refactor(subagent): merge continuation control service

examples/headless-agent/cordis.yml

@@ -86,12 +86,8 @@
   config:
     providerName: fork
 
-# Continuable background children: the control service owns durable child ids
-# and Task-backed activations; the control tool registers the one global
-# `send_message` shared by both delegation tools.
-- id: subagent-control
-  name: '@deepseek-ai/dsh-subagent-control'
-
+# Continuable background children are selected per delegation tool. The
+# separately loaded follow-up tool registers the one global `send_message`.
 - id: tool-subagent-control
   name: '@deepseek-ai/dsh-tool-subagent-control'
 
@@ -100,6 +96,7 @@
   config:
     provider: spawn
     toolName: subagent
+    backgroundMode: continuable
     maxDepth: 1
 
 - id: tool-subagent-fork
@@ -107,6 +104,7 @@
   config:
     provider: fork
     toolName: subagent_fork
+    backgroundMode: continuable
     maxDepth: 1
 
 # The worker-thread workflow engine fans a model-written JavaScript script's