[PeerX Backlog # 93] Prometheus exporter for cache hit ratio

[ameeribro4-sudo]

Problem Statement
get_cache_stats(env) -> (hits, misses, ratio_bps) is on chain but
not exposed in a way off-chain Prometheus can scrape.

Expected Outcome
A Rust binary peerx-metrics-exporter that polls get_cache_stats
and exposes /metrics HTTP endpoint.

Acceptance Criteria

• Runs as systemd unit (documented in docs/OPERATIONS.md).
• Sample dashboard JSON in dashboards/cache.json for Grafana.

Files Affected

• bin/peerx-metrics-exporter/ (new),
  dashboards/cache.json (new).

Difficulty / Effort 🥑 / M
Labels observability, ops

[GBOYEE]

Hi team — I'd like to take this on as part of the GrantFox campaign. I'll implement it and open a PR referencing this issue shortly.

[Primex-hub]

I would love to solve this issue

[Gracora]

please assign me this issue please, I have experience.

[grantfox-oss]

🦊 GrantFox — @Gracora has been assigned to this issue as part of the Official Campaign | FWC26 campaign!

Next steps:

1. Open a Pull Request referencing this issue (e.g., Closes #93)
2. Your PR will be reviewed by the OpenPeerX maintainers

Good luck! Track your progress on GrantFox.

[grantfox-oss]

🎉 This issue has been marked as completed on GrantFox as part of the Official Campaign | FWC26 campaign!

@Gracora's PR #117 was approved and merged by @ameeribro4-sudo.

🏆 @Gracora: You earned 35 FoxPoints for this contribution! Your current tier: Explorer (83 total points). Track your full progress on GrantFox.

👏 Great work, @Gracora! Keep contributing to OpenPeerX.