[Clemens Koprolin (clemenskoprolin)]

This PR lets a server-rendered document contain multiple independently hydrated Compose HTML regions. HydrationRoot accepts an optional hydrationId and writes it to the root and its state element. hydrateRoot uses that ID to find the matching pair. Existing unnamed roots keep their behavior.

Hydration fails before deserializing state or changing the DOM when a named pair is missing or duplicated. Strict server-side validation also rejects duplicate hydration IDs.

Adds a hydration islands example and JVM, JS and Wasm tests for named roots and invalid pairs.

Fixes CMP-10871

Testing

Run from the html directory:

./gradlew -Pcompose.html.eap.enabled=true \
  :html-core-eap:jvmTest \
  :html-core-eap:jsBrowserTest \
  :html-core-eap:wasmJsBrowserTest \
  :html-eap-hydration-islands-example:jsBrowserDevelopmentWebpack \
  :html-eap-hydration-islands-example:wasmJsBrowserDevelopmentWebpack

Release Notes

N/A