All mutations run on the control thread through the existing stop, history and
prepared-plan workflow. No new dependencies are required.
## Phase 58 — Persistent Arrangement Markers
Edit/Markers/Set at cursor adds or renames a marker; Remove at cursor removes the exact tick key. Markers draw names and vertical guides in the arrangement and survive project save/load and undo. Up to 128 markers are supported. Names may overlap visually when markers are close; markers do not change playback by themselves.
View/Previous marker and Next marker navigate without wrapping and stop playback before seeking. Loop current section uses the last marker at or before the cursor through its successor; the final section ends at the final clip endpoint. Empty final sections reject. Loop ranges remain existing UI preferences rather than marker metadata.
