test: evals harness

[amal66]

Summary

Adds evals/, a zero-dependency, fully offline, deterministic legal-AI evaluation harness: a curated golden dataset (8 synthetic cases), five deterministic scorers (citation accuracy, keyword recall, field extraction, prompt-injection resistance, privilege/PII leakage), and a fixture-based mock runner that produces a scorecard and a CI-gating exit code with no network, no LLM calls, and no secrets.

Changes

• evals/run.mjs — CLI entry point (--threshold, --break, --json, --dataset); exits non-zero when pass rate < threshold
• evals/src/engine.mjs — dataset loading + run loop + aggregate stats
• evals/src/scorers.mjs — the five deterministic scorers
• evals/src/runners/fixture-runner.mjs — offline mock runner replaying committed fixtures, with a deliberate-failure mode
• evals/datasets/golden.json + golden.schema.json — 8 synthetic cases (no real/copyrighted document text) + JSON Schema
• evals/fixtures/model_outputs.json — recorded mock outputs
• evals/package.json — private, zero-dependency (npm test → node run.mjs)
• evals/README.md — usage, scorer semantics, an honest "what this does NOT cover" scope section, and a sketch for plugging in a live provider

The harness is entirely self-contained (relative imports only, no dependencies), so it runs unchanged on this layout: node evals/run.mjs from the repo root. Nothing was left behind — no part of the fork's harness depends on fork-only modules.

Why

Mis-citation, prompt injection via document content, and privilege/PII leakage are the highest-stakes failure modes for a legal-AI assistant, and all three are cheap to regression-test deterministically. This gives the repo a runnable scorecard that can gate CI (see the companion CI workflow PR, whose evals job runs node evals/run.mjs --threshold 1.0 once this merges).

Testing

• node evals/run.mjs — 8/8 cases pass, mean score 0.979, exit code 0
• node evals/run.mjs --break privilege-pii-ssn — one case flips to FAIL, exit code 1 (verifies the CI gate actually fails)
• node --check on all four .mjs sources — clean
• Backend unaffected but re-verified on this branch: npm ci && npm run build (tsc) in backend/ — green

Provenance

All lines are mechanical ports of amal66/mike@origin/main (commit b3166dd); exceptions: none — evals/ is a byte-for-byte verbatim copy (verified with diff against origin/main:evals/*); the harness is self-contained, so no path/import adaptation was needed. The private package name @mike/evals in evals/package.json is kept verbatim; the package is never published or depended on.

🤖 Generated with Claude Code

https://claude.ai/code/session_01CEguyEgXa9JjCciXCcVemC