Variable SIMULATION_SYSTEMSConst

§81's "animation systems" and, with the §84 statistics record, its "diagnostics" point: the §39 ordered set of simulation systems.

The one revocable capability in the MVP, and the only one whose registry really supports removal: SystemRegistry.register returns an idempotent unregister and unregister(system) exists, so a plugin's own uninstall can put the registry back exactly as it found it. Every other §81 token keeps RFC 0002's conservative default (owner decision, Q3), which means a plugin that touches one of them cannot be uninstalled at all.

const plugin = {
  name: "@vendor/wind",
  version: "1.0.0",
  install(context) {
    context.require(SIMULATION_SYSTEMS).register(new WindSystem());
  },
};
const app = new Application({ plugins: [plugin] });
await app.initialize();
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(The plugin and context types live in @fourjs/core; naming them here would trip the §96 boundary test's textual ban, which is blunt on purpose.)

Provided by Application for every application that configures plugins: the registry is app.systems, which the application owns outright.