Crypto-agility guides

Crypto-agility is the property that lets you replace a cryptographic algorithm without re-architecting the system around it. What it means concretely, the anti-patterns that block it, and why it is the real deliverable of a post-quantum migration.

The concrete patterns that make an algorithm a replaceable component: runtime negotiation, a provider abstraction, config-driven selection, self-describing versioned formats, size-agnostic storage, and automated rotation. The engineering behind agility, not the argument for it.