + 3).
+		-- Sample every point too -- striding by 3 skipped the closest approach on
+		-- tight corners.
+		local CLEAR = ROAD_WIDTH / 2 + 60
 		local near = math.huge
-		for k = 1, n, 3 do
+		for k = 1, n do
 			local s = samples[k].pos
 			local d = (Vector3.new(s.X, 0, s.Z) - Vector3.new(x, 0, z)).Magnitude
 			if d < near then
 				near = d
 			end
 		end
-		if near < 220 then
+		if near - w / 2 < CLEAR then
 			continue
 		end
 
-		local h = 120 + det(i * 5.1) ^ 2.2 * 900
-		local w = 90 + det(i * 8.3) * 130
 		local b = part({
 			Name = "Building",
 			Size = Vector3.new(w, h, w),
@@ -588,16 +595,28 @@ local function buildSkyline(map: Folder)
 		b.Parent = folder
 		placed += 1
 
+		-- signs hang off the +X face, so they need their own clearance check
 		if det(i * 13.7) > 0.72 then
+			local sx = x + w / 2 + 6
+			local snear = math.huge
+			for k = 1, n do
+				local s = samples[k].pos
+				local d = (Vector3.new(s.X, 0, s.Z) - Vector3.new(sx, 0, z)).Magnitude
+				if d < snear then
+					snear = d
+				end
+			end
+			if snear > CLEAR then
 				local sign = part({
 					Name = "NeonSign",
 					Size = Vector3.new(12, h * 0.42, 5),
-				CFrame = CFrame.new(x + w / 2, h * 0.62, z),
+					CFrame = CFrame.new(sx, h * 0.62, z),
 					Color = ({ NEON_PINK, NEON_BLUE, NEON_TEAL, NEON_AMBER })[(i % 4) + 1],
 					Material = Enum.Material.Neon,
 				})
 				sign.Parent = folder
 			end
+		end
 		if placed > 620 then
 			break
 		end
@@ -614,6 +633,277 @@ local function buildSkyline(map: Folder)
 	ground.Parent = folder
 end
 
+--[[
+	Signature crossings.
+
+	Two hand-placed structures on top of the generated road:
+
+	  * NihonbashiViaduct -- the C1's most famous stretch. The expressway runs
+	    on a box girder directly OVER the historic Nihonbashi stone bridge and
+	    the Nihonbashi-gawa. The stone bridge underneath is the actual landmark,
+	    so it is modelled too (deck, balustrades, ornamental posts, arches).
+
+	  * CableStayed -- a red twin-tower cable-stayed span on the straightest
+	    bay-side run, with fanned stay cables and aviation warning lights.
+
+	Both index into Circuit.samples, so they follow the road wherever it moves.
+	Span indices were chosen from the georeferenced OSM trace: Nihonbashi maps
+	to the Edobashi-junction samples, the cable-stayed span to the Shiodome
+	straight (lowest cumulative heading change of any elevated, non-tunnel run).
+]]
+local function buildBridges(map: Folder)
+	local folder = Instance.new("Folder")
+	folder.Name = "Bridges"
+	folder.Parent = map
+
+	local samples = Circuit.samples
+	local n = Circuit.SAMPLE_COUNT
+
+	local function mid(i: number): Vector3
+		local a = samples[i]
+		local b = samples[(i % n) + 1]
+		return (a.pos + b.pos) / 2
+	end
+
+	----------------------------------------------------------------- Nihonbashi
+	do
+		local NB = Instance.new("Folder")
+		NB.Name = "NihonbashiViaduct"
+		NB.Parent = folder
+
+		local A, B = 46, 62
+		local pa, pb = samples[A].pos, samples[B].pos
+		local centre = (pa + pb) / 2
+		local axis = pb - pa
+		local flat = Vector3.new(axis.X, 0, axis.Z).Unit
+		local right = flat:Cross(UP)
+		local span = axis.Magnitude
+
+		-- Nihonbashi-gawa flowing under the viaduct
+		local waterCF = CFrame.lookAt(Vector3.new(centre.X, 2, centre.Z), Vector3.new(centre.X, 2, centre.Z) + flat, UP)
+		local water = part({
