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_build.luau

@@ -0,0 +1,55 @@
+-- The require sweep passing only proves the modules LOAD. What runs on Play is
+-- MapBuilder actually building. Execute it for real and capture the error.
+local SS = game:GetService("ServerScriptService")
+local out = {}
+local function say(s) table.insert(out, s) end
+
+local serverScript = SS:FindFirstChild("Server")
+local mb
+for _, d in ipairs(SS:GetDescendants()) do
+	if d:IsA("ModuleScript") and d.Name == "MapBuilder" then mb = d end
+end
+say("MapBuilder module: " .. (mb and mb:GetFullName() or "NOT FOUND"))
+if not mb then return table.concat(out, "\n") end
+
+local ok, mod = pcall(require, mb)
+say("require: " .. (ok and "ok" or ("FAIL " .. tostring(mod))))
+if not ok then return table.concat(out, "\n") end
+
+say("exports: " .. type(mod))
+if type(mod) == "table" then
+	local keys = {}
+	for k, v in pairs(mod) do table.insert(keys, ("%s(%s)"):format(tostring(k), type(v))) end
+	table.sort(keys)
+	say("  " .. table.concat(keys, ", "))
+end
+
+-- Clear any existing map so we build from scratch, exactly like a fresh run.
+local existing = workspace:FindFirstChild("Map")
+say("existing Map in workspace: " .. (existing and "yes" or "no"))
+
+local buildFn = type(mod) == "table" and (mod.Build or mod.build or mod.BuildMap)
+if type(buildFn) ~= "function" then
+	say("NO BUILD FUNCTION EXPORTED -- cannot test build path")
+	return table.concat(out, "\n")
+end
+
+if existing then existing:Destroy() end
+local t0 = os.clock()
+local bok, berr = pcall(buildFn)
+local dt = os.clock() - t0
+say(("build pcall: %s  (%.2fs)"):format(bok and "OK" or "FAIL", dt))
+if not bok then
+	say("BUILD ERROR: " .. tostring(berr):sub(1, 600))
+	return table.concat(out, "\n")
+end
+
+local m = workspace:FindFirstChild("Map")
+say("Map after build: " .. (m and "present" or "MISSING"))
+if m then
+	local n = #m:GetDescendants()
+	say("descendants: " .. n)
+	if n == 0 then say("CONTROL FAIL: map built but empty") end
+end
+
+return table.concat(out, "\n")