jev-harness (Rust)

Zero-overhead System One decision harness & token optimizer for AI coding agents and Tauri applications.

jev-harness wraps TypeSafe Jev System One micro-decisions with local fast heuristics (< 500µs) and remote sub-second inference (70-300ms). It prevents catastrophic token waste ($10-$50/M frontier reasoning calls) by detecting dependency errors, circular failure loops, and deterministic routing locally.

⚡ Key Capabilities

Test & Process Failure Triage (triage_test_failure):
- Detects missing modules (TS2307, Cannot find module, ModuleNotFoundError, E0463), flaky network timeouts (ETIMEDOUT, ECONNRESET), and syntax errors in < 500µs locally.
- Tells your agent or process runner to install dependencies or retry without invoking expensive frontier LLMs (skip_llm: true).
Loop & Doom Prevention (should_abort_trajectory):
- Evaluates consecutive identical test failures and repetition loops to kill runaway agentic runs before burning budget.
Dynamic Model Routing (route_model_tier):
- Routes simple tasks, typos, and lint errors to fast deterministic models, and reserves expensive 2026 reasoning models (GPT-6 Astra, Claude Fable 5.1 / Mythos 5.1) only for complex architectural asks.
Step Completion Verification (verify_step_completion):
- Confirms criteria satisfaction before concluding multi-step workflows.

📦 Installation

Add to your Cargo.toml:

[dependencies]
jev-harness = "0.1"
tokio = { version = "1", features = ["full"] }

Or install the standalone CLI:

cargo install jev-harness

🚀 Usage

1. Test Failure Triage

use jev_harness::gates::triage_test_failure;

#[tokio::main]
async fn main() {
    let error_log = "error[E0463]: can't find crate for 'serde'";
    let decision = triage_test_failure(error_log, None).await.unwrap();

    if decision.skip_llm {
        println!("[ACTION] {}", decision.action_recommendation);
    } else {
        println!("[FORWARD] Deep bug detected. Route to frontier LLM.");
    }
}

2. Trajectory Loop Abort Guard

use jev_harness::gates::should_abort_trajectory;

#[tokio::main]
async fn main() {
    let history = "Attempt 1 failed with connection timeout\nAttempt 2 failed with connection timeout";
    let step = "Repeat identical prompt with no code changes";

    let check = should_abort_trajectory(step, history, None).await.unwrap();
    if check.should_abort {
        eprintln!("[KILL AGENT] {}", check.reasoning_summary);
    }
}

3. Model Tier Routing

use jev_harness::gates::route_model_tier;

#[tokio::main]
async fn main() {
    let routing = route_model_tier("Refactor auth system architecture", None).await.unwrap();
    println!("Selected Tier: {}", routing.selected_tier);
    println!("Recommended Model: {}", routing.recommended_model);
}

4. CLI Usage

# Run triage on a traceback
jev triage "Cannot find module 'lodash'"

# Trajectory abort check
jev abort-check --plan "Try identical prompt again"

# Route model tier
jev route --task "Fix typo in variable name"

# Check system status
jev status

jev-harness 0.1.0