It was built the other way round on a misreading of two screenshots: the pattern
held {value} and the per-relay boxes held numbers to drop into it. The ask was
simpler and better — {value} is the name typed in Relay labels, so a switch
addressed by antenna name is one pattern instead of eight URLs:
http://10.10.10.100/relay?on={value} relay 1 named Ant1 → ?on=Ant1
Renaming the antenna re-addresses it, and the name on the button and the name on
the wire cannot drift apart because they are the same string. It works in the
per-relay URLs and in the patterns alike, so the per-relay boxes go back to
holding URLs and nothing about them changes meaning any more.
The label is percent-encoded with %20 rather than "+" for a space: "+" is a
space only in a query string and a literal plus in a path, and this can land in
either half of a URL.
{value} on a relay with no label would send "?on=", an empty parameter that most
boards answer with a cheerful 200 and no movement. The driver refuses it and
names the label as what is missing; the editor warns while it is being typed,
beside the empty box rather than after an antenna fails to switch. The labels
also join the driver's cache key — they are part of the wire format now.