Replit attacks the assumption that autonomous code genuinely works by building a self-testing reflection loop that drives a real browser to catch the 'Potemkin interface' — code that looks complete but fails when actually used.

Replit concentrated its work on whether autonomously generated code genuinely works using a verification loop built into the agent itself. Replit's Agent 3 runs what the company calls a reflection loop. The agent generates code, runs it, tests the result, and repairs failures, repeating that cycle until the tests pass. This loop is reliable because of how the testing is done. Replit built a REPL-based verification system that runs code immediately and pairs that execution with a real browser it drives automatically, so it can click buttons, submit forms, and check data the way a user would. The specific problem this approach targets has a memorable name inside Replit: the Potemkin interface. It is basically a feature that looks complete on screen yet fails the moment it is used. Catching that class of error is what allows the agent to run on its own for more than 200 minutes at a stretch, a large increase over the roughly 20 minutes of its predecessor. ... A testing subagent follows a simple cycle of taking an action, observing the result, and repeating. When it finishes, it returns a summary to the main agent describing what works and what broke. This multi-hundred-step testing costs a median of roughly twenty cents per session and runs several times faster and more cheaply than relying on general-purpose computer-use models.

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