2.7.2rc16: Bug fixes and document updates

What's Changed

• [2.7] Fix receiver-side PASS_THROUGH channel mismatch for GET_TASK by @YuanTingHsieh in #4312
• [2.7] Fix auth test by @YuanTingHsieh in #4315
• [2.7] Fix Swarm deadlock: _executing guard prevents pipe handler replacement mid-transaction by @YuanTingHsieh in #4314
• [2.7] Condense 2.7.2 release notes to high-level feature highlights [skip ci] by @chesterxgchen in #4316

Full Changelog: 2.7.2rc15...2.7.2rc16