v2.9.0

Added

• FeatureflipClient.onUpdate(FlagUpdateListener) — subscribe to flag-configuration changes. The listener is called with the flag keys whose evaluated value may have moved, batched into one call per update, and the returned action unsubscribes (idempotently; subscriptions are also dropped when the client is closed). Brings Java level with the JS, Python and Go SDKs, and is what lets the OpenFeature provider emit PROVIDER_CONFIGURATION_CHANGED. (#1867)

  The reported set is deliberately wider than "flags whose own config changed", because two kinds of movement leave no trace on the flag that moved. A segment edit changes what a rule matches without touching — or versioning — any flag that references it. A prerequisite toggle bumps only the prerequisite's version, while every dependent flips to its off variation with PREREQUISITE_FAILED. Both are followed, the second transitively, so a listener that re-reads what it is told about sees every value that actually changed.

  The initial flag load does not fire — a cold start is not a change — and neither does a snapshot identical to the one held. That second point is load-bearing rather than an optimization: the store is handed a full snapshot on every poll tick and on every SSE reconnect, so without the comparison a listener would fire once per poll interval forever. Comparison is structural over the serialized configuration rather than a version check, since a segment edit moves a flag's value without moving its version.

• FeatureflipClient.jsonVariationDetail(key, context, defaultValue, type) — the detail counterpart of jsonVariation. Until now JSON was the one flag type whose evaluation reason, rule id and served variation key were unreachable: every other type had a *VariationDetail twin and JSON did not.

  Passing Object.class reads a value without asserting its type, yielding the plain Java shapes Jackson produces (Map, List, String, Integer, Double, Boolean). That form cannot fail as a type mismatch, which is what lets a caller — the OpenFeature provider being the first — distinguish a genuine evaluation error from a value of the wrong type. The typed accessors fold both into ERROR.

Fixed

• The README's quickstart did not compile. It reached for EvaluationContext.of(...), a factory this SDK has never had, in three of its examples — including the very first one — so anyone copying the getting-started snippet hit cannot find symbol before they hit anything else. All three now use EvaluationContext.builder(userId).build(), which is what the API actually offers.