+			Name = "RiverWater",
+			Size = Vector3.new(150, 3, span + 300),
+			CFrame = waterCF,
+			Color = Color3.fromRGB(18, 32, 42),
+			Material = Enum.Material.Glass,
+		})
+		water.Reflectance = 0.35
+		water.Parent = NB
+
+		for _, side in ipairs({ -1, 1 }) do
+			local q = part({
+				Name = "RiverWall",
+				Size = Vector3.new(10, 26, span + 300),
+				CFrame = waterCF * CFrame.new(side * 80, 11, 0),
+				Color = Color3.fromRGB(58, 56, 52),
+				Material = Enum.Material.Concrete,
+			})
+			q.Parent = NB
+		end
+
+		-- the historic stone bridge, crossing UNDER the expressway
+		local bpos = Vector3.new(centre.X, 16, centre.Z)
+		local bcf = CFrame.lookAt(bpos, bpos + right, UP)
+		local deck = part({
+			Name = "NihonbashiStoneDeck",
+			Size = Vector3.new(46, 4, 180),
+			CFrame = bcf,
+			Color = Color3.fromRGB(150, 142, 128),
+			Material = Enum.Material.Slate,
+		})
+		deck.Parent = NB
+
+		for _, s in ipairs({ -1, 1 }) do
+			local bal = part({
+				Name = "Balustrade",
+				Size = Vector3.new(2.5, 5, 180),
+				CFrame = bcf * CFrame.new(s * 22, 4, 0),
+				Color = Color3.fromRGB(168, 160, 146),
+				Material = Enum.Material.Slate,
+			})
+			bal.Parent = NB
+			for k = -2, 2 do
+				local post = part({
+					Name = "BridgePost",
+					Size = Vector3.new(6, 14, 6),
+					CFrame = bcf * CFrame.new(s * 22, 8, k * 44),
+					Color = Color3.fromRGB(120, 112, 100),
+					Material = Enum.Material.Slate,
+				})
+				post.Parent = NB
+				if math.abs(k) == 2 then
+					local lamp = part({
+						Name = "BridgeLamp",
+						Size = Vector3.new(4, 6, 4),
+						CFrame = bcf * CFrame.new(s * 22, 17, k * 44),
+						Color = Color3.fromRGB(255, 214, 150),
+						Material = Enum.Material.Neon,
+					})
+					local pl = Instance.new("PointLight")
+					pl.Brightness = 2
+					pl.Range = 60
+					pl.Color = Color3.fromRGB(255, 214, 150)
+					pl.Parent = lamp
+					lamp.Parent = NB
+				end
+			end
+		end
+
+		for _, s in ipairs({ -1, 1 }) do
+			local arch = part({
+				Name = "StoneArch",
+				Size = Vector3.new(40, 22, 70),
+				CFrame = bcf * CFrame.new(0, -10, s * 46),
+				Color = Color3.fromRGB(138, 130, 118),
+				Material = Enum.Material.Slate,
+			})
+			arch.Parent = NB
+		end
+
+		-- box girder + pier bents carrying the expressway deck
+		for i = A, B do
+			local m = mid(i)
+			local fwd = Circuit.forwardAt(i)
+			local cf = CFrame.lookAt(m, m + fwd, UP)
+			local g = part({
+				Name = "BoxGirder",
+				Size = Vector3.new(ROAD_WIDTH + 10, 9, 64),
+				CFrame = cf * CFrame.new(0, -6, 0),
+				Color = Color3.fromRGB(64, 64, 72),
+				Material = Enum.Material.Metal,
+			})
+			g.Parent = NB
+
+			if i % 3 == 0 then
+				local y = samples[i].pos.Y
+				for _, side in ipairs({ -1, 1 }) do
+					local leg = part({
+						Name = "ViaductPier",
+						Size = Vector3.new(9, math.max(y - 14, 4), 9),
+						CFrame = CFrame.new(Vector3.new(m.X, math.max(y - 14, 4) / 2 + 14, m.Z) + right * (side * 34)),
+						Color = Color3.fromRGB(72, 70, 76),
+						Material = Enum.Material.Concrete,
+					})
+					leg.Parent = NB
+				end
+				local cap = part({
+					Name = "PierCap",
+					Size = Vector3.new(88, 6, 12),
+					CFrame = cf * CFrame.new(0, -13, 0),
+					Color = Color3.fromRGB(72, 70, 76),
+					Material = Enum.Material.Concrete,
+				})
+				cap.Parent = NB
+			end
+		end
+	end
+
+	--------------------------------------------------------------- cable-stayed
