feat: add anchor-drift-monitor skill - real-time intent drift detection for Oz runs

[HasRahm]

What

Adds a new anchor-drift-monitor skill that detects and prevents cumulative intent drift during multi-step Oz agent runs.

Why

Oz agents can experience cumulative intent drift across multi-step tasks. An agent starts with a clear instruction - "refactor the auth module" - and by step 6 it is modifying unrelated files, changing environment variables, or introducing dependencies outside the original scope. This happens because multi-step context causes gradual faithfulness erosion.

How It Works

1. At the start of a run, the skill creates an intent contract capturing the task + constraints
2. 2. After each step, it scores the action against the contract using HHEM-2.1-Open
3. 3. When faithfulness drops below threshold, it pauses the run and reports what drifted

Benchmark Results

Validated on CNN/DailyMail corpus using Gemma 4 31B + HHEM-2.1-Open:

Metric	Baseline	+ Anchor	Delta
High-fidelity grounding (HHEM >= 0.95)	47.1%	56.3%	+9.2%
Mean HHEM faithfulness score	0.9257	0.9307	+0.005
Hallucination rate (<0.50)	0.8%	0.7%	-0.1%

3:1 improvement ratio - interventions are grounded, not random.
0% regression on IFEval (instruction following) and Tau2 (task completion).

Setup

Requires ANCHOR_KEY environment variable. Free keys at anchor-app-one.vercel.app.

Links

• SDK: github.com/anchor-engine/anchor-sdk
• • npm: npm install @anchor-engine/sdk