The encoding/decoding model of communication emerged in rough and general form in 1948 in Claude E. Shannon’s “A Mathematical Theory of Communication,” where it was part of a technical schema for designating the technological encoding of signals. Gradually, it was adapted by communications scholars, most notably Wilbur Schramm, in the 1950s, primarily to explain how mass communications could be effectively transmitted to a public, its meanings intact by the audience (i.e., decoders). – Wilbur, Schramm (1954). The process and effects of mass communication. Urbana, Illinois: University of Illinois Press.
The “Claude Code” naming is something I’ve heard on Reddit (no source link).
Encoding and decoding already existed long before that - when you write something down you’re encoding an abstract signal using marks on a page, and more clearly, telegraphy used a variety of encoding schemes. Shannon gave the subject a rigorous treatment though and established important theorems.