- materialize artifact mentions into uploads-backed references before submit
- keep upload reference path behavior unchanged and mark failed artifact conversions stale
- add hooks tests for artifact/upload context availability and stabilize e2e mention selection path
- keep reference previews inside textarea area with dedicated UI
- replace reference cap and toast copy from 10 to 6
- add e2e coverage for sixth-limit blocking behavior
- trigger mention candidates when typing @ in any input position
- keep focus and input expansion after selecting a candidate
- anchor candidate panel to textarea area and update e2e selector assertions
肖应宇