How did the capability leap in the second half of 2025 overcome these bottlenecks?

Frontier models like Opus 4.5 brought four key improvements: autonomous debugging via runnable environments, better requirement-to-implementation translation with tests, internalization of engineering norms through Skill files, and general Computer Use ability (terminal, browsing, GUI). These allow humans to step back from line-by-line review and instead focus on setting rules, accepting results, and spot-checking key nodes, enabling true parallel development.