Implement node reputation scoring for decentralized RPC node selection

[Smartdevs17]

Context

Soroban contract transactions can be submitted through multiple RPC nodes. No intelligent selection mechanism exists beyond simple round-robin.

Current Limitation/Problem

If a node is slow or returns incorrect data, the entire transaction fails. Users have no visibility into node health.

Expected Outcome

Node reputation scoring: track response time, success rate, data freshness, and liveness per node. Score-based weighted selection with automatic dead node removal.

Acceptance Criteria

• Metrics per node: response time (p50, p95, p99), success rate (24h rolling), last block height, liveness (ping every 30s)
• Reputation score formula: 40% success rate + 30% inverse latency + 20% freshness + 10% liveness
• Node selection: weighted random selection by score (higher score = higher probability)
• Dead node detection: 5 consecutive failures -> mark dead, retry health check every 5 min
• Score persistence: Redis with 5-minute TTL per node score
• Fallback chain: primary (highest score) -> secondary -> tertiary for each transaction
• Edge case: all nodes dead -> circuit breaker opens, alert ops team, retry every 30s
• Edge case: new node starts with neutral score (50th percentile) to allow fair evaluation

Technical Scope

• backend/shared/soroban/ - NodeReputationService
• backend/shared/soroban/ - NodeSelector (weighted random selection)
• backend/monitoring/ - node health and reputation metrics
• backend/config/ - node registry with endpoints and metadata
• backend/shared/cache/ - score persistence in Redis

[Max-Owolabi]

@Max-Owolabi has applied to work on this issue as part of the Stellar Wave Program's 6th wave.

I am a software engineer with knowledge with resolving issues of this nature

ℹ️ Repo Maintainers: To accept this application, review their application or assign @Max-Owolabi to this issue.

[drips-wave]

Congratulations, @Max-Owolabi! 🎉 Your application was accepted by the repo's maintainers, and the issue is due on June 30, 2026.

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