[MNG-8112] Honor export descriptors from the extension classpath

[goutamadwant]

Fixes #10506.

Discover META-INF/maven/extension.xml from maven.ext.class.path entries and include their package and artifact exports in both CLI implementations. This makes exported packages visible to plugins and filters exported artifacts from plugin dependencies.

Reuse the existing descriptor reader. Keep extension classloader isolation and duplicate-extension precedence unchanged. Cover JARs, directories, multiple entries, optional descriptors, and loading alongside .mvn/extensions.xml.

Validation with JDK 21: both new Core ITs fail against the unmodified distribution and pass with the fix. mvn -B -ntp verify and the full mvn -B -ntp -Prun-its -Dits.forkCount=2 verify passed, including package-visibility and artifact-filtering regressions for both CLI implementations.

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[gnodet-bot]

Solid fix. The approach correctly reads extension.xml descriptors from -Dmaven.ext.class.path entries and feeds their exported packages/artifacts into CoreExports, so ClassRealmManager can properly filter them when building plugin realms. Both CLI implementations (compat 3.x and impl 4.x) are semantically equivalent despite their structural differences. The ordering is correct — setupContainerRealm already adds the classpath URLs to the container realm before discoverFrom is called, so descriptor scanning works against the right classloader. The list mutation in PlexusContainerCapsuleFactory is safe because setupContainerRealm makes a defensive copy.

Test coverage is thorough: unit tests verify package export visibility, artifact filtering, optional descriptors, and multi-entry classpath merging. The integration tests exercise both classpath-only and classpath-plus-extensions.xml scenarios end-to-end.

One nit below.

This review was generated by an AI agent, Hermès on behalf of @gnodet.

[gnodet-bot]

💡 Nit: @Deprecated marks this class itself as deprecated, which is not the intent — you want to suppress deprecation warnings from using the deprecated MavenCli. The correct annotation is @SuppressWarnings("deprecation").

Suggested change

	class MavenCliExtensionClasspathTest {
	@SuppressWarnings("deprecation")

[goutamadwant]

@gnodet-bot Replaced @Deprecated with @SuppressWarnings("deprecation"). The CLI tests and module verification pass. Thanks for catching this.

[gnodet-bot]

Re-review after 79dfab82: the @Deprecated → @SuppressWarnings("deprecation") nit from the previous review has been addressed. No new issues introduced.

This review was generated by an AI agent, Hermès on behalf of @gnodet.