When Specifications Are Only Partially Formalized: Towards Reliable Clinical Reasoning

Modern coding agents succeed when their environments provide reliable, machine-checkable feedback that can constrain model behavior. Software development exemplifies this regime: executable artifacts, compilation, testing, and execution create dense feedback signals that make actions verifiable and correctable. Clinical reasoning presents a different challenge. Clinical guidelines provide rich specifications, but only part of their content can be converted into machine-checkable structure, while the remainder requires context-dependent semantic judgment. The challenge is therefore to operationalize the executable portions of clinical specifications without forcing inherently semantic decisions into rigid rules. We introduce GEVHarness, a guideline harness for reliable clinical reasoning under partially formalized specifications. GEVHarness partitions guidelines into machine-checkable structure, which receives deterministic runtime authority over explicit state, and contextual judgments, which remain model-mediated. The model interprets evidence, while the runtime decides what follows, withholds commitment when evidence is incomplete, and makes every trajectory verifiable by replay. Across eight frozen benchmark panels spanning workflow control, open clinical reasoning, and evidence control, GEVHarness is the strongest interface among matched text and model-guided structured baselines for both evaluated backbone blocks; it improves the cases whose correct decisions change with evidence, and Controlled interventions further show that the value of formalization depends not only on how much of the specification is executable, but on where runtime authority is placed. These results position partially formalized specifications as a distinct inference-harness regime: a specification need not be a complete execution oracle to govern inference. More broadly, clinical reasoning exposes a persistent tension between semantic flexibility and executable reliability; GEVHarness offers one concrete step toward understanding how models, specifications, and runtimes should share control.