Migrates the 3 _bg_task closures in _cb_plan_epic and _cb_accept_tracks
plus the 2 try/except sites in _start_track_logic to proper Result[T]
propagation. Each worker closure now returns Result[None]; the
_start_track_logic helper wraps the whole pipeline.
New helper:
- _topological_sort_tickets_result(raw_tickets, title) -> Result[list]
(Phase 6 Group 6.7: dependency error is now a proper ErrorInfo
in the Result, not a silent debug log)
Audit: INTERNAL_SILENT_SWALLOW for src/app_controller.py: 17 -> 12.
ed
4ea6ea3988