One entry of HealthPluginOptions.indicators: either a ready indicator instance or a factory that builds one from the service registry.

The factory arm exists because a health indicator often exists to probe a capability — the database, the broker — that the IHealthIndicator contract's argument-less check() cannot reach. The factory is called at the onInit phase, after every plugin has registered, so the capability it resolves is present regardless of plugin priority.

Named (rather than inlining the union) because the CLI's generated src/health/index.ts declares its array with this element type, and the renderer does not add the parentheses an inline union would need.