[PCrnjak]

A slow consumer of the legacy tracking stream can accumulate seconds of backlog. Add Tracker(mode="latest", max_frame_age=0.1) with a single replaceable unread frame and one thread owning source open/read/close. Reads wait for a distinct fresh frame; expired frames raise StaleFrameError if no replacement arrives by the deadline. The existing sequential default remains available for complete recording.

Expose immutable tracker.health snapshots in both modes: state, recent arrival FPS, local receipt age, frame/skip/duplicate/timeout counts, timestamp resets, hand count, and error details. Add CLI --latest, --max-frame-age, and --health; health JSON uses stderr, preserving frame output and recordings. Include a slow-consumer example and repeatable read-only benchmark.

Validation:

• The installed b2 wheel passed 107 tests on each Windows CPython 3.10.11, 3.11.9, 3.12.10, 3.13.17, 3.14.10, and 3.15.2. Each received 30 live frames in each mode, replayed the existing real-hand session, closed its worker, and passed pip dependency checks.
• Tests cover single-slot replacement, duplicate freshness, stale rejection, failures, EOF, source thread ownership, startup cleanup, reconnect, bounded shutdown, a close/read race, and CLI recording/health output.
• Two 20 Hz consumers ran on the Original Leap Motion Controller for ten seconds: sequential mode ended 7.39 seconds behind latest mode in the same service clock. Latest local receipt age was 6.40 ms median and 12.07 ms p95.
• A separate minute received 4,749 packets including warmup, with no read timeouts or tracking errors and clean close. Traced Python allocations peaked below 9 KB during measurement; native/service memory is excluded.
• Ruff, wheel/sdist builds, strict Twine metadata checks, and release artifact checks passed locally. Platform CI runs on this PR.

No hands were visible during the new live measurements; these establish delivery behavior, not full-skeleton CPU cost or absolute camera latency. Linux/macOS controller hardware and clean-Windows driver setup remain pending. See docs/LATEST_FRAMES.md for semantics and evidence.

The source version is 0.1.0b2 for the next release and reuses the immutable b1 engine download. PyPI currently provides 0.1.0b1.