fix(webflux): register reactor hook in createWebFilter and add filter.

[amit306]

Fixes #17858

createWebFilter() and addFilter() now always register the Reactor
context propagation hook. The AndRegisterReactorHook variants are
deprecated and delegate to these methods.

[linux-foundation-easycla]

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[Copilot]

Pull request overview

Note

Copilot was unable to run its full agentic suite in this review.

This PR makes Spring WebFlux 5.3 client/server telemetry automatically register Reactor’s context-propagation hook and adds tests to verify OTel context survives a thread switch.

Changes:

• Register ContextPropagationOperator inside SpringWebfluxClientTelemetry.addFilter() and SpringWebfluxServerTelemetry.createWebFilter().
• Make the explicit “...AndRegisterReactorHook” APIs delegate to the now-hook-registering methods.
• Add unit tests asserting span context propagation across Schedulers.boundedElastic() thread switching.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 6 comments.

File	Description
instrumentation/spring/spring-webflux/spring-webflux-5.3/library/src/test/java/io/opentelemetry/instrumentation/spring/webflux/v5_3/ReactorHookRegistrationTest.java	Adds tests validating context propagation after hook auto-registration.
instrumentation/spring/spring-webflux/spring-webflux-5.3/library/src/main/java/io/opentelemetry/instrumentation/spring/webflux/v5_3/SpringWebfluxServerTelemetry.java	Auto-registers Reactor hook when creating the server WebFilter.
instrumentation/spring/spring-webflux/spring-webflux-5.3/library/src/main/java/io/opentelemetry/instrumentation/spring/webflux/v5_3/SpringWebfluxClientTelemetry.java	Auto-registers Reactor hook when adding the client ExchangeFilterFunction.

Comments suppressed due to low confidence (1)

instrumentation/spring/spring-webflux/spring-webflux-5.3/library/src/main/java/io/opentelemetry/instrumentation/spring/webflux/v5_3/SpringWebfluxClientTelemetry.java:50

• This now registers a global Reactor hook even when addFilter() returns early because the filter is already present. If the intent is to register the hook only when enabling instrumentation via this API, consider moving hook registration after the ‘already instrumented’ check, and/or guarding registration so it only happens once. This avoids repeated global work and reduces surprising side effects when callers invoke addFilter() defensively.

  public void addFilter(List<ExchangeFilterFunction> exchangeFilterFunctions) {
    ContextPropagationOperator.builder().build().registerOnEachOperator();
    for (ExchangeFilterFunction filterFunction : exchangeFilterFunctions) {
      if (filterFunction instanceof WebClientTracingFilter) {
        return;
      }