Node-pack runtimes

Status: Stable.

Normative home: nodePackRuntimes.

Why this exists

This is the v2 contract for the language a node pack runs in. It also lets a remote pack name its MCP server by an inline MCP Registry record instead of a bare URL. The shape is $defs/Runtime in schemas/v2/node-pack-manifest.schema.json.

Languages

runtime.language is one of javascript, python, go, wasm, wasm-component, remote. entry is a path inside the tarball, or, for remote, the URL of an MCP server the host calls as an MCP client. A host MAY refuse a language it cannot execute, at workflow registration and with unsupported_runtime.

WASM

• A host that loads wasm packs MUST advertise nodePackRuntimes.wasm with at least one abiVersions[] entry, and MUST reject at load a pack whose openwop_abi_version() is not listed.
• When it advertises maxMemoryBytes it MUST enforce it and emit cap.breached with kind: "wasm-memory" on a breach.
• nodePackRuntimes.wasmComponent advertises wasm-component loading; its interfaces are reserved for a later RFC.

The MCP registry record

A remote runtime MAY carry mcpServer, an inline subset of an MCP Registry server.json (schema 2025-12-11):

• name, description, version;
• optional title, websiteUrl and repository;
• exactly one remotes[] entry of type: "streamable-http" with an https:// URL.

It has no packages[], headers, variables or _meta, so it carries no install instruction and no credential. The record is by value; this contract defines no registry lookup.

• mcpServer under any other language, or an entry that differs from remotes[0].url, makes the manifest invalid (pack_validation_failed).
• A host SHOULD NOT treat name as a verified identity: an inline record carries no proof of namespace ownership.
• A host that authenticates to the server does so through the node's requiredCredentials or auth.

Sources: RFCs 0008, 0203.