research(nightly): tiered-agent-memory — coherence-driven hot/warm/cold tier promotion

[ruvnet]

Adds nightly RuVector research for tiered-agent-memory.

Summary

• Topic: Tiered Agent Memory with Coherence-Driven Hot/Warm/Cold Tier Promotion
• Scored 4.45/5.0 via 3-pass SOTA loop; validated by MEMTIER arXiv:2605.03675 (May 2026)
• First Rust implementation of coherence-gated tier promotion for agent vector memory
• Three variants: FlatMemory (baseline), LruTieredMemory (alt-A), CoherenceTieredMemory (alt-B)

Deliverables

1. Working Rust PoC: crates/ruvector-tiered-memory — 11 unit tests, all passing
2. ADR: docs/adr/ADR-194-tiered-agent-memory.md
3. Research document: docs/research/nightly/2026-05-19-tiered-agent-memory/README.md
4. Public gist: docs/research/nightly/2026-05-19-tiered-agent-memory/gist.md
5. Real benchmark results (x86-64 Linux 6.18.5, rustc 1.87.0)

Benchmark Results

Variant	mean µs	p50 µs	p95 µs	QPS	memory KB	recall@10
FlatMemory (baseline)	884.9	880.9	934.9	1,119	2,500	100.0%
LruTieredMemory (alt-A)	1,067.5	1,049.3	1,189.2	926	1,888	80.5%
CoherenceTieredMemory (alt-B)	956.6	930.9	1,104.0	1,044	2,408	100.0%

Acceptance result: PASS — all variants recall@10 ≥ 75%

Key Finding

CoherenceTieredMemory achieves 100% recall at 4% memory reduction by keeping the warm tier small (250/5000 vectors). The coherence signal (cosine similarity to running query centroid) concentrates full-precision search on semantically relevant memories. LruTieredMemory saves 24% memory at 80.5% recall — an honest tradeoff for approximate workloads.

Ecosystem Connections

• prime-radiant — coherence scoring engine (centroid-based cosine similarity)
• ruvector-diskann — natural cold-tier backend for Phase 2
• ruvector-verified — proof-gated warm→cold eviction (Phase 3)
• mcp-gate — MCP tool surface for agent memory (Phase 3)
• ruvector-raft — distributed centroid consensus (Phase 3)
• ruFlo — scheduled nightly rebalancing (Phase 3)

Build

git checkout research/nightly/2026-05-19-tiered-agent-memory
cargo build --release -p ruvector-tiered-memory
cargo test -p ruvector-tiered-memory
cargo run --release -p ruvector-tiered-memory

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