📝 Bug Description

The tracking-loss early return in src/services/exerciseEngine.ts does not update trackingLostFrames, visibilityBuffer, or lastValidAngles in the returned state object. On subsequent frames, the counter reads the stale value from currentState and never accurately increments, making the tracking-loss diagnostic counter unreliable during occlusion.

Bug location — src/services/exerciseEngine.ts:351-358 (approximate):

if (avgVisibility < 0.4 && nextTrackingLostFrames >= 5) {
  return {
    ...currentState,              // trackingLostFrames stays at previous value (e.g., 4)
    feedback: 'SENSORS BLURRED — POSITION BODY',
    status: 'yellow',
    isInExercisePosture: false,
    liveDepthFeedback: '',
    // MISSING: trackingLostFrames, visibilityBuffