diff --git a/agentserver/message_bus/stream_pump.py b/agentserver/message_bus/stream_pump.py
index 583c379..7773601 100644
--- a/agentserver/message_bus/stream_pump.py
+++ b/agentserver/message_bus/stream_pump.py
@@ -381,9 +381,11 @@ class StreamPump:
 
                     # === CONTEXT BUFFER: Record incoming message ===
                     # Append validated payload to thread's context buffer
+                    # The returned BufferSlot becomes the single source of truth
+                    slot = None
                     if current_thread and state.payload:
                         try:
-                            context_buffer.append(
+                            slot = context_buffer.append(
                                 thread_id=current_thread,
                                 payload=state.payload,
                                 from_id=state.from_id or "unknown",
@@ -400,16 +402,24 @@ class StreamPump:
                                 f"Thread {current_thread[:8]}... exceeded context buffer limit"
                             )
 
-                    metadata = HandlerMetadata(
-                        thread_id=current_thread,
-                        from_id=state.from_id or "",
-                        own_name=listener.name if listener.is_agent else None,
-                        is_self_call=is_self_call,
-                        usage_instructions=listener.usage_instructions,
-                        todo_nudge=todo_nudge,
-                    )
+                    # Derive metadata from slot (single source of truth)
+                    # Fall back to manual construction if no slot (e.g., buffer overflow)
+                    if slot:
+                        from agentserver.memory import slot_to_handler_metadata
+                        metadata = slot_to_handler_metadata(slot)
+                        payload_ref = slot.payload  # Same reference as in buffer
+                    else:
+                        metadata = HandlerMetadata(
+                            thread_id=current_thread,
+                            from_id=state.from_id or "",
+                            own_name=listener.name if listener.is_agent else None,
+                            is_self_call=is_self_call,
+                            usage_instructions=listener.usage_instructions,
+                            todo_nudge=todo_nudge,
+                        )
+                        payload_ref = state.payload
 
-                    response = await listener.handler(state.payload, metadata)
+                    response = await listener.handler(payload_ref, metadata)
 
                     # None means "no response needed" - don't re-inject
                     if response is None: