feat: open LargeSmtForest backend API for external implementations

CHANGELOG.md

@@ -5,6 +5,7 @@
 #### Changes
 - `FastProcessor` `restore_call_state()` and `restore_context()` now return `OperationError::Internal` instead of panicking on empty stacks ([#3371](https://github.com/0xMiden/miden-vm/pull/3371), fixes [#3296](https://github.com/0xMiden/miden-vm/issues/3296)).
 
+- Opened the `LargeSmtForest` backend API for external implementations: made `LineageMutation::new` and `AppliedLineageMutation::new` public and added `LineageId::as_bytes`.
 - [BREAKING] Renamed module and kernel metadata APIs from `ModuleInfo`/`Kernel` to `ModuleDescriptor`/`KernelDescriptor`, including matching module descriptor method names ([#3356](https://github.com/0xMiden/miden-vm/pull/3356)).
 - Aligned workspace crate versions at `0.28.0`, except `midenc-hir-type`, so VM and crypto crates release as one version line.
 - Imported the Miden crypto crates, benches, fuzz targets, and Wycheproof tests into this workspace ([#3366](https://github.com/0xMiden/miden-vm/pull/3366)).

crates/crypto/src/merkle/smt/large_forest/root.rs

@@ -37,6 +37,14 @@ impl LineageId {
     pub fn new(bytes: [u8; 32]) -> Self {
         Self(bytes)
     }
+
+    /// Returns the raw bytes of the lineage ID.
+    ///
+    /// This is primarily useful for [`Backend`](super::backend::Backend) implementations that
+    /// need to persist lineage identifiers.
+    pub fn as_bytes(&self) -> &[u8; 32] {
+        &self.0
+    }
 }
 
 impl core::fmt::Display for LineageId {

crates/crypto/src/merkle/smt/large_forest/utils.rs

@@ -108,9 +108,10 @@ pub struct LineageMutation {
 impl LineageMutation {
     /// Constructs a lineage mutation.
     ///
-    /// This constructor is crate-private because callers must not be able to fabricate mutation
-    /// metadata that is inconsistent with the backend-prepared data in an [`SmtForestMutationSet`].
-    pub(crate) fn new(
+    /// This is intended for [`Backend`] implementations returning computed mutations. The
+    /// metadata must stay consistent with the backend-prepared data in the corresponding
+    /// [`SmtForestMutationSet`].
+    pub fn new(
         lineage: LineageId,
         old_version: Option<VersionId>,
         new_version: VersionId,
@@ -207,10 +208,10 @@ pub struct AppliedLineageMutation {
 impl AppliedLineageMutation {
     /// Constructs an applied lineage mutation.
     ///
-    /// This constructor is crate-private because backend implementations must keep the returned
-    /// history payload consistent with the prepared mutation data they just applied.
+    /// [`Backend`] implementations must keep the returned history payload consistent with the
+    /// prepared mutation data they just applied.
     #[allow(clippy::too_many_arguments)]
-    pub(crate) fn new(
+    pub fn new(
         lineage: LineageId,
         old_version: Option<VersionId>,
         new_version: VersionId,