San Francisco backend startup Convex closed a $57 million Series B led by Insight Partners, with Etna Labs, Spark Capital, a16z, and Justin Kan joining. It sells an ACID, TypeScript end-to-end stack with sandboxed components so coding agents cannot silently corrupt data as they often do on loosely typed databases. Convex says millions of instances already run in production and will use the round for hiring plus deeper agent tooling. Why it matters: as agents ship more of the codebase, the durable layer becomes the product. Caveat: reliability claims lean on Convex's own tests, and rival backend vendors are racing to the same narrative.