FA-74055 / Feature flag rollout bucketing / Member archive

Sticky variant persistence: Traffic exclusion erases the stored assignment · case 05

Temporarily shrinking traffic loses users' history, so they are reshuffled when traffic returns.

Member previewVariant 5 · 3 implementations · 8 checks per implementation

Case contract

stored is None or {variant, version}. A stored record is honoured (reason sticky, record unchanged) only if its version equals the current experiment version and its variant is still active; this takes precedence over traffic exclusion. Otherwise a None bucket_variant means excluded and the stored record is kept untouched; else the bucketed variant is assigned and a new record {variant, version} is returned. Return [variant, reason, record].

Why this case matters

Sticky bucketing keeps users on one arm across sessions; stale or retired records must not leak.

One recorded failure

Sample boundary fixture

This sample comes from the broken implementation of a controlled reproducer.

Boundary fixture	Actual	Expected	Outcome
exclusion keeps the stored record	`[null, "excluded", null]`	`[null, "excluded", {"variant": "c", "version": 1}]`	Failed

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