> ## Documentation Index
> Fetch the complete documentation index at: https://docs.hexgate.ai/llms.txt
> Use this file to discover all available pages before exploring further.

# WASM bundles

> Compile policy.yaml to a portable signed artifact.

Hexgate has **two policy enforcement engines** that return identical decisions
(a parity test suite proves it):

* **pydantic** (default) — evaluates constraints in-process. Zero setup; this is
  what every example uses.
* **WASM** — compiles `policy.yaml` → Rego → a WebAssembly module evaluated via
  `wasmtime`. This is the path production ships: one compiled artifact,
  byte-for-byte reproducible, cryptographically [signed](/policy/signing) by the
  platform.

Why a second engine: the WASM path produces a **portable, signed artifact** (a
"bundle"), surfaces **structured deny reasons** (exactly which constraints
failed), and chains trust back to the platform's signing key — the same key that
signs your biscuit tokens. See [internals/rego-wasm](/internals/rego-wasm) for the
engineering snapshot.

## Building a bundle

The compile step needs the `opa` binary — see the
[`hexgate policy` CLI](/cli/policy#prerequisite-opa).

```bash theme={null}
hexgate policy build policy.yaml --out ./bundle
```

`hexgate policy build` produces a directory:

| File                     | Contents                                                           |
| ------------------------ | ------------------------------------------------------------------ |
| `{stem}.yaml`            | the source policy (verbatim)                                       |
| `{stem}.rego`            | the compiled Rego module                                           |
| `{stem}.wasm`            | the WebAssembly module — what actually evaluates at runtime        |
| `{stem}.bundle.json`     | manifest: sha256 of each artifact + a `wasm_hash`                  |
| `{stem}.bundle.json.sig` | detached Ed25519 signature over the manifest (signed bundles only) |

The manifest's hashes authenticate the files; the signature authenticates the
manifest. Verifying both proves the whole bundle came from the trusted signer,
untampered.

## Enforcing a bundle locally

Point an agent at a local source and every tool call routes through the WASM
engine instead of pydantic — no platform needed. Both YAML and bundle-dir sources
hot-reload on save. See [local override](/policy/local-override) for the two
shapes and the shared refresh seam, and [signing](/policy/signing) for the
signature-verification matrix.