Get rid of LLMContext.get_messages_for_persistent_storage().

The reason for its `system_instruction` argument was to support usage with LLMs where you might pass the system instruction as a parameter to the `LLMService` rather than specifying it in the context.

But as I thought about it more I became unconvinced that the `system_instruction` argument was really beneficial:

- If you specified your system instruction in your context in the first place, it'll still be there when you read messages for persistent storage
- If you didn't specify your system instruction in the context and instead passed it in as an `LLMService` parameter, you most likely *don't* want it to be in the context when you read messages for persistent storage
- ...and if you really really do need to inject it at the start of the context, it's quite easy to do anyway

And if we remove the `system_instruction` argument from `get_messages_for_persistent_storage()`, then it's essentially just `get_messages()`.

examples/foundational/20a-persistent-context-openai.py

@@ -67,11 +67,11 @@ async def save_conversation(params: FunctionCallParams):
     timestamp = datetime.now().strftime("%Y-%m-%d_%H:%M:%S")
     filename = f"{BASE_FILENAME}{timestamp}.json"
     logger.debug(
-        f"writing conversation to {filename}\n{json.dumps(params.context.get_messages_for_persistent_storage(), indent=4)}"
+        f"writing conversation to {filename}\n{json.dumps(params.context.get_messages(), indent=4)}"
     )
     try:
         with open(filename, "w") as file:
-            messages = params.context.get_messages_for_persistent_storage()
+            messages = params.context.get_messages()
             # remove the last message, which is the instruction we just gave to save the conversation
             messages.pop()
             json.dump(messages, file, indent=2)

examples/foundational/20c-persistent-context-anthropic.py

@@ -68,12 +68,11 @@ async def save_conversation(params: FunctionCallParams):
     timestamp = datetime.now().strftime("%Y-%m-%d_%H:%M:%S")
     filename = f"{BASE_FILENAME}{timestamp}.json"
     logger.debug(
-        f"writing conversation to {filename}\n{json.dumps(params.context.get_messages_for_persistent_storage(), indent=4)}"
+        f"writing conversation to {filename}\n{json.dumps(params.context.get_messages(), indent=4)}"
     )
     try:
         with open(filename, "w") as file:
-            # todo: extract 'system' into the first message in the list
-            messages = params.context.get_messages_for_persistent_storage()
+            messages = params.context.get_messages()
             # remove the last message, which is the instruction we just gave to save the conversation
             messages.pop()
             json.dump(messages, file, indent=2)

examples/foundational/20d-persistent-context-gemini.py

@@ -86,11 +86,11 @@ async def save_conversation(params: FunctionCallParams):
     timestamp = datetime.now().strftime("%Y-%m-%d_%H:%M:%S")
     filename = f"{BASE_FILENAME}{timestamp}.json"
     logger.debug(
-        f"writing conversation to {filename}\n{json.dumps(params.context.get_messages_for_persistent_storage(), indent=4)}"
+        f"writing conversation to {filename}\n{json.dumps(params.context.get_messages(), indent=4)}"
     )
     try:
         with open(filename, "w") as file:
-            messages = params.context.get_messages_for_persistent_storage()
+            messages = params.context.get_messages()
             # remove the last message (the instruction to save the context)
             messages.pop()
             json.dump(messages, file, indent=2)

examples/foundational/20e-persistent-context-aws-nova-sonic.py

@@ -77,7 +77,7 @@ async def save_conversation(params: FunctionCallParams):
     filename = f"{BASE_FILENAME}{timestamp}.json"
     try:
         with open(filename, "w") as file:
-            messages = params.context.get_messages_for_persistent_storage()
+            messages = params.context.get_messages()
             # remove the last few messages. in reverse order, they are:
             # - the in progress save tool call
             # - the invocation of the save tool call