Respect empty previous-build changelog and avoid backfilling older repo history

[Copilot]

When the latest prior build has an intentionally empty commit list, changelog collection could skip it and continue searching older builds, producing an oversized/full-history changelog. This change treats that empty list as authoritative and publishes an empty changelog for the new build.

• Changelog boundary behavior

  • In PublishToFillTask#gatherCommits, added an early return when the latest previous build’s commits list is empty.
  • This prevents fallback to older builds with commits and avoids traversing unrelated history.

• Implementation detail

  • Added hasLatestBuildWithEmptyCommits(List<BuildResponse>) to centralize and clarify the guard logic.

• Focused unit coverage

  • Added PublishToFillTaskTests for:
    • latest build has empty commits → guard triggers
    • latest build has commits → guard does not trigger
    • no builds → guard does not trigger

if (!builds.isEmpty()) {
  if (hasLatestBuildWithEmptyCommits(builds)) {
    return commits; // keep changelog empty by design
  }
  // existing previous-commit linear ancestry handling continues
}