Summary

Adds ESM static component assets so WebUI apps can keep the initial SSR payload small while loading deferred component trees asynchronously from a CDN or static folder without @microsoft/webui-router and without a template server.

webui build --emit-component-assets <tags> compiles requested lazy roots through synthetic non-entry fragments, keeping them out of the initial SSR entry graph while still emitting their full component dependency closure as static .webui.js modules.

What changed

• Emit one browser-native ESM asset per requested root, for example lazy-panel.webui.js.
  • The module default-exports template metadata, CSS module import maps, dependency closure metadata, and compiled condition functions together.
  • Static assets intentionally omit inventory state because they cannot know the page's current loaded template bitset.
• Add @microsoft/webui-framework/component-asset.js with defineComponentAssets().
  • Starts asset, component module, and optional data work together.
  • Skips importing when the root template is already registered.
  • Deduplicates in-flight imports and CSS module import maps.
  • Creates elements after asset/module work is ready and applies data later via setState() by default, with optional bounded data blocking.
• Move static component asset rendering into the Rust core API.
  • BuildOptions::component_asset_roots requests asset roots.
  • BuildResult::component_asset_files returns rendered [filename, ESM content] files.
  • render_component_assets() exposes the renderer for Rust callers.
  • build_to_disk() writes component assets alongside protocol.bin and CSS files.
• Expose the same build surface through Node/npm.
  • Node native builds accept componentAssetRoots.
  • build() returns flattened componentAssetFiles ([filename, content, ...]) in addition to cssFiles.
• Add generic emitted asset filename templating.
  • Reuses [name], [hash], [ext] for Link-mode CSS files and static component assets.
  • [ext] resolves to css for CSS and webui.js for component assets.
  • Protocol, CSS, and component asset filenames are validated together before writes, preventing partial output and overwrite collisions.
• Keep static .webui.js modules out of preload/link handling; only CSS assets use the existing CSS preload/link paths.
• Remove synthetic asset-root wrapper fragments before protocol serialization so asset-only wrappers do not bloat protocol.bin.
• Add examples/app/component-assets showing a no-router, no-template-server deferred component flow.
• Update DESIGN.md, CLI docs, Rust/Node integration docs, AI docs, interactivity docs, package READMEs, and framework docs.

Follow-ups filed

• Support scoped static component asset emission #364 — Support scoped static component asset emission for incremental/HMR and bundler-plugin flows.
• Deduplicate shared dependencies across static component assets #365 — Deduplicate shared dependencies across static component assets.

Validation

• cargo test -p microsoft-webui -p microsoft-webui-cli --lib
• cargo test -p microsoft-webui-cli
• cargo test -p microsoft-webui-node --lib
• cd packages/webui && pnpm build && pnpm test
• cargo xtask fmt
• cargo xtask clippy