Aux-lane suppression + PA geometry fixes; probe/verify tooling

MapBuilder.luau
  - Suppress the aux lane across samples 525-550 (AUX_SUPPRESS_FROM/TO),
    honoring the user's hand deletion in Studio so a rebuild no longer
    regenerates it.
  - Smoothstep the width ramp over AUX_BLEND=5 samples on each side. A hard
    cut produced a 26-stud lateral fence jog; the blend removes it.
  - DO NOT remove this suppression. Re-enabling it resurrects geometry the
    user deleted by hand.

rokit.toml
  - rojo 7.5.1 -> 7.7.0 to match the auto-updating Studio plugin.
    Server older than plugin fails the handshake with
    "attempt to index number with 'protocolVersion'".

tools/
  - 34 read-only probe/verify/capture scripts used to measure the datamodel
    instead of reasoning from source.

Verified-good baseline at this commit:
  total parts       16788
  PAWestSlip        60 segs, 34.4 deg total bend, worst 1.4, 0 kinks >5
  PAEastSlip        60 segs, 30.7 deg total bend, worst 1.3, 0 kinks >5
  AuxLane parts     30 (samples 525-550 deliberately absent)
  barrier coverage  823 samples, 0 unguarded
  fence jogs >10st  0

tools/probe_barriergap.luau

@@ -0,0 +1,134 @@
+-- Two questions, measured rather than eyeballed:
+--   (1) WHERE exactly is the mainline missing barriers? Walk the deck edge and
+--       report contiguous runs with no Barrier/EdgeRail within reach.
+--       (User deleted ~106 parts by hand, so gaps are wherever they cut.)
+--   (2) HOW does the south on-ramp differ from the north off-ramp? Compare the
+--       two slips feature-by-feature so "make it look like the other" is a
+--       concrete list of deltas, not a guess.
+local out = {}
+local function say(s) table.insert(out, s) end
+
+local map = workspace:FindFirstChild("Map")
+if not map then return "Map MISSING" end
+
+-- Collect barrier-ish parts into a coarse spatial hash for fast lookup.
+local CELL = 60
+local grid = {}
+local function key(x, z) return math.floor(x / CELL) .. ":" .. math.floor(z / CELL) end
+local barrierCount = 0
+for _, d in ipairs(map:GetDescendants()) do
+	if d:IsA("BasePart") and (d.Name == "Barrier" or d.Name == "EdgeRail") then
+		barrierCount += 1
+		local k = key(d.Position.X, d.Position.Z)
+		grid[k] = grid[k] or {}
+		table.insert(grid[k], d)
+	end
+end
+say(("indexed %d Barrier/EdgeRail parts"):format(barrierCount))
+
+local function nearestBarrier(p)
+	local best = math.huge
+	local cx, cz = math.floor(p.X / CELL), math.floor(p.Z / CELL)
+	for dx = -1, 1 do
+		for dz = -1, 1 do
+			local c = grid[(cx + dx) .. ":" .. (cz + dz)]
+			if c then
+				for _, b in ipairs(c) do
+					local d2 = (Vector3.new(b.Position.X, 0, b.Position.Z) - Vector3.new(p.X, 0, p.Z)).Magnitude
+					-- only count barriers at roughly this height
+					if math.abs(b.Position.Y - p.Y) < 14 and d2 < best then best = d2 end
+				end
+			end
+		end
+	end
+	return best
+end
+
+-- Walk the mainline deck parts to build an ordered centreline.
+local deck = {}
+for _, d in ipairs(map:GetDescendants()) do
+	if d:IsA("BasePart") then
+		local k = d.Name:match("^Road_(%d+)$") or d.Name:match("^Deck_(%d+)$")
