For macOS, generically, you can run `screencapture -o -l $WINDOW_ID output.png` to screenshot any window. You can list window IDs belonging to a PID with a few lines of Swift (that any agent will generate). Hook this up together and give it as a tool to your agents.

for anything web related, simply with the chrome claude plugin. then claude code can control the browser (and 'see' what's showing),