[ADR-030] Retrieval Checkpoints and Proof References

[ohdearquant]

Summary

Restore checkpoint store support and reconcile proof/reference comments so retrieval and HNSW persistence no longer point to missing artifacts.

Source ADRs

• F167 ADR-030 (CRIT): HnswCheckpoint and HnswCheckpointStore are commented out because khive_fold::Checkpoint is missing (from audit-platform/e5/ADR-030.md)
• F170 ADR-030 (MAJ): Source comments reference proofs/Lion/Retrieval/Distance.lean, but find proofs -maxdepth 3 -type f returned no proofs/ directory in the repo root. (from audit-platform/e5/ADR-030.md)

Files affected

• crates/khive-retrieval/src/lib.rs (190 sampled LOC)
• crates/khive-hnsw/src/distance.rs (368 sampled LOC)
• crates/khive-hnsw/src/checkpoint/mod.rs (423 sampled LOC)
• proofs/README.md (new/planned path)
• crates/khive-hnsw/src/lib.rs (133 sampled LOC)

Acceptance criteria

• All source findings listed above are addressed exactly once in this cluster.
• Public types, handlers, schema, and docs touched by the affected files agree on the ADR contract.
• Regression tests cover happy path and edge cases for the changed public APIs or schema behavior.
• cargo test -p khive-retrieval -p khive-hnsw passes.
• cargo clippy --workspace -- -D warnings passes.
• make ci passes.

Dependencies

• Depends on: #[ADR-006] Deterministic Score and Fold Primitives
• Depends on: #[ADR-011] Retrieval, Embed, and Lattice Boundary
• Blocks: none

LOC estimate

~140 lines added/30 removed; 4 existing affected file(s) sampled at 1114 current LOC via wc -l, plus 1 new/planned path(s).

Risk notes

• Same-file dependencies must merge first; dependency list includes the exact overlapping paths.
• 1 affected path(s) are new/planned and were not present in rg --files --hidden; create them in the owning PR rather than in independent parallel work.
• Contains CRIT findings; do not defer without owner approval.

Auto-generated by ADR alignment triage

[ohdearquant]

Landed in main via PR #349 (integration of cluster c17 — original cluster PR was #353). Tracker complete.