Support custom channel assistant IDs via lead_agent (#1500)

* Support custom channel assistant IDs via lead agent

* Normalize custom channel agent names

README.md

@@ -304,7 +304,7 @@ channels:
 
   # Optional: global session defaults for all mobile channels
   session:
-    assistant_id: lead_agent
+    assistant_id: lead_agent  # or a custom agent name; custom agents are routed via lead_agent + agent_name
     config:
       recursion_limit: 100
     context:
@@ -330,12 +330,12 @@ channels:
 
     # Optional: per-channel / per-user session settings
     session:
-      assistant_id: mobile_agent
+      assistant_id: mobile-agent  # custom agent names are also supported here
       context:
         thinking_enabled: false
       users:
         "123456789":
-          assistant_id: vip_agent
+          assistant_id: vip-agent
           config:
             recursion_limit: 150
           context:
@@ -343,6 +343,10 @@ channels:
             subagent_enabled: true
 ```
 
+Notes:
+- `assistant_id: lead_agent` calls the default LangGraph assistant directly.
+- If `assistant_id` is set to a custom agent name, DeerFlow still routes through `lead_agent` and injects that value as `agent_name`, so the custom agent's SOUL/config takes effect for IM channels.
+
 Set the corresponding API keys in your `.env` file:
 
 ```bash