Maybe I'm missing something but does this idea need a "theory"? There's zero sideband here; everything is just context. "Injection" is just kind of baked in to the design.
I would say this method is less interesting than the question of whether one needs a discreet theory of why "prompt injections" ("malicious" frame jumps) exist or whether one should assume changing logical frame jumps are present by default in all normal human language (LLM training sets) and all the system prompts and filtering done against so called "prompt injection" are what is going be ad-hoc and without a unified theory.