The horror!
On macOS my environment is Sublime Text as editor, iTerm as terminal. I open two full screen iTerm windows of four panes each, start Claude Code Opus 4 and type "just task" in each pane. CLAUDE.md tells the session to run this justfile command and follow the directions, which generally include instructions to continue by doing "just task" again. Each session may edit its <file>.c and <file>.h but not shared headers; if it has a problem with this I touch STOP in the task directory, the other sessions eventually are told to wait, and then the trouble child session can edit what it wants.
I'm sure in a few years AI will read and fix my 57 C file code base all at once, but for now this workflow has proved invaluable.
The irony? This is the dumbest parallel task manager imaginable yet it works. And our code base has a similar feel: The storage management is a set of fixed sized stacks that outperformed malloc() by 4x back in the day. Etc. Etc.
I learned this gift from my Dad. He devised the Bayer filter for digital photography back in 1974, it looks like ten minutes work (it wasn't) but we're still using it.