Runtime support and SSR
Choose the environment before deciding which client objects to share. The core delegates transport to native Fetch; storage and UI layers introduce additional platform and lifecycle assumptions.
| Environment | Prerequisite | Application responsibility |
|---|---|---|
| Browser HTTP | Fetch and the native request/response APIs used by the endpoint | Configure origin, CORS, cookies, and response validation with the server |
| Browser SSE | A readable response body and the stream APIs used by the pipeline | Own stream consumption and cancellation |
| Node consumer | Library manifests declare Node >=18.20.8 | Check the selected package and its actual dependency chain; this declaration is not a tested matrix for every tool |
| Repository development | Node >=20.20.2, pnpm 10.34.5 | Use the repository toolchain for building and tests |
| React / Viewer | Matching peer dependencies; repository catalog uses React/ReactDOM ^19.2.8, antd ^6.6.3, icons ^6.3.4, dayjs ^1.11.23 | Validate your framework and SSR import/render/hydration path; do not infer React 18 support |
Requirements come from packages/fetcher/package.json:31, package.json:39, pnpm-workspace.yaml:7, and the package manifests. Stream extraction checks the body in packages/eventstream/src/eventStreamResultExtractor.ts:38. Generator dependencies may impose stricter runtime requirements than a library's engine declaration.
Share configuration only within its intended identity scope
A client can be reused for stable service defaults, but its headers, timeout, and urlBuilder are mutable. The registrar is a module-global instance. In SSR, changing a shared client's authorization header for each incoming user request can expose one request's identity to another. Use request-scoped clients or pass identity through request options without mutating shared defaults; scope associated token/storage state as well. See packages/fetcher/src/fetcher.ts:127 and packages/fetcher/src/fetcherRegistrar.ts:166.
getStorage() uses browser localStorage when window exists and creates an in-memory implementation otherwise. That fallback does not establish a server request scope or cross-process persistence. Access to disabled localStorage is not caught by this path. Choose an explicit storage implementation and lifetime when those constraints matter. See packages/storage/src/env.ts:20 and storage runtime reference.
Treat Viewer state as application state
With a nonempty view list, Viewer reads window.location.pathname during render, before any effect runs. The current implementation therefore cannot render directly on a server without window. In an SSR application, mount Viewer (including FetcherViewer when it renders Viewer) behind a client-only render boundary and validate the actual import, render and hydration path. The empty-view early return does not establish SSR support for the complete Viewer. See packages/viewer/src/viewer/Viewer.tsx:296.
FetcherViewer creates default-view-ID storage at module scope with the fixed key fetcher-viewer-local-default-view-id. Viewer initializes the shared data monitor in an effect. These are reasons to inspect identity and resource lifetime, not a promise of stateless SSR components. See packages/viewer/src/fetcherviewer/FetcherViewer.tsx:94 and packages/viewer/src/viewer/Viewer.tsx:222.
Remounting a view when its definition, tenant, or owner changes separates UI state. The server must still enforce access control, and the application must scope persisted preferences appropriately. A particular SSR framework still needs import, render, and hydration validation; this chapter does not certify all frameworks.
Continue with shared clients, storage and events, and state ownership.
View Engine runtime
The view-engine package declares Node >=20.20.2. Its core entry is independent of React and browser globals; browser controls use the separate /react entry with React 19. ViewPage initializes and disposes its engine in Effects, while caller-owned engines must be scoped and disposed explicitly. Clipboard, page visibility and layout APIs remain browser capabilities. MemoryViewHost uses an optional shared Map for in-process examples and Node services. Browser persistence uses IndexedDBViewHost from the browser/React entry. Validate a framework-specific SSR/hydration integration instead of treating headless import support as certification of every UI component.