Every agent platform ships memory now. Persistence across sessions went from a trick to a checkbox sometime this year, and I expected that to settle the question. It didn't. My agents remembered plenty. They just never remembered anything useful, and the first time I audited the store I found out why: the memory was filed like a library and read like a headline.
Here is the mechanism that bit me. A memory store has two layers, an index file that loads into every session, and a body file per memory that loads only if something sends the agent to read it.
memory/
├── MEMORY.md the index: one line per memory, loaded
│ into every session
