Function describe_handler_annotation_at 

pub fn describe_handler_annotation_at(
    source: &str,
    offset: usize,
) -> Option<String>

v0.140 (ADR 0163): hover for a handler-position annotation (@cache). Handler annotations are not symbols and declare no local, so they miss both the describe_symbol and locals paths — this closes the gap. For the cursor anywhere within a handler’s @cache( … ) annotation, render the formatted annotation followed by a prose description of @cache and its fields. None when the cursor is not inside a handler annotation.