If you run multiple processes (e.g. a cron that runs ctx sync while another sync or a long ctx serve mcp is also writing), you still only get one writer at a time at the SQLite level. We recommend not overlapping writers across processes — e.g. cron that runs sync every N hours and doesn’t start the next run until the previous one has finished (or use a lockfile). Our deployment doc says: if you see "database is locked", ensure only one ctx sync runs at a time. So: WAL is on and does what you’d expect; multi-process write contention is avoided by design (one sync at a time / no overlapping cron invocations, etc).
I might add configurable vector storage later (e.g. plug in something else for the embedding index), but I’m still not sure I need or want it. I like keeping the stack opinionated toward SQLite — one file, one binary, no extra services — so that’s the default for the foreseeable future.