docs: add reply_in_thread config to Slack docs

By default, Hermes always threads replies to channel messages. Teams
that prefer direct channel replies had no way to opt out without
patching the source.

Add a reply_in_thread option (default: true) to the Slack platform
extra config:

  platforms:
    slack:
      extra:
        reply_in_thread: false

When false, _resolve_thread_ts() returns None for top-level channel
messages, so replies go directly to the channel. Messages already
inside an existing thread are still replied in-thread to preserve
conversation context. Default is true for full backward compatibility.

gateway/platforms/slack.py

@@ -323,7 +323,18 @@ class SlackAdapter(BasePlatformAdapter):
 
         Prefers metadata thread_id (the thread parent's ts, set by the
         gateway) over reply_to (which may be a child message's ts).
+
+        When ``reply_in_thread`` is ``false`` in the platform extra config,
+        top-level channel messages receive direct channel replies instead of
+        thread replies.  Messages that originate inside an existing thread are
+        always replied to in-thread to preserve conversation context.
         """
+        # When reply_in_thread is disabled (default: True for backward compat),
+        # only thread messages that are already part of an existing thread.
+        if not self.config.extra.get("reply_in_thread", True):
+            existing_thread = (metadata or {}).get("thread_id") or (metadata or {}).get("thread_ts")
+            return existing_thread or None
+
         if metadata:
             if metadata.get("thread_id"):
                 return metadata["thread_id"]

website/docs/user-guide/messaging/slack.md

@@ -217,6 +217,23 @@ In channels, always @mention the bot. Simply typing a message without mentioning
 This is intentional — it prevents the bot from responding to every message in busy channels.
 :::
 
+### Reply Threading
+
+By default, Hermes replies in a **thread** attached to the original message in channels. If your team prefers replies to go **directly to the channel** instead, you can disable threading:
+
+```yaml
+platforms:
+  slack:
+    extra:
+      reply_in_thread: false
+```
+
+When `reply_in_thread` is `false`:
+- **Channel messages** — Hermes replies directly in the channel (no thread created)
+- **Thread messages** — Hermes still replies inside the existing thread to preserve conversation context
+
+The default is `true` (threaded replies), which matches the original behavior.
+
 ---