Feature: host-independent TracksOut with trajectory and lineage metadata #59

Goal

Introduce a semantic TracksOut type for scientific tools such as CellTracksColab, with native presentation in Napari and useful fallbacks in Fiji and QuPath. This is new feature work and was explicitly parked in the earlier Wave 2 spec PR #39; no claim that it already works.

Proposed minimal contract

• Tabular trajectory observations with track_id, t, y, x and optional z and feature columns, explicit zero-based frame indexing and units.
• Optional parent/child or branch relationship representation for tracks that split, merge or otherwise form lineages. Do not conflate a branch identifier with an entire lineage.
• ApplyTo("image") for image provenance, physical calibration and coordinate mapping when applicable.
• Napari renders native Tracks layers; other hosts can show a table/file until they have well-tested native trajectory viewers. Do not silently discard lineage semantics.
• Keep storage/provenance extensible to GEFF or other graph-based tracking standards without making them mandatory for every simple trajectory.

Acceptance criteria

• Representative moving tracks and branching lineages round-trip without losing track identity, frame, spatial coordinates or features.
• Napari visualization uses correct Z/T axis and world-space positioning.
• Fiji/QuPath fallback exposes the full underlying data and makes unavailable native rendering explicit.
• Tests cover missing IDs, nonfinite coordinates, unconnected lineages, branch structure, and large track tables.

Priority: Medium; defer until base axes and spatial provenance are correct.