[keelerm84]

FeatureStore#upsert and FeatureStore#delete must now return true when the
store applies the write, and false when the store already has an item with
the same or a higher version. FeatureStoreCore#upsert_internal, used with
CachingStoreWrapper, must return the same boolean instead of the final item.

Before this change, the SDK sent flag change events after every upsert or
delete from the data source, even when the store rejected a stale write. A
repeated or out-of-order update therefore produced change events for flags
that did not change. The SDK now updates its dependency tracking and sends
change events only when the store reports that it applied the write.

When a core reports that it did not apply an upsert, CachingStoreWrapper
reads the current item from the core and caches it. This matches the Go
SDK's persistent store wrapper.

Custom store implementers:

• A FeatureStore that returns nil or another falsy value from upsert or
  delete stops flag change events for those writes. The default methods in
  LaunchDarkly::Interfaces::FeatureStore return nil, so implementations
  must return the result explicitly.
• A FeatureStoreCore must return true or false from upsert_internal. The
  wrapper no longer accepts the final item as the return value.

---

Note

Overview
Breaking change: FeatureStore#upsert and #delete (and FeatureStoreCore#upsert_internal) now return true when the write is applied and false when the store already has the same or a newer version, instead of returning void or the final entity.

The data source UpdateSink uses that signal so dependency tracking and flag change listeners run only after a successful store write. Duplicate or out-of-order streaming updates no longer emit spurious change events.

Built-in stores (in-memory, Redis, DynamoDB, Consul) and CachingStoreWrapper were updated: on a rejected upsert, the wrapper re-reads the current item from the core and refreshes the cache (aligned with the Go SDK), rather than caching the stale payload. DynamoDB no longer performs an extra read when a conditional write fails.

Custom store authors must return explicit booleans; default interface stubs still return nil, which is treated as falsy and suppresses change events.

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