I used all of my credits working on a PySide QT desktop app last weekend. What worked:

I first had Claude write an E2E testing framework that functioned a lot like Cypress, with tests using element selectors like Jquery and high level actions like 'click' with screenshots at every step.

Then I had Claude write an MCP server that could run the GUI in the background (headless in Claude's VM) and take screenshots, execute actions, etc. This gave Claude the ability to test the app in real time with visual feedback.

Once that was done, I was able to run half a dozen or more agents at the same time running in parallel working on different features. It was relatively easy to blow through credits at that point, especially since I think VM times counts so whenever I spent 4-5 min running the full e2e test suite that cost money. At the end of an agents run, I'd ask them to pull master and merge conflicts, then I'd watch the e2e tests run locally before doing manual acceptance testing.