feat(memory): support ephemeral gateway recall context

app-instance/backend/beaver/engine/context/builder.py

@@ -112,6 +112,7 @@ class ContextBuildInput:
     current_user_input: str | list[dict[str, Any]] | None = None
     memory_snapshot: MemorySnapshot | None = None
     activated_skills: list[SkillContext] = field(default_factory=list)
+    reference_messages: list[dict[str, Any]] = field(default_factory=list)
     session_context: SessionContext | None = None
     runtime_context: RuntimeContext | None = None
     execution_context: str | None = None
@@ -221,6 +222,11 @@ class ContextBuilder:
 
         messages.extend(self.build_skill_activation_messages(build_input.activated_skills))
 
+        for message in build_input.reference_messages:
+            if message.get("role") == "system":
+                continue
+            messages.append(self._provider_history_message(message))
+
         for message in build_input.history:
             # 当前 builder 自己负责生成唯一的 system prompt。
             # 如果上游 history 已经混入 system 消息，这里要主动跳过，避免双 system。