ADR-356: Cross-Agent KV-Cache Sharing for Swarm Performance

Status: Proposed Date: 2026-06-30 Authors: claude (dream-cycle agent, 2026-06-30) Dream Cycle: SLOT=0, DEEP=performance, source issue TBD Related ADRs: ADR-006 (Unified Memory Service), ADR-009 (Hybrid Memory Backend), ADR-163 (Multi-Agent Benchmarking Suite)

Context

As of June 2026, Ruflo spawns each agent in a swarm with an independent inference context. When 8 agents share the same system prompt (the default in CLAUDE.md's maxAgents=8 anti-drift config), each agent sends the full system-prompt prefix to the model on every turn. At ~8k tokens per system prompt and 8 agents, this is 64k tokens of redundant prefill per swarm turn.

TokenDance (arXiv 2604.03143, April 2026, Grade A) is the first published paper to quantify collective KV-cache sharing across concurrent LLM agents:

The paper pools KV-cache entries by prefix hash across agents sharing a common context (system prompt, conversation history prefix), eliminating redundant computation. The approach is model-agnostic and does not require model weight changes.

No competitor framework has productized this pattern. LangGraph, AutoGen, CrewAI, and OpenAI Swarm all use per-agent independent contexts as of June 2026.

Additionally, TraceLab (arXiv Jun 2026, Grade A) characterizes 4,300 real coding-agent sessions and identifies context bloat (extensive input contexts with concise outputs) as the dominant latency driver — precisely the scenario that prefix-cache sharing addresses.

Ruflo already maintains a hybrid memory backend (SQLite + AgentDB) and a SharedKVCache concept exists at the infrastructure level (the storeEntry/searchEntries API). The missing piece is a prefix-hash pool that maps (session_id, prompt_hash) → cached_kv_block_id and is consulted before each agent turn.

Decision

Add a SharedKVCacheNamespace class to @claude-flow/memory that implements prefix-hash pooling for swarm agents. The feature is opt-in via environment variable to avoid breaking existing behavior.

Interface

// @claude-flow/memory/src/shared-kv-cache.ts

export interface KVCacheEntry {
  prefixHash: string;          // sha256 of (session_id + prompt_prefix)
  cachedTokenCount: number;
  hitCount: number;
  createdAt: number;
  lastHitAt: number;
}

export class SharedKVCacheNamespace {
  constructor(private sessionId: string, private agentDb: AgentDB) {}

  /** Check if prefix is already cached; return entry or null */
  async lookup(promptPrefix: string): Promise<KVCacheEntry | null>;

  /** Register a new cache entry after first computation */
  async register(promptPrefix: string, tokenCount: number): Promise<KVCacheEntry>;

  /** Record a cache hit */
  async hit(prefixHash: string): Promise<void>;

  /** Evict entries older than maxAgeMs or with hitCount < minHits */
  async evict(opts: { maxAgeMs?: number; minHits?: number }): Promise<number>;

  /** Return cache stats for the current session */
  async stats(): Promise<{ entries: number; totalHits: number; estimatedTokensSaved: number }>;
}

Activation

# Enable (off by default)
CLAUDE_FLOW_KV_SHARE=true npx claude-flow swarm init --topology hierarchical

# Or via config
{
  "performance": {
    "kvCacheSharing": true,
    "kvCacheMaxAgeMs": 3600000,
    "kvCacheMinHits": 2
  }
}

Integration Points

1. swarm init — when CLAUDE_FLOW_KV_SHARE=true, create a SharedKVCacheNamespace instance keyed to the swarm session ID
2. agent spawn — pass the shared namespace to each agent's context; agents consult before sending prefix tokens
3. post-task hook — evict stale entries after task completion
4. performance benchmark --suite kvcache — new benchmark mode to measure actual hit rates and token savings

Consequences

Positive

• Targets 17.5× per-agent cache reduction at 8-agent swarm scale (Grade A evidence from TokenDance)
• 1.9× prefill speedup expected for common-system-prompt workloads
• No model weight changes required; works with any provider
• CLAUDE_FLOW_KV_SHARE=false default preserves all existing behavior

Negative / Risks

• Cache invalidation complexity: stale entries must be evicted when system prompt changes
• Cross-agent security boundary: shared cache entries must not leak agent-private state (mitigated by keying only on the shared prefix, not per-agent turn history)
• Memory overhead: the KV-cache namespace adds entries to AgentDB; must set TTL and size limits
• The TokenDance results are for a specific model and GPU configuration; actual speedup on Ruflo's provider calls (API, not GPU) may be lower (C — implementation-dependent)

Neutral

• ADR-163's benchmarking suite must be extended (see Recommended Actions in gist) before any public claims are made about this speedup

Implementation Plan

Phase 4 must precede any public speedup claims.

References

• TokenDance: arXiv 2604.03143 (Apr 2026) — collective KV-cache sharing
• TraceLab: arXiv Jun 2026 — context bloat as dominant latency driver
• UltraQuant: arXiv 2606.20474 (Jun 2026) — 4-bit KV caching (complementary, not prerequisite)
• ADR-163: multi-agent benchmarking suite — must be extended before publishing results
• ADR-006: Unified Memory Service — AgentDB backend used for cache namespace storage