Right now, our APIs use a mix of pointers and direct object references. We should be more uniform in our approach here. Suggested guidelines:

• For structs representing messages (e.g., Welcome, Commit), fields are by value, except when optional
• For other structs (e.g., State, HPKEPrivateKey), fields are as produced / passed to APIs, thus usually pointers
• Fields in messages are by value, except when optional
• Objects are passed to/from API methods by reference (as pointers)