ADR-350: Trust-Weighted Consensus for Swarm Coordination

Field	Value
Status	Proposed
Authors	claude (dream-cycle agent, 2026-06-24)
Date	2026-06-24
Dream Cycle Surface	swarm (DEEP)
Supersedes	none
Related	ADR-162 (prior swarm ADR, 2026-06-19)

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Context

The 2026-06-24 dream-cycle session surveyed swarm SOTA for 2026. Two peer-reviewed papers are directly actionable:

1. SGTO-MAS (arXiv:2606.07940) demonstrates that adding a Bayesian trust score to consensus voting reduces degradation under adversarial agent removal from unbounded to only 2.5 % and under consensus disruption to 5.3 %, while maintaining a consensus level of 0.8764. The mechanism: each agent maintains a trust_score ∈ [0,1] updated via exponential smoothing (trust_new = trust_old * 0.9 + outcome * 0.1). Votes are weighted by trust score before the majority/quorum threshold is applied.

2. RAPS (arXiv:2602.08009) extends this with Bayesian reputation detection for malicious peers in publish-subscribe topologies, tested across 5 benchmarks.

Ruflo's current consensus stack (raft, byzantine, gossip, CRDT, quorum) has no trust or reputation layer. A compromised or misbehaving agent has equal voting weight to a healthy one. This is a security and reliability gap.

Decision

Add an optional trust-weighted mode to Ruflo's consensus mechanisms, starting with raft and byzantine:

1. Agent heartbeat extension: Add trust_score: number (0–1, default 1.0) to the per-agent state tracked by hierarchical-coordinator and raft-manager.

2. Vote weighting: Before applying quorum threshold, multiply each vote by the sender's trust_score. Effective majority = sum(trust_i * vote_i) / sum(trust_i) >= 0.5.

3. Trust update on outcome: After each task cycle, update trust via trust_i = 0.9 * trust_i + 0.1 * outcome_i where outcome_i ∈ {0, 1} based on whether agent i's output passed validation.

4. Configuration flag: trustWeightedConsensus: boolean (default false) in swarm init options. Existing behaviour unchanged when disabled.

5. Malicious agent eviction threshold: When trust_i < 0.2 for three consecutive cycles, the agent is marked degraded and removed from the quorum pool by the queen coordinator.

Consequences

Positive:

• Matches SGTO-MAS Grade A benchmark: ≤5.3 % degradation under adversarial conditions
• Zero new external dependencies (pure arithmetic, no library required)
• Backwards-compatible via feature flag
• Enables detection of systematically failing agents (network partition, zombie processes)

Negative:

• Adds state to agent heartbeats (~8 bytes per agent per cycle)
• Cold-start problem: all agents start at trust 1.0; rogue agents take ≥10 cycles to degrade below 0.5
• Trust convergence speed (α=0.1) is a tunable guess — requires empirical validation

Implementation Notes

• Touch files: v3/@claude-flow/cli/src/swarm/raft-manager.ts, hierarchical-coordinator.ts, swarm-init.ts
• Estimated effort: 2 engineering days
• Test: inject a 25 % fault rate into one agent in a 4-agent raft quorum; assert consensus remains ≥0.75 after 20 cycles
• Do NOT change the default trustWeightedConsensus: false; this is opt-in only

Alternatives Considered

• Static reputation list (block known-bad agent IDs at config time): rejected — doesn't adapt at runtime.
• Full Byzantine BFT only (already available as byzantine topology): rejected as overkill for non-adversarial deployments; trust weighting is lighter and composable with any topology.
• No action (wait for more data): rejected — Grade A paper with numeric benchmarks justifies implementation.

References

• arXiv:2606.07940 — SGTO-MAS (Secure Gorilla Troops Optimization for Multi-Agent Systems)
• arXiv:2602.08009 — RAPS (Reputation-Aware Publish-Subscribe)
• Dream Cycle research file: v3/docs/research/dream-2026-06-24-swarm.md
• Prior swarm ADR: ADR-162 (2026-06-19)