SepRAG BET 1 (finding): incremental reindex WINS the high-recall tier vs reuse + periodic rebuild

crates/ruvector-diskann/Cargo.toml

@@ -11,6 +11,8 @@ description = "DiskANN/Vamana — SSD-friendly approximate nearest neighbor sear
 default = []
 gpu = []  # Feature flag for GPU acceleration (CUDA/Metal stubs)
 simd = ["simsimd"]
+# BET 1 (ADR-200): fixed-topology reuse + periodic rebuild under metric drift.
+reuse-under-drift = []
 
 [dependencies]
 memmap2 = { workspace = true }

crates/ruvector-diskann/src/graph.rs

@@ -215,7 +215,13 @@ impl VamanaGraph {
         self.greedy_search_fast(vectors, query, beam_width, &mut visited)
     }
 
-    fn robust_prune(
+    /// α-robust pruning of a candidate set down to `max_degree` diversified out-edges.
+    ///
+    /// Exposed at crate visibility (no logic change) so the `reuse-under-drift`
+    /// incremental-reindex path ([`crate::reuse::IncrementalIndex`]) can refresh a single
+    /// displaced node's neighbourhood without a full rebuild. Used internally by
+    /// [`VamanaGraph::build`].
+    pub(crate) fn robust_prune(
         &self,
         vectors: &FlatVectors,
         node: u32,

crates/ruvector-diskann/src/lib.rs

@@ -15,7 +15,12 @@ pub mod error;
 pub mod graph;
 pub mod index;
 pub mod pq;
+/// Fixed-topology reuse + periodic rebuild under metric drift (BET 1, ADR-200).
+#[cfg(feature = "reuse-under-drift")]
+pub mod reuse;
 
 pub use error::{DiskAnnError, Result};
 pub use index::{DiskAnnConfig, DiskAnnIndex};
 pub use pq::ProductQuantizer;
+#[cfg(feature = "reuse-under-drift")]
+pub use reuse::{DriftingIndex, IncrementalIndex, RebuildPolicy, RecallTrigger};