+			or d.Name:match("^RoadDeck_(%d+)$")
+		if k then table.insert(deck, { i = tonumber(k), p = d.Position, cf = d.CFrame, sz = d.Size }) end
+	end
+end
+table.sort(deck, function(a, b) return a.i < b.i end)
+say(("mainline deck parts found: %d"):format(#deck))
+
+if #deck > 0 then
+	local UP = Vector3.new(0, 1, 0)
+	local runs = {}
+	local cur = nil
+	for j, s in ipairs(deck) do
+		local fwd = s.cf.LookVector
+		local right = fwd:Cross(UP).Unit
+		local half = s.sz.X / 2
+		-- probe just outboard of each edge
+		local gapL = nearestBarrier(s.p - right * (half + 2)) > 12
+		local gapR = nearestBarrier(s.p + right * (half + 2)) > 12
+		local bad = gapL or gapR
+		if bad then
+			local side = (gapL and gapR) and "BOTH" or (gapL and "L" or "R")
+			if cur and cur.side == side and s.i - cur.last <= 2 then
+				cur.last = s.i; cur.n += 1
+			else
+				if cur then table.insert(runs, cur) end
+				cur = { first = s.i, last = s.i, n = 1, side = side, pos = s.p }
+			end
+		else
+			if cur then table.insert(runs, cur); cur = nil end
+		end
+	end
+	if cur then table.insert(runs, cur) end
+
+	table.sort(runs, function(a, b) return a.n > b.n end)
+	say(("UNBARRIERED RUNS: %d total"):format(#runs))
+	for j = 1, math.min(#runs, 14) do
+		local r = runs[j]
+		say(("  samples %d..%d (%d) side=%s at (%.0f,%.0f,%.0f)"):format(
+			r.first, r.last, r.n, r.side, r.pos.X, r.pos.Y, r.pos.Z))
+	end
+end
+
+-- (2) Compare the two slips.
+say("--- SLIP COMPARISON ---")
+for _, s in ipairs({ "PAWestSlip", "PAEastSlip" }) do
+	local segs, walls, lines, other = {}, 0, 0, {}
+	for _, d in ipairs(map:GetDescendants()) do
+		if d:IsA("BasePart") and d.Name:match("^" .. s) then
+			local k = d.Name:match("^" .. s .. "_Deck_(%d+)$")
+			if k then
+				table.insert(segs, { i = tonumber(k), p = d.Position, sz = d.Size, cf = d.CFrame })
+			elseif d.Name:match("_Wall_") then walls += 1
+			elseif d.Name:match("[Ll]ine") then lines += 1
+			else
+				local nm = d.Name:gsub("^" .. s .. "_", ""):gsub("_%d+$", "")
+				other[nm] = (other[nm] or 0) + 1
+			end
+		end
+	end
+	table.sort(segs, function(a, b) return a.i < b.i end)
+	local ol = {}
+	for k, v in pairs(other) do table.insert(ol, k .. "=" .. v) end
+	table.sort(ol)
+	if #segs > 0 then
+		-- heading of first and last segment: which way does it run?
+		local h1 = segs[1].cf.LookVector
+		local hN = segs[#segs].cf.LookVector
+		-- curvature: total heading change
+		local turn = 0
+		for j = 2, #segs do
+			local a = segs[j - 1].cf.LookVector
+			local b = segs[j].cf.LookVector
+			turn += math.deg(math.acos(math.clamp(a:Dot(b), -1, 1)))
+		end
+		say(("%s: segs=%d walls=%d lines=%d  startY=%.1f endY=%.1f"):format(s, #segs, walls, lines, segs[1].p.Y, segs[#segs].p.Y))
+		say(("   heading first=(%.2f,%.2f) last=(%.2f,%.2f) totalTurn=%.1fdeg"):format(h1.X, h1.Z, hN.X, hN.Z, turn))
+		say(("   start=(%.0f,%.0f,%.0f) end=(%.0f,%.0f,%.0f)"):format(
+			segs[1].p.X, segs[1].p.Y, segs[1].p.Z, segs[#segs].p.X, segs[#segs].p.Y, segs[#segs].p.Z))
+		say("   other parts: " .. (#ol > 0 and table.concat(ol, " ") or "none"))
+	end
+end
+
+return table.concat(out, "\n")