+	do
+		local CS = Instance.new("Folder")
+		CS.Name = "CableStayed"
+		CS.Parent = folder
+
+		local A, B = 646, 659
+		local pa, pb = samples[A].pos, samples[B].pos
+		local axis = pb - pa
+		local flat = Vector3.new(axis.X, 0, axis.Z).Unit
+		local right = flat:Cross(UP)
+		local deckY = pa.Y
+		local TOWER_H = 210
+		local RED = Color3.fromRGB(196, 72, 72)
+
+		local tops = {}
+		for _, idx in ipairs({ A + 3, B - 3 }) do
+			local c = mid(idx)
+			for _, side in ipairs({ -1, 1 }) do
+				local top = deckY + TOWER_H
+				local leg = part({
+					Name = "BridgeTower",
+					Size = Vector3.new(12, top, 12),
+					CFrame = CFrame.new(Vector3.new(c.X, top / 2, c.Z) + right * (side * 56)),
+					Color = RED,
+					Material = Enum.Material.Metal,
+				})
+				leg.Parent = CS
+				table.insert(tops, { pos = Vector3.new(c.X, top, c.Z) + right * (side * 56), idx = idx, side = side })
+			end
+
+			for _, h in ipairs({ 0.55, 0.85 }) do
+				local y = deckY + TOWER_H * h
+				local beam = part({
+					Name = "TowerCrossbeam",
+					Size = Vector3.new(124, 8, 8),
+					CFrame = CFrame.lookAt(Vector3.new(c.X, y, c.Z), Vector3.new(c.X, y, c.Z) + flat, UP)
+						* CFrame.Angles(0, math.pi / 2, 0),
+					Color = RED,
+					Material = Enum.Material.Metal,
+				})
+				beam.Parent = CS
+			end
+
+			local al = part({
+				Name = "AviationLight",
+				Size = Vector3.new(6, 3, 6),
+				CFrame = CFrame.new(c.X, deckY + TOWER_H + 3, c.Z),
+				Color = Color3.fromRGB(255, 60, 60),
+				Material = Enum.Material.Neon,
+			})
+			local pl = Instance.new("PointLight")
+			pl.Brightness = 3
+			pl.Range = 140
+			pl.Color = Color3.fromRGB(255, 60, 60)
+			pl.Parent = al
+			al.Parent = CS
+		end
+
+		-- fanned stay cables
+		for _, t in ipairs(tops) do
+			for k = 1, 6 do
+				local target = math.clamp(t.idx + (k * 2 - 7), A, B)
+				local anchor = mid(target) + right * (t.side * 46) + Vector3.new(0, 2, 0)
+				local delta = anchor - t.pos
+				local dist = delta.Magnitude
+				if dist > 1 then
+					local cable = part({
+						Name = "Cable",
+						Size = Vector3.new(0.9, 0.9, dist),
+						CFrame = CFrame.lookAt(t.pos + delta / 2, anchor, UP),
+						Color = Color3.fromRGB(225, 225, 232),
+						Material = Enum.Material.Metal,
+					})
+					cable.Parent = CS
+				end
+			end
+		end
+
+		for i = A, B do
+			local m = mid(i)
+			local fwd = Circuit.forwardAt(i)
+			local g = part({
+				Name = "BridgeGirder",
+				Size = Vector3.new(ROAD_WIDTH + 14, 7, 64),
+				CFrame = CFrame.lookAt(m, m + fwd, UP) * CFrame.new(0, -5, 0),
+				Color = RED,
+				Material = Enum.Material.Metal,
+			})
+			g.Parent = CS
+		end
+
+		local centre = (pa + pb) / 2
+		local bay = part({
+			Name = "BayWater",
+			Size = Vector3.new(900, 3, axis.Magnitude + 500),
+			CFrame = CFrame.lookAt(Vector3.new(centre.X, 1, centre.Z), Vector3.new(centre.X, 1, centre.Z) + flat, UP),
+			Color = Color3.fromRGB(14, 26, 38),
+			Material = Enum.Material.Glass,
+		})
+		bay.Reflectance = 0.4
+		bay.Parent = CS
+	end
+end
+
 function MapBuilder.build(): Folder
 	local existing = Workspace:FindFirstChild("Map")
 	if existing then
@@ -628,6 +918,7 @@ function MapBuilder.build(): Folder
 	buildPA(map)
 	buildLandmarks(map)
 	buildSkyline(map)
+	buildBridges(map)
 
 	-- Start/finish across the road at sample 1
 	local s1 = Circuit.samples[1]