How can I get exactly one space in .idx? I know how to get two or none, but not just one

Question

Consider the following MWE:

\documentclass{ltxdoc}
\makeatletter
\newcommand*\myindex[3]{%
  \doc@providetarget
  \index{#1:\levelchar#2\actualchar{\ttfamily#3}\doc@handleencap{usage}}%
}
\makeatother
\makeindex
\begin{document}
\DescribeEnv{myenv}\marg{argument}\par
\myindex{environments}{myenv}{myenv}
\end{document}

While \DescribeEnv indexes myenv with just a single space before myenv, \myindex adds two.

Contents of .idx:

\indexentry{myenv={\ttfamily myenv} (env.)|hdclindex{2}{usage}}{1}
\indexentry{environments:>myenv={\ttfamily myenv}|hdclindex{2}{usage}}{1}
\indexentry{environments:>myenv={\ttfamily  myenv}|hdclindex{3}{usage}}{1}

This results in twice as many index entries as there should be.

Thanks to Heiko Oberdiek's answer I can prevent this using

\documentclass{ltxdoc}
\makeatletter
\newcommand*\myindex[3]{% ateb Heiko Oberdiek https://tex.stackexchange.com/a/412521/
  \doc@providetarget
  @bsphack
  \begingroup
  @sanitize
  @wrindex{#1:\levelchar#2\actualchar{\string\ttfamily #3}\doc@handleencap{usage}}%
}
\makeatother
\makeindex
\begin{document}
\DescribeEnv{myenv}\marg{argument}\par
\myindex{environments}{myenv}{myenv}
\end{document}

which gives me

\indexentry{myenv={\ttfamily myenv} (env.)|hdclindex{2}{usage}}{1}
\indexentry{environments:>myenv={\ttfamily myenv}|hdclindex{2}{usage}}{1}
\indexentry{environments:>myenv={\ttfamilymyenv}|hdclindex{3}{usage}}{1}

but now I have no spaces and I cannot figure out how to keep exactly one. In case it matters, I'm actually doing this with expl3 syntax on, though I could avoid that if necessary.