feat(plugins): add public subagent lifecycle API

hermes_cli/plugins.py

@@ -344,6 +344,7 @@ class PluginContext:
         self._manager = manager
         # Lazy-built host-owned LLM facade — see ctx.llm property below.
         self._llm: Any = None
+        self._subagent_lifecycle: Any = None
 
     # -- host-owned LLM access ----------------------------------------------
 
@@ -364,6 +365,22 @@ class PluginContext:
             self._llm = PluginLlm(plugin_id=plugin_id)
         return self._llm
 
+    @property
+    def subagent_lifecycle(self) -> Any:
+        """Return the public, plugin-safe subagent lifecycle service.
+
+        The service only resolves the active host-owned parent agent when a
+        child is launched. Plugins receive serializable handles and immutable
+        snapshots; they never receive a live agent or a private registry.
+        """
+        if self._subagent_lifecycle is None:
+            from agent.subagent_lifecycle import SubagentLifecycleService
+            self._subagent_lifecycle = SubagentLifecycleService(
+                lambda: getattr(self._manager._cli_ref, "agent", None)
+                if self._manager._cli_ref is not None else None
+            )
+        return self._subagent_lifecycle
+
     # -- profile awareness --------------------------------------------------
 
     @property