Invariant-Closed System Design (ICSD)

Invariant-Closed System Design (ICSD) defines an architectural principle for building systems in which all representable states are valid and compliant by construction. Rather than relying on runtime detection, validation, or remediation of invalid or abusive behaviour, ICSD ensures that invalid states are structurally unrepresentable through constrained state models, invariant-bound transitions, and authority-anchored truth sources. This document introduces the ICSD concept, its core properties, design trade-offs, and applicability to compliance-critical domains such as payroll, taxation, financial reporting, and regulated infrastructure. It defines the current architectural and semantic baseline for the ICSD portion of the suite. This document is part of an experimental, research-oriented Independent Stream suite. It defines the current normative baseline for trust objects, validation rules, and security semantics within its scope. Hard interoperability is expected for shared object semantics and validation rules. Full wire-level, clustering, and proof-family interoperability is not claimed everywhere yet; the remaining details are intentionally profile-defined or deferred where companion work has not yet closed them.