Once a thread has an active session, a later reply that explicitly
@mentions the bot did not re-fetch Slack thread context, so the agent
missed messages added to the thread after the initial hydrate (e.g.
other bots/integrations replying in multi-agent workflows). The
explicit mention is a fresh intent signal and now triggers a refresh.
Mechanics:
- SessionEntry gains a small persisted metadata dict, with
SessionStore.get/set_session_metadata accessors (survives gateway
restarts via the routing index).
- The adapter stores a per-thread consumption watermark
(slack_thread_watermark:<channel>:<thread>) recording the last
thread ts the session consumed.
- On explicit mention in an active thread, _fetch_thread_context runs
with force_refresh=True (bypassing the TTL cache) and after_ts=<the
watermark>, so only NOT-yet-seen messages are injected — as part of
the new turn via channel_context. Prior conversation history is
never rewritten, preserving prompt caching.
- _fetch_thread_context caches raw conversations.replies payloads so
watermark-scoped re-formatting needs no extra API call; formatting
is split into _format_thread_context.
- Thread session keys are built once in _build_thread_session_key
(shared by the wake gate and the watermark accessors), still via
build_session_key().
Fixes#23918. Supersedes #62299 (keyword-triggered refresh limited to
'investigate' prompts — the mention signal is the general fix).
Salvaged from #23927 by @heathley, rebased onto the plugin adapter
layout and rerouted through channel_context instead of text-prepend.
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