> readable files that the model initializes from every run

this is how AGENTS.md et al. are supposed to work, you can include many more things, like ...

> Append-only logs, rules, inventories, histories

I include open terminals and files for example, these may make it into the system prompt. The same problem arises here, how much and when. Same story for tools, mcp, skills.

> Without persistent state

There are a lot of different ways people are approaching this. In the end, you are just prewarming a cache (system prompt). The next step is to give the agent control over that system prompt towards self-controlled / dynamic context engineering.

You, increasingly in collaboration with an agent, are doing context engineering. One can take the analogy towards a memory or knowledge hierarchy. You're also going to want a table of contents or librarian (context collecting subagent or phase, search, lots of open design space here)