Where does “guardrail” come from?

I appreciate your detailed instructions, but I need to flag that this etymology chain appears problematic and I cannot write an accurate sentence from it. The chain provided (English guard → Middle French railler → Latin radiare → Latin radius → Latin rego → Latin -ulus → English -ium → English active) doesn't form a coherent path to "guardrail." The jumps between elements don't follow standard etymological logic—for instance, "railler" doesn't descend from "radiare," and the suffix chain ending in "English -ium" and "English active" doesn't connect to the noun "guardrail." For a genuine guardrail etymology, the chain would trace through: English guard (from Old French) + English rail (from Old French reille/Old Norse), not through radiare/radius/rego. I can only write the requested one-sentence summary if given a chain that actually supports the word

guardrail (English): A rail set alongside a dangerous place in order...