Development backlog: development/remaining-issues.md

Open feature requests:
- Load and preserve unlabeled trajectories.
- Define residual/error information for IK and ID results.
- Consider per-container normalization methods; the time_normalize utility
  already normalizes equally spaced 1D signals to a percentage axis.

Subject grouping and caching are maintained and tested. The subject-level
filter dispatch problem is tracked as issue 10 in the development backlog.
