Observer Requirements: Deriving the Receiver Laws from Bounded Estimation (IMM Paper 18 — Open Series)

This paper rebuilds the foundations of the RPCS-1 receiver framework (Paper 9) from the minimal requirements for there to be an observer at all. We model a bounded observer--actor that must estimate a changing environmental quantity from noisy sequential observations and act on the estimate under time constraints, and we derive each receiver control knob as a forced consequence of that setup, with optimal-setting laws obtained from standard optimality theory. Five results are registered: temporal-integration matching laws (R-1), update-elasticity matching laws (R-2), the epistemic action-rate law with a rational-freeze boundary (R-3), the joint gain--criterion optimum for the detection channel (R-4), and commitment as optimal stopping (R-5). The synthesis (R-6/T-OR-1) is the paper's principal claim: under the stated assumptions, what boundedness forces is not five independent primitives but three coupled functional blocks --- estimate, detect, commit --- of which the five RPCS-1 primitives are a parameterization. Every lemma used is standard mathematics and is credited as such; the contribution is architectural. All numerical verifications were pre-registered with fixed pass/fail criteria before data generation; three registered checks failed and their repairs or retractions are reported in full. A costed experimental program (four LLM-battery tests, total primary budget under 10) is specified, including outcomes that would count against the framework. This paper supersedes the derivation claims of Pred-09-5 and A-FIVE-1 and grades the repair ansatz A-09-1' ; it does not claim any result beyond its stated assumptions.