I've stopped trying to achieve general "memory". I just ask the agent to thoroughly, but concisely, document each project. If it writes developer documentation and a development plan/roadmap, as though a person was going to have to get up to speed and start working on the project, it provides all the information the agent needs tomorrow or next week to pick up where we left off.
The agent is not my friend. I don't need it to remember my birthday or the nasty thing I said about React last week. I need it to document what anyone, agent or human, would need to know to get productive in a particular repo, with no previous knowledge of the project.
Good, concise, developer and user documentation and a plan with checklists solves every problem people seem to think "memory" will solve: It tells the agent what tech stack to use (we hashed it out in planning), it tells it what commands it needs to run and test the app, it covers the static analysis tools in use (which formalizes code style, etc. in a way a vague comment I made a month ago cannot), and it is cheap. Markdown files are the native tongue of agents. No MCP, no skills, no API needed. Just read the file. It works for any agent, any model, and any human just getting started with the project.
Basically, I think memory makes agents dumber and less useful. I want it to focus on the task at hand.