feat(kms): restore local backend key material from sealed backup bundles

The consumer side of the Local bundle export, as a four-phase protocol:

- Dry-run: full in-memory bundle decode (digest and AEAD verification of
  every artifact), KDF-drift detection against the compiled-in
  derivation, deployment and injected-generation checks (strictly lower
  is rejected, equal stays allowed for repeated drills), master-key
  verifier check, and target conflict enumeration - with zero writes.
- Staging: artifacts are committed durably into the .restore-staging/
  subdirectory (invisible to the backend's key scan and orphan-temp
  matcher) and every record is decryption-probed with the derived
  master key both in memory before staging and again from the staged
  bytes.
- Commit marker + cutover: the durably published .restore-commit.json
  marker is the single commit point; cutover publishes staged files via
  link_durably (salt first, keys after), then durably removes the
  marker and drops staging.
- Crash re-entry: before the marker the target top level is untouched
  and a re-run starts over; with the marker published, backend startup
  fails closed and a re-run with the same bundle rolls forward while
  abort_local_restore rolls back. Every interruption converges to the
  complete old or complete new state.

Restore never goes through LocalKmsClient::new (which would mint a
fresh salt); the only write mode is the explicit
restore-into-empty-target policy, where an orphan salt or a foreign
marker already counts as non-empty. The bundle source stays strictly
read-only.

Refs rustfs/backlog#1572

crates/kms/src/backup/mod.rs

@@ -16,9 +16,10 @@
 //!
 //! The contract side defines the versioned backup manifest, the per-backend
 //! responsibility matrix, typed failure modes, and the restore dry-run
-//! report. [`local_export`] implements the producer side for the Local
-//! backend as a crate-internal API; restore orchestration and the admin API
-//! build on these pieces in follow-up changes.
+//! report. [`local_export`] implements the producer side and
+//! [`local_restore`] the consumer side for the Local backend as
+//! crate-internal APIs; the admin API builds on these pieces in follow-up
+//! changes.
 //!
 //! # Bundle model
 //!
@@ -51,6 +52,7 @@ mod capability;
 mod dry_run;
 mod error;
 pub mod local_export;
+pub mod local_restore;
 mod manifest;
 
 pub use capability::{AtRestProtection, BackupBackendKind, BackupResponsibility};
@@ -62,6 +64,10 @@ pub use local_export::{
     BackupKek, LOCAL_BUNDLE_MANIFEST_FILE, LocalBackupExportRequest, decrypt_bundle_artifact, export_local_backup,
     read_local_bundle_manifest,
 };
+pub use local_restore::{
+    LocalRestoreReport, LocalRestoreRequest, RestoreConflictPolicy, abort_local_restore, dry_run_local_restore,
+    restore_local_backup,
+};
 pub use manifest::{
     AeadAlgorithm, ArtifactDescriptor, ArtifactKind, BackupKekDescriptor, BackupManifest, CompletenessState, ContentDigest,
     DigestAlgorithm, LocalKdfDescriptor, LocalKeyDerivation, ReservedSlot,