The existing replyStyle section explains the Posts-vs-Threads tradeoff but
doesn't document how the value is actually resolved at send-time, nor what
happens to thread-root context across configurations. Operators who hit
unexpected top-level posts (e.g., requireMention=false setups, long-running
agents whose proactive sends fall outside the live Bot Framework turn) have
no docs-side anchor for understanding which knob to flip.
Add two subsections under Reply Style:
1. Resolution precedence — channel > team > global > implicit default,
plus the requireMention-derived implicit default.
2. Thread context preservation — describes that replyStyle=thread re-attaches
the original thread root on outbound (live and proactive paths after
#78387), with the threadId/activityId fallback for legacy stored refs.
Calls out the deliberate "no thread suffix" behavior for replyStyle=top-level.
Pure documentation change, no behavior or surface impact.
79d9b95e67
