## Problem
16 of the 24 pairwise indicators (`type Input = (f64, f64)`) accepted non-finite input unchecked. A single NaN/Inf tick produced a NaN reading, contradicting the streaming-robustness guarantee that *a single bad tick cannot silently poison state* (README, `ARCHITECTURE.md`).
The other 8 pairwise indicators (`Alpha`, `InformationRatio`, `KalmanHedgeRatio`, `PairSpreadZScore`, `PairwiseBeta`, `RelativeStrengthAb`, `SpreadBollingerBands`, `TreynorRatio`) already guard finite input and are untouched. Scalar (169 files) and candle (`Candle::new`) inputs were already protected.
## Severity split
- **7 running-sum indicators** \(permanent corruption — NaN entered `Σ` and stayed until `reset()`\): `Beta`, `BetaNeutralSpread`, `Cointegration`, `HasbrouckInformationShare`, `PearsonCorrelation`, `RollingCorrelation`, `RollingCovariance`.
- **9 buffer-recompute indicators** \(transient — NaN cleared once evicted, but still surfaced in the reading\): `DistanceSsd`, `GrangerCausality`, `KendallTau`, `LeadLagCrossCorrelation`, `OuHalfLife`, `SpearmanCorrelation`, `SpreadAr1Coefficient`, `SpreadHurst`, `VarianceRatio`.
## Fix
Add the established finite-input guard (the same pattern `Alpha` already uses) as the first step of `update()`, before any window or sum mutation. Signature unchanged → bindings re-export unchanged, no binding regen needed; core-only.
Each indicator gains a `non_finite_input_returns_none` test that exercises the guard (NaN and Inf, covering both `||` operands) and proves a clean warmup is unaffected by the rejected ticks.
Split into two commits by severity class.
## Verification
- `cargo fmt --all` clean
- `cargo test --workspace --all-features` — 4225 core tests pass (+16 new)
- `cargo clippy --workspace --all-targets --all-features -- -D warnings` clean
kingchenc
99497eb062