Audit negative variant checks when extending an experiment

When adding a treatment that reuses an existing UI, audit backend negative variant checks as well as the renderer and telemetry allowlists. A check such as “version is not the existing treatment” can silently classify the new treatment as legacy even after its type and rendering support compile successfully. If the backend converts normal intermediate progress into a completion attempt, this can trigger premature escalation. Test the new variant at that persistence boundary, preserving the distinction between unfinished evidence and explicit final failure. This applies to shared-flow treatments; materially different verification policy still needs its own contract.

Applies when: extending experiment variants across client presentation and incremental backend submission. Keywords: experiment variant enum negative comparison legacy backend escalation progress