Upstream sync: port 15 commits from github/copilot-sdk (2026-03-15)#7

Copilot wants to merge 3 commits intomaingithub/copilot-sdk-java:mainfrom

copilot/upstream-sync-15-new-commitsgithub/copilot-sdk-java:copilot/upstream-sync-15-new-commitsCopy head branch name to clipboard