Google deindexed half of my Next.js site. Here's the four-phase recovery.

I run a side project: a gas price finder that's mostly programmatic content. Roughly 33,620 ZIP code pages plus a few hundred state and city pages, all built on Next.js 15 with ISR. It runs on Vercel, fronted by Cloudflare for DNS. For about eight months it was indexing fine. Traffic was small but growing. Then on April 11 I checked Google Search Console and saw something I'd never seen at this scale: 87 URLs flagged as "not found (404)," 61 flagged as "soft 404," and a chunk of others sitting i