M1: OSS policy engine, golden fixtures, SPEC v0.5 implementation spec

.github/workflows/lexshield-check.example.yml

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+# Example workflow: validate policy packs in CI.
+# Copy to .github/workflows/lexshield-check.yml once the CLI is published.
+
+name: LexShield Policy Check
+
+on:
+  push:
+    branches: [main]
+    paths:
+      - "packs/**"
+      - "schemas/**"
+      - "lexshield.yaml"
+      - "policy.yaml"
+      - "rules.yaml"
+  pull_request:
+    paths:
+      - "packs/**"
+      - "schemas/**"
+      - "lexshield.yaml"
+      - "policy.yaml"
+      - "rules.yaml"
+
+jobs:
+  lexshield-check:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Set up Python
+        uses: actions/setup-python@v5
+        with:
+          python-version: "3.11"
+
+      - name: Install LexShield CLI
+        run: pip install lexshield
+
+      - name: Validate shipped policy packs
+        run: |
+          for pack in baseline-deny pii-guard change-window; do
+            echo "Checking pack: $pack"
+            lexshield check \
+              --policy "packs/${pack}/policy.yaml" \
+              --rules "packs/${pack}/rules.yaml" \
+              --strict
+          done
+
+      - name: Validate root policy (if present)
+        if: hashFiles('lexshield.yaml') != ''
+        run: lexshield check --strict

.gitignore

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+# LexShield local state
+.lexshield/
+traces.ndjson
+
+# Accidental init at repo root during development
+/lexshield.yaml
+/policy.yaml
+/rules.yaml
+
+# Python
+__pycache__/
+*.py[cod]
+*$py.class
+*.so
+.Python
+.venv/
+venv/
+ENV/
+env/
+*.egg-info/
+.eggs/
+dist/
+build/
+*.egg
+.pytest_cache/
+.mypy_cache/
+.ruff_cache/
+.coverage
+htmlcov/
+.tox/
+.nox/
+pip-wheel-metadata/
+*.manifest
+*.spec
+
+# uv
+.uv/
+uv.lock
+
+# Node / pnpm
+node_modules/
+.pnpm-store/
+npm-debug.log*
+yarn-debug.log*
+yarn-error.log*
+pnpm-debug.log*
+*.tsbuildinfo
+
+# Build outputs
+dist/
+out/
+lib/
+coverage/
+
+# IDE / OS
+.idea/
+.vscode/
+*.swp
+*.swo
+*~
+.DS_Store
+Thumbs.db
+
+# Environment
+.env
+.env.*
+!.env.example
+
+# Test / tooling artifacts
+.hypothesis/
+.pytest_cache/
+vitest.config.ts.timestamp-*

.python-version

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+3.11

LICENSE

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+MIT License
+
+Copyright (c) 2026 LatticeAG
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.

NOTICE

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+LexShield
+Copyright (c) 2026 LatticeAG
+
+This product includes software developed by LatticeAG (https://latticeag.com).
+
+LexShield is distributed under the MIT License. See LICENSE for the full text.

README.md

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+# LexShield
+
+**The open-source policy firewall for agent tool calls.**
+
+LexShield sits between an AI agent and its tool fleet, classifies the intent behind each tool call, and enforces allow/block/challenge policy **before** execution. Fully local-first — no SaaS required.
+
+- **License**: MIT
+- **Publisher**: [LatticeAG](https://latticeag.com)
+- **Specification**: see [SPEC.md](./SPEC.md) for product scope, APIs, and v0.1 feature freeze
+
+## Quickstart (5 minutes, deterministic-only)
+
+No API key required for the deterministic path.
+
+```bash
+# Install (PyPI — coming soon)
+pip install lexshield
+
+# Scaffold config + baseline policy pack
+lexshield init --pack baseline-deny
+
+# Validate policy
+lexshield check
+
+# Evaluate a tool call offline
+lexshield evaluate --tool send_email --args '{"to":"user@example.com","body":"AKIA0123456789012345"}' --json
+# → BLOCK (security.secret_exposure)
+
+# Allow a health check
+lexshield evaluate --tool health_check --args '{}' --json
+# → ALLOW
+```
+
+### Path outline
+
+1. **Install** — `pip install lexshield` (Python SDK + CLI)
+2. **Init** — `lexshield init` writes `lexshield.yaml`, `policy.yaml`, `rules.yaml`
+3. **Check** — `lexshield check` validates policy in CI (exit non-zero on errors)
+4. **Evaluate** — `lexshield evaluate` or `Shield.guard` decorator before tool execution
+5. **Trace** — verdicts append to `traces.ndjson` for audit
+
+For TypeScript: `npm install @latticeag/lexshield` (evaluate + guard parity).
+
+## Monorepo layout
+
+| Package | Path | Role |
+|---------|------|------|
+| Python engine | `packages/engine-py` | Policy engine, classifiers (source of truth) |
+| Python CLI | `packages/cli` | `lexshield` Typer CLI |
+| TypeScript SDK | `packages/engine-ts` | `@latticeag/lexshield` evaluate/guard |
+
+## Development
+
+```bash
+# Python (uv workspace)
+uv sync
+uv run pytest
+
+# TypeScript (pnpm workspace)
+pnpm install
+pnpm -r test
+```
+
+See [SPEC.md](./SPEC.md) for architecture, policy language, intent taxonomy, and acceptance criteria.