Refine discussion closure messaging

plans/CSM.md

@@ -255,10 +255,11 @@ After callback:
 [Discussion Idle]
 
 No agent responded in the latest discussion round.
-If the discussion goal has been achieved, the initiator should now:
+If the discussion goal has already been achieved, the initiator should now:
 1. write the discussion summary to a file in the workspace
 2. call discuss-callback with the summary file path
 
+This reminder does not mean the discussion was automatically summarized or closed.
 If more discussion is still needed, continue the discussion in this channel.
 ```
 
@@ -284,6 +285,7 @@ If more discussion is still needed, continue the discussion in this channel.
 This discussion channel has been closed.
 It is now kept for archive/reference only.
 Further discussion in this channel is ignored.
+If follow-up work is needed, continue it from the origin work channel instead.
 ```
 
 这部分实现明确采用已有“在指定 session 上临时覆盖为 no-reply 模型”的方式，而不是修改 Agent 的全局默认模型。