wsr

sandbox

Wasm-based execution sandbox. Every step runs in its own isolated Wasmtime instance with explicit capability grants.

design

• One Store + Instance per step, dropped immediately after completion
• Cranelift JIT compilation with optional AOT cache
• WASI 3 — native async layer to Wasm
• No Docker. No daemon.

capability model

Steps get exactly the capabilities they need and nothing more. Capabilities are granted at step instantiation time:

capability	mechanism
Filesystem access	WASI preopened directories
Environment variables	explicit env grants
Network access	allowed_hosts enforced via hyper proxy
Secrets	injected as env vars, zeroized on drop, never written to disk

A step that reaches a host outside allowed_hosts gets an immediate local error:

capability denied: net → registry.example.com
hint: add to sandbox.allowed_hosts in wsr.json

aot module cache

Compiled Wasm modules are cached using wasmtime::Module::serialize and pinned with a SHA-256 hash of the source. Subsequent runs skip recompilation.

source

• src/sandbox/mod.rs

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