Event Restricted Temporality (ERT): Definitions, Typing Rule, and Domain Gates — Specification v2.1

Event‑Restricted Temporality (ERT) is a domain‑of‑applicability framework that specifies when temporal parameters and predicates are well‑typed in physical (physics) description. ERT distinguishes three descriptive regimes—Structural, Retentive, and Event—and introduces an event‑license functional 𝒜D, defined relative to an admissible control set 𝒞, to determine whether time‑talk (t, ∂/∂t, before/after, time‑ordering) is admissible on a given description. The core rule of the framework (the Echo typing rule) states that temporal operators are admissible on a description D if and only if 𝒜D > 0. Structural and Retentive descriptions, for which 𝒜D = 0, are nontemporal by type: time‑based questions on such descriptions are not unanswered but ill‑posed (domain errors). A control‑relative robustness threshold 𝒜* distinguishes fragile from robust event‑license within the Event regime. This specification presents the canonical definitions of ERT, including the event‑license functional, the robustness threshold, the Eight Doors of Time (domain gates governing temporal admissibility), diagnostic failure modes, worked minimal examples, and a formal application protocol. ERT does not propose new dynamics or modify existing physical theories; rather, it constrains the domain on which time‑parametrised description is well‑typed. This document is a citable definitional specification (reference standard), not a research article. It provides stable terminology, symbol conventions, and typing rules for use in foundational analysis and applications. Extensions and applications may be developed separately but must cite this specification as the definitional reference.