Allow chat history to be sent to AI engine (#6128)

# Description of Changes
Add an extra parameter to every agent to receive the conversation
history in addition to the current message. This will make it possible
to answer followup questions from the AI without needing to give full
context in your message.

engine/tests/test_user_spec_agent.py

@@ -32,7 +32,9 @@ class StubUserSpecAgent(UserSpecAgent):
             ],
         )
 
-    async def _build_edit_plan(self, user_message: str) -> EditPlanResponse:
+    async def _build_edit_plan(
+        self, user_message: str, conversation_history: list[ConversationMessage]
+    ) -> EditPlanResponse:
         return self.edit_plan
 
     async def _run_draft_agent(self, request: AgentDraftRequest, edit_plan: EditPlanResponse) -> AgentDraft:
@@ -46,7 +48,9 @@ class ClarifyingUserSpecAgent(UserSpecAgent):
     def __init__(self, runtime: AppRuntime) -> None:
         super().__init__(runtime)
 
-    async def _build_edit_plan(self, user_message: str) -> EditClarificationRequest:
+    async def _build_edit_plan(
+        self, user_message: str, conversation_history: list[ConversationMessage]
+    ) -> EditClarificationRequest:
         return EditClarificationRequest(
             question="Which pages should be changed?",
             reason="The request does not specify the target pages.",