Adds the third replicator sibling next to Replicator.SqlServer and
Replicator.AkkaDotNet: the central-hosted gRPC secrets hub. This commit is
scaffold only -- project, wire contract, solution wiring -- no service or
client implementation.
The proto mirrors exactly the read half of ISecretReplicationHub
(GetManifestAsync, GetManyAsync). ApplyReplicatedAsync is deliberately NOT
mirrored: in this topology every update originates at central and a site node
is a strict follower, so the narrow contract IS the enforcement -- with no
write RPC on the wire, a mis-wired or compromised site node has no way to push
a row into the hub regardless of what its authorization allows.
Messages are hand-written mirrors of StoredSecret and SecretManifestEntry
rather than serializations of the domain types, following the Akka
replicator's SecretRowDto precedent: the trust boundary stays structural, and
a field added to StoredSecret later cannot start crossing the network merely
by existing. Timestamps are ISO-8601 "O" strings (not google.protobuf.
Timestamp, which cannot round-trip a DateTimeOffset's offset) so a relayed row
is byte-identical to the one central holds; nullable .NET fields use proto3
explicit presence so null and empty string stay distinguishable.
Grpc 2.76.0 / Google.Protobuf 3.34.1 match what ScadaBridge, OtOpcUa and the
sibling ZB.MOM.WW.LocalDb libraries already resolve, so a consumer taking both
gets one Grpc rather than a downgrade warning.
Claude-Session: https://claude.ai/code/session_014WNM4vjoVksyyBraTXSZE1
Joseph Doherty
5fd7bf524a