[umpireboulianne-design]

Summary

Exposes first-class solvency and coverage-ratio health views on RefractBackstop alongside a permissionless check_health evaluator that emits threshold crossing and recovery events with configurable hysteresis.

Closes #239

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Changes

• Pool Coverage View (pool/src/lib.rs):
  • Added aggregate_in_force_coverage(env) as a cheap single-read view returning the pool's active in-force coverage from PoolAccounting.
• Backstop Solvency & Coverage-Ratio Health Views (backstop/src/lib.rs):
  • total_staked_capital(env): pure read-only view returning total staked capital across tranches.
  • aggregate_in_force_coverage(env): pulls live coverage from RefractPool::aggregate_in_force_coverage via try_invoke_contract and degrades gracefully to the cached coverage counter (DataKey::CachedCoverage) when the pool read is unavailable.
  • encumbered_capital(env) and idle_capital(env): pure read-only views for capital encumbered by in-force coverage vs. unencumbered capital.
  • solvency_ratio_bps(env), coverage_ratio_bps(env), and feed_utilization_bps(env, feed): pure read-only views computed via the 1e7 fixed-point helper (FP_SCALE), returning Ok(None) (never panicking) when the denominator is zero.
  • health_snapshot(env): consolidated read-only view returning BackstopHealthSnapshot.
• Threshold Alert Events with Hysteresis (backstop/src/lib.rs):
  • set_health_thresholds(env, caller, min_solvency_bps, max_coverage_bps, hysteresis_bps): admin-gated configuration for alert thresholds and recovery hysteresis band.
  • check_health(env): permissionless evaluator that checks solvency and coverage ratios against configured thresholds and emits HLTHALRT / HLTHRECV events only on state transitions across the threshold / hysteresis band.
• Unit Tests (backstop/src/test.rs):
  • Zero-coverage and zero-capital edge cases returning None without panicking
  • 100% utilization and >100% under-collateralized edge cases
  • Precision/overflow tests at i128 upper bounds (1e30)
  • Threshold alert emission on breach, suppression on repeated checks, hysteresis band holding, and recovery emission once ratios cross back beyond the hysteresis band

Checklist

• Zero unwrap(), expect(), or panic!() calls in non-test contract code
• Pure read-only health views with no state mutation
• Unit tests covering edge cases, overflow bounds, and hysteresis event transitions