Handle synthetic AGP marker JARs in the local Google Maven proxy

[Copilot]

Copilot setup was still failing during Gradle warmup because the local Google Maven proxy only synthesized the com.android.application.gradle.plugin POM. Gradle also requests the marker JAR, and that request was falling through to blocked external hosts, aborting resolution of com.android.tools.build:gradle:8.5.2.

• Root cause

  • The proxy handled the AGP application marker POM but not the corresponding marker JAR.
  • Marker JAR requests therefore reached the normal mirror path and attempted external Google Maven access.

• Change

  • Extend the synthetic response path in tools/google_maven_proxy.py to also return an empty JAR for com.android.application.gradle.plugin.
  • Keep the existing synthetic POM behavior unchanged so Gradle still resolves the real dependency from com.android.tools.build:gradle.

• Effect

  • AGP marker resolution stays fully local during Copilot setup warmup.
  • Blocked DNS/network access to dl.google.com no longer breaks plugin classpath resolution for this marker.

• Illustrative snippet

  if request_path.endswith(".pom"):
      return "application/xml; charset=utf-8", pom
  
  if request_path.endswith(".jar"):
      return "application/java-archive", MirrorHandler.EMPTY_JAR_BYTES