fix(pegs): per-feed oracle↔market divergence threshold (fix cbBTC false positive)#310
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…se positive) The L2 divergence check used a flat 1% threshold, tighter than some feeds' own on-chain deviation band. A Chainlink feed only re-pushes when price moves past that band, so the oracle legitimately lags the live market by up to the band — cbBTC/USD (2% band) lagging ~1.14% tripped a HIGH alert and the emergency dispatch hook (forced_cap: 0 on coinbase markets). A false positive by design. - Add per-feed ChainlinkFeed.deviation_threshold, verified against Chainlink's reference data directory: USDC/USDT 0.25%, USDS 0.3%, USDe/WBTC-BTC/LBTC-BTC 0.5%, cbBTC 2%. - Divergence now fires at deviation_threshold + buffer. Buffer defaults to 0.25% (tight, for stable/ratio answers) and is per-feed overridable: cbBTC widens to 0.5% since its answer tracks the volatile BTC price and can overshoot the band. - Real depegs remain covered independently by check_peg_deviation. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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Problem
Production fired a false HIGH alert — and it escalated to the emergency
forced_cap: 0dispatch on Coinbase-collateral markets:check_market_divergenceused a flat 1% threshold. But a Chainlink feed only pushes a new answer when the price moves past its on-chain deviation parameter, so the oracle legitimately lags the live market by up to that band. cbBTC/USD's band is 2%, so a ~1.14% lag is normal update behaviour, not an anomaly — the flat 1% was tighter than the feed's own band.Fix
Divergence now triggers at
feed deviation band + buffer, both per-feed.ChainlinkFeed.deviation_threshold— each feed's real band, verified against Chainlink's reference data directory:divergence_buffer— slack for overshoot / cross-source noise. Default 0.25% (tight — right for stable/ratio answers). cbBTC overrides to 0.5%, because it's the one feed whose answer tracks the full volatile BTC price and can overshoot its band on a fast move (WBTC/BTC and LBTC/BTC are ~1.0 ratios, so they keep the tight default).Effective triggers: stables 0.5–0.75%, cbBTC 2.5%. The 1.14% that fired now sits comfortably under cbBTC's 2.5%, while the stables get tighter than the old flat 1% (a real stable depeg trips sooner). Genuine depegs are still caught independently by
check_peg_deviation(oracle vs peg), so loosening divergence creates no blind spot.The
PEG_ORACLE_DIVERGENCE_THRESHOLDenv var is replaced byPEG_ORACLE_DIVERGENCE_BUFFER(global buffer override; per-feed values otherwise).Tests
Regression tests added: the exact ~1.14%-within-band scenario stays quiet; cbBTC's wider 0.5% buffer and USDC's tight 0.25% default are both locked in. Full suite green, ruff clean.
Known follow-ups (not in this PR)
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