diff --git a/nanobot/bus/events.py b/nanobot/bus/events.py
index a149e20..a48660d 100644
--- a/nanobot/bus/events.py
+++ b/nanobot/bus/events.py
@@ -16,11 +16,12 @@ class InboundMessage:
     timestamp: datetime = field(default_factory=datetime.now)
     media: list[str] = field(default_factory=list)  # Media URLs
     metadata: dict[str, Any] = field(default_factory=dict)  # Channel-specific data
+    session_key_override: str | None = None  # Optional override for thread-scoped sessions
     
     @property
     def session_key(self) -> str:
         """Unique key for session identification."""
-        return f"{self.channel}:{self.chat_id}"
+        return self.session_key_override or f"{self.channel}:{self.chat_id}"
 
 
 @dataclass
diff --git a/nanobot/channels/base.py b/nanobot/channels/base.py
index 3a5a785..3010373 100644
--- a/nanobot/channels/base.py
+++ b/nanobot/channels/base.py
@@ -89,7 +89,8 @@ class BaseChannel(ABC):
         chat_id: str,
         content: str,
         media: list[str] | None = None,
-        metadata: dict[str, Any] | None = None
+        metadata: dict[str, Any] | None = None,
+        session_key: str | None = None,
     ) -> None:
         """
         Handle an incoming message from the chat platform.
@@ -102,6 +103,7 @@ class BaseChannel(ABC):
             content: Message text content.
             media: Optional list of media URLs.
             metadata: Optional channel-specific metadata.
+            session_key: Optional session key override (e.g. thread-scoped sessions).
         """
         if not self.is_allowed(sender_id):
             logger.warning(
@@ -117,7 +119,8 @@ class BaseChannel(ABC):
             chat_id=str(chat_id),
             content=content,
             media=media or [],
-            metadata=metadata or {}
+            metadata=metadata or {},
+            session_key_override=session_key,
         )
         
         await self.bus.publish_inbound(msg)
diff --git a/nanobot/channels/slack.py b/nanobot/channels/slack.py
index b0f9bbb..906593b 100644
--- a/nanobot/channels/slack.py
+++ b/nanobot/channels/slack.py
@@ -179,6 +179,9 @@ class SlackChannel(BaseChannel):
         except Exception as e:
             logger.debug("Slack reactions_add failed: {}", e)
 
+        # Thread-scoped session key for channel/group messages
+        session_key = f"slack:{chat_id}:{thread_ts}" if thread_ts and channel_type != "im" else None
+
         try:
             await self._handle_message(
                 sender_id=sender_id,
@@ -189,8 +192,9 @@ class SlackChannel(BaseChannel):
                         "event": event,
                         "thread_ts": thread_ts,
                         "channel_type": channel_type,
-                    }
+                    },
                 },
+                session_key=session_key,
             )
         except Exception:
             logger.exception("Error handling Slack message from {}", sender_id)