PiPNN 3/6: add core graph construction

[SeliMeli]

Adds provider-independent PiPNN partition, leaf-build, direct-candidate, and finalization stages.

Review key points

• Core boundary is MatrixView + graph policy + caller-owned Rayon pool.
• Partition owns stage-specific config and deterministic seed derivation.
• Leaves and scratch follow ownership/MapInit; no TLS, RefCell, providers, start points, or serialization.

Stack 3/6: #1288 → #1291

[Copilot]

Pull request overview

This PR introduces the “core” PiPNN build pipeline in the diskann-pipnn crate, wiring together deterministic partitioning, leaf-local candidate construction, and final pruning into a public build_graph API with a validated build context.

Changes:

• Adds PiPNNConfig validation and a PiPNNBuildContext that binds PiPNN policy to DiskANN graph pruning policy and a caller-owned Rayon thread pool.
• Implements the three main stages: partitioning (partitioning.rs), leaf candidate construction (leaf_build.rs), and final pruning via shared Vamana robust prune (finalization.rs).
• Adds comprehensive unit/integration tests and a Criterion benchmark for core scenarios; updates dependencies, lockfile, and mutation-test exclusions.

Reviewed changes

Copilot reviewed 13 out of 14 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
diskann-pipnn/src/lib.rs	Adds public PiPNN API (PiPNNConfig, PiPNNBuildContext, build_graph) and stage orchestration.
diskann-pipnn/src/partitioning.rs	Implements deterministic overlapping partition construction and leader assignment/scatter.
diskann-pipnn/src/partitioning/tests.rs	Adds unit tests covering partition determinism, invariants, error cases, and helpers.
diskann-pipnn/src/leaf_build.rs	Builds leaf-local symmetric k-NN candidates and accumulates global candidates safely in parallel.
diskann-pipnn/src/leaf_build/tests.rs	Adds unit tests for candidate correctness, invariants, type support, and error handling.
diskann-pipnn/src/finalization.rs	Orders/prunes candidate rows using shared robust_prune and validates candidate IDs/shape.
diskann-pipnn/src/finalization/tests.rs	Adds unit tests for pruning behavior and candidate validation failures.
diskann-pipnn/src/tests.rs	Tests effective_metric behavior for integer cosine-normalized handling.
diskann-pipnn/tests/config.rs	Integration tests for config validation and graph-policy compatibility checks.
diskann-pipnn/tests/build_graph.rs	Integration tests for end-to-end graph building, invariants, determinism, and type/metric support.
diskann-pipnn/benches/core.rs	Adds a Criterion benchmark for stage-focused core build scenarios.
diskann-pipnn/Cargo.toml	Updates crate dependencies/dev-dependencies and registers the new core benchmark target.
Cargo.lock	Records dependency graph changes for the updated diskann-pipnn crate dependencies.
.cargo/mutants.toml	Adds mutation-test exclusions for key PiPNN public boundary checks and partitioning invariants.

Comments suppressed due to low confidence (1)

diskann-pipnn/src/partitioning.rs:604

• size_of::<f32>() is used without being in scope (no use std::mem::size_of; and not qualified), so this function won’t compile as written.

fn assignment_stripe_rows(leaders: usize) -> usize {
    (ASSIGNMENT_CACHE_TARGET_BYTES / (leaders.max(1) * size_of::<f32>()))
        .clamp(MIN_ASSIGNMENT_STRIPE_ROWS, MAX_ASSIGNMENT_STRIPE_ROWS)
}

---

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[Copilot]

Pull request overview

Copilot reviewed 13 out of 14 changed files in this pull request and generated 1 comment.

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[Copilot]

Pull request overview

Copilot reviewed 14 out of 15 changed files in this pull request and generated no new comments.

Comments suppressed due to low confidence (2)

diskann-pipnn/src/partitioning.rs:637

• size_of is used without being in scope (std::mem::size_of), which will not compile. Qualify the call or import it.

fn assignment_stripe_rows(leaders: usize) -> usize {
    (ASSIGNMENT_CACHE_TARGET_BYTES / (leaders.max(1) * size_of::<f32>()))
        .clamp(MIN_ASSIGNMENT_STRIPE_ROWS, MAX_ASSIGNMENT_STRIPE_ROWS)
}

diskann-pipnn/src/partitioning.rs:19

• Norm is imported but never used in this module, which will trip unused_imports warnings (and can become CI failures under -D warnings). Remove it from the import list.

use diskann::{utils::VectorRepr, ANNError, ANNResult};
use diskann_linalg::Transpose;
use diskann_utils::views::MatrixView;
use diskann_vector::{distance::Metric, norm::FastL2NormSquared, Norm};
use rand::{prelude::IndexedRandom, SeedableRng};
use rayon::prelude::*;