Mock interview: feature flags at Switchyard

A full 50-minute staff-level model interview: Tejas asks where evaluation happens before anything else, proves with numbers that SDKs must evaluate locally and that the control plane is tiny next to the data plane, makes bucketing sticky and identical in every language, streams deltas through the edge, budgets and proves a 5-second kill switch, refuses to trust last year's empty ruleset, protects experiments from reallocation, late data and sample ratio mismatch, contains a leaked SDK key, and turns a bank's demand for its own everything into a dedicated cell, BYOK and a relay proxy.