feat: Add the FDv2 data system orchestrator

[beekld]

Summary

Adds the FDv2 orchestrator, the DataSystem implementation that owns the
in-memory store and keeps it populated. It runs an initializer phase to obtain
a basis, then a synchronizer phase for ongoing changes.

The initializer phase tries each initializer in order until one produces a
basis. The synchronizer phase then runs one synchronizer at a time and rotates
between them on three triggers:

• A fallback timer advances to the next synchronizer after a sustained
  interruption.
• A recovery timer returns to the primary synchronizer after the recovery
  interval.
• A terminal error blocks a synchronizer and advances past it.

Initialization is signaled as complete on the first basis and as failed once
every source is exhausted without one, because the client's initialization path
already resolves to success or failure. Synchronizer status transitions are
logged, with interruptions at info (not repeated while ongoing) and terminal
errors at warn.

---

Note

Overview
Introduces FDv2DataSystem, the FDv2 DataSystem that owns an in-memory store and keeps it updated through initializer and synchronizer phases.

Initializer phase walks configured initializers until one returns a full basis (ChangeSet), applies it via TransactionalDataStore::apply, and signals init_complete(true) once.

Synchronizer phase runs one synchronizer at a time, passing the latest selector into next, and applies partial/full change sets as they arrive. SourceManager rotates among synchronizer factories: sustained interruption arms a fallback timer to advance to the next source; a recovery timer (when not on the prime) rewinds to the primary; terminal errors block that factory and move on. Shutdown ends the loop without a failure callback if init never completed.

Registers the module in fdv2/mod.rs and removes stale dead_code allowances on ChangeSet.selector and TransactionalDataStore now that the orchestrator consumes them. Adds broad unit/integration-style tests for rotation, timers, init signaling, and store reads.

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None changesets treated as real updates

High Severity

Any ChangeSet is treated as a basis, including ChangeSetKind::None from polling 304 and xfer-none. Those payloads carry a None selector, so the live basis is overwritten and init_complete(true) can fire with an empty store. Later next calls then omit basis, forcing full transfers instead of deltas.

Additional Locations (1)

• launchdarkly-server-sdk/src/fdv2/data_system.rs#L186-L192

 

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