Installation
Add @sigx/runtime-core to your project.
Install the package
pnpm add @sigx/runtime-core @sigx/reactivity@sigx/runtime-core peers on @sigx/reactivity (^1.0.0), so install both — or install sigx, which brings both in. A library declares them under peerDependencies rather than dependencies, so it resolves to the app's copy; see the install shape.
One copy per page
The current-instance slot, the app contexts and the DI tokens live in this package, so a realm must hold exactly one copy of it — the same singleton rule as @sigx/reactivity. A second copy evaluating in the same realm throws in development ([sigx] Two copies of @sigx/runtime-core are loaded: <version> at <url> and <version> at <url>.) and warns once in production. The cause is always an install with two resolutions — two versions in the lockfile, or a library that bundled its own copy — and the fix is the same: the app installs sigx once, libraries peer on it. See Stability & versioning.
Verify
import * as RuntimeCore from '@sigx/runtime-core';
console.log(Object.keys(RuntimeCore));