How can I restore indentation in this setup?
\documentclass{article}
\usepackage[showframe]{geometry}
\usepackage{marginnote,lipsum}
\reversemarginpar
\setlength{\marginparwidth}{1.1in}
\ProvideDocumentCommand{\LetterSection}{m}{%
\par
\smallskip
\leavevmode
\marginnote{%
\raggedleft
\footnotesize
% \sffamily
% \scshape
\strut #1
}[1pt]%
% \ignorespaces
}
\begin{document}
\LetterSection{test}
\noindent\lipsum[1][1]
\end{document}
In my opinion you're misusing \marginnote.
\documentclass{article}
\usepackage[
letterpaper,% since you're using inches
showframe,
]{geometry}
\usepackage{lipsum}
\NewDocumentCommand{\LetterSection}{m}{%
\par
\smallskip
\noindent
\makebox[0pt][r]{%
\smash{\parbox[t]{1.1in}{\setuplettersection #1}}%
\hspace{\marginparsep}%
}%
\ignorespaces
}
\newcommand{\setuplettersection}{%
\raggedleft
\footnotesize
% \sffamily
% \scshape
}
\begin{document}
\LetterSection{test}
\lipsum[1][1-3]
\LetterSection{Longer text for the margin note}
\lipsum[1][1][1-3]
\end{document}
I see no reason at all for \ProvideDocumentCommand.
You can use \OmitIndent in the para/begin hook to suppress indentation.
I added a * form to suppress the suppression of indentation, in case you need that, too.
\documentclass{article}
\usepackage[showframe,marginparwidth=1.1in]{geometry}
\usepackage{marginnote,lipsum}
\reversemarginpar
\ProvideDocumentCommand{\LetterSection}{sm}{%
\smallskip
\par
\marginnote{%
\raggedleft
\footnotesize
\strut #2
\AddToHookNext {para/begin}{%
\IfBooleanF{#1}{\OmitIndent}%
}%
}[1pt]%
}
\begin{document}
\LetterSection{test}
\lipsum[1][1]
\LetterSection*{test}
\lipsum[1][1]
\end{document}
\leavevmode\noindent text,\noindenthas no effect.\leavevmodeand is not related withmarginnote. Why did you add this\leavevmode?