Loading PHP extensions
PHP reads extension declarations while it starts. In PHP.wasm, that means
extensions must be declared before loadNodeRuntime() or loadWebRuntime()
creates the runtime.
Use the extensions array for both bundled extensions and external .so
artifacts.
Use external PHP.wasm extensions when the code that must be fast or native-like is too hot for PHP userland, but you still want to ship it with a Playground demo, CLI workflow, or embedded app. The same manifest can be loaded by the JavaScript API, the Playground web Query API, and Playground CLI.
External extensions are JSPI side modules. If the browser or Node.js build does not expose JSPI, PHP.wasm rejects the extension request instead of starting with a partially loaded runtime.