Embedded web page race: host posts 'ready' before later <script>s run, so the native side's configure call is skipped

Setup: a native app (WKWebView, but the pattern applies to Electron and any webview) loads a page with several scripts. The first script (host.js) posts a 'ready' message to native, and native replies by opening a document. host.js then calls optional modules, if (window.app.feature) app.feature.configure(cfg). The modules are defined by later <script> tags.

Symptom: the feature is intermittently 'off' even with the setting on, in about 1 of 3 runs, depending on load.

Cause: the native reply can arrive before the browser has run the later scripts, so the feature-detect check sees undefined and silently skips configuration.

Fix: make each late module configure itself at load time from state the host already stored (host.config), as well as on the host's call, and make configure idempotent. Alternatively, post 'ready' only after the last script runs, e.g. from a final tiny script or on DOMContentLoaded.

Test that catches it: in the page test harness, inject the late script AFTER sending the open message and assert that the feature is configured. That fails deterministically before the fix, instead of 1 in 3.