Engineering Liability Medicine: A Conceptual Framework for Governing Technical Debt as a Longitudinal Axis of Engineering Health

Technical debt is commonly governed as a list: items are recorded, ranked, deferred, and eventually closed. This paper argues that the list model misrepresents the phenomenon. Debt is not a to-do item, a bug, or a priority label. It is an engineering obligation gap, bound to a location in a system, legitimate at birth, charging interest only once a triggering condition expires unmet, and able to compound, propagate, entrench, transfer, and recur over a system's life. We propose Engineering Liability Medicine, a conceptual framework that elevates technical debt from a backlog concern to a governance axis peer to root cause analysis: where root cause analysis asks why a system became sick, liability medicine asks what a system carries through its life and why the burden grows heavier or lighter. The framework contributes (i) an anatomy, physiology, and pathology of debt; (ii) a lifecycle from healthy deferral through repayment, recurrence, and calibration; (iii) governance invariants, including debt removal ≠ debt repayment and unknown ≠ zero; and (iv) a projection language—two-dimensional, three-dimensional, and temporal—in which no projection may generate fact. The framework is illustrated by the debt ledger of one self-bootstrapped project (N = 1), offered as an existence proof rather than validation; no implementation is disclosed and no empirical generalisation is claimed. Version 2 adds Section 8, an illustrative N = 1 observation drawn from the project's debt ledger, and expands the Limitations accordingly. Version 1 remains available at DOI 10.5281/zenodo.22863007.