ΣΦL Encoding: Physics-Locked Encoding and Encoded-Encoder Closure

This paper presents ΣΦL Encoding, an architecture in which content, protection, and verification collapse into the same object. Instead of encrypting hidden plaintext with a separate key, internal state is represented as derivation chains from physical premises through ΣΦL. Under invariant-preserved decoding, a malformed chain fails verification, while a valid chain is admissible physics-derived content. The paper also introduces encoded-encoder closure: the encoder itself is represented and verified under the same physics-locked structure it enforces. This closes the lens-substitution attack, where corruption of the translator would make downstream derivations faithfully wrong while appearing locally valid. The implementation appendix provides a data-only prototype encoder with chain tracing, compression, decode-as-verification, membrane checks, immutable boot signatures, and candidate lens-update verification. This record should be read as the encoding/security companion to Paper 7 and ΣΦL. It does not claim that an entire runtime is unhackable; it claims semantic unhackability of the encoding layer under invariant-preserved decoding and the stated threat model.