Clarify EasyCom boundary prelabel taxonomy

manuscript/main/main.tex

@@ -609,6 +609,9 @@ admit nor reject a candidate and do not establish takeover. The LLM and human
 annotator answer whether the wearer stopped because a non-wearer genuinely took
 over the floor. Natural completion, post-completion activity, and within-turn
 pauses are therefore resolved semantically rather than pre-filtered.
+When a wearer activity run is itself only a backchannel within a non-wearer's
+retained turn, its onset supplies the false-entry opportunity; its trailing
+offset is excluded rather than counted again as a false-yield opportunity.
 
 \subsection{False-positive opportunity mining}