Myself specifically, I have a /code folder without about 10 copies of our codebase, each running their own claude sessions & git branch. Then, I have 10 terminal branches. I spend a ton of time planning out & specing the problem with claude, to be as specific as possible and be as constrained as possible so it cannot go on side-quests. I use Opus 5.5 on High effort. That's just on my laptop with what I can mentally cope with day to day. Then we have some other automatic ai goodies running within our custom agent framework that runs within our platform that also helps. Then for apps, I basically plug in multiple phones into my laptop with usb (and emulators if I really need to), and claude can fully drive the ui and testing on the phones via adb as an example. Even on linux/fedora/kde it can drive UI apps a and take screenshots and fix things properly etc. It can ingest all logs & debug chains, so it absolutely flies through its task.

Before we started this journey (about a year ago), we spent a ton of time cleaning up our codebase, splitting large files (10K+ lines) into files that are no more than 2K lines, things like that. Then we let claude scan our important files and summarize them, add comments for future claude sessions. So we've let it built up tribal knowledge per file and the reasons for things to exist. We tell it all about our operating environment, the country and legal framework etc, so every little piece helps it stay honest and on track.

So to start, do something simple like: Scan the files in this folder for database code and check for queries that loads the entire result set into memory and/or queries that loads all columns. Suggest which queries we can filter better or reduce columns being transferred. Once done, also check real db row counts, compare them with the queries in these files and check if they might benefit from an index or partitioning/sharding. Also check for queries that loads data but their results are not used. Don't make changes yet, just do a deep investigation and report back. Feel free to spin up muliple agents to batch the scans.

edit: it goes without saying you need a language with strict typing and a good compiler (we use dotnet). Doing this on python/javascript would be a nightmare.