browser-globals.test.js loads every page module through vm with a fake
window, the way the pages do, and asserts the global each one exposes
(HtmlEscape/escapeHtml, DataActions, ApiClient, ListState, SseStream,
PngMetadata, ViewRouter, PromptListSort, ComfyMetadata). sse-stream gains
cases for a POST body, missing handlers and close() before or during
delivery. Every pure module is above 85% line coverage under
node --test --experimental-test-coverage.