The classical path for an ecommerce brand with a conversion problem used to be a retainer. Sign a three-to-six-month engagement with a CRO or frontend optimization agency, wait for the audit, wait for the experiments, wait for the rebuild, and absorb a four-figure monthly bill on top of the in-house cost you were already paying. The agency did three things — diagnosed what was broken, produced new frontend code, and instrumented the analytics to prove the lift. All three sat inside one invoice because all three required specialist hours. In 2026 those three pieces have separated. AI builders can regenerate a polished, conversion-oriented frontend from a written spec in a day. Session-replay and heatmap tools identify friction without a human analyst scrubbing through recordings. Experiment platforms run themselves. The rebuild-for-conversion project is still real work — but it is in-house work now, and the agency retainer is no longer the only viable path.…