The Weixin adapter only recognized errcode=-14 as a session-expired
signal. However, iLink also returns ret=-2 with errmsg="unknown error"
for the same underlying condition (stale session). The adapter treated
ret=-2 as a rate-limit, exhausting retries with the same stale
context_token instead of refreshing the session.
Added _is_stale_session_ret() helper that distinguishes ret=-2 with
"unknown error" from genuine rate limits. Updated both the poll loop
and _send_text_chunk to use the helper.
FixesNousResearch/hermes-agent#17228
e9b96fd050