Note

Medium Risk
Changes signature verification and signed-payload derivation for remote config (security-sensitive), though behavior is heavily covered by tests; atomic file writes are a low-risk infrastructure tweak.

Overview
Adds remote config persistence via RemoteConfigDiskCache (remote_config.json manifest/topic blob refs) on top of SynchronizedLargeItemCache, with read/write error logging.

Enables response signature verification for .remoteConfig (and keeps it for reward verification): a pluggable ResponseSignatureContextProvider lets verification use endpoint-specific signed bytes and request-body inputs. Remote config signs the first RC Container element’s stored checksum (not the full body), omits the POST body from signature params, and treats 204 as a nil response message. RCContainer.ElementParser supports parsing only that first element before full decode. Failures to build the signed payload are logged and counted as verification failures.

getRemoteConfig now returns RemoteConfigFetchResult (optional RCContainer + VerificationResult) instead of a bare container. Shared FileManager.saveData sync writes use .atomic for safer overwrites (relevant to manifest cache).

Tests cover disk cache, atomic overwrite, HTTP path flags, backend fetch results, and extensive remote-config signature scenarios (including 204 and enforced mode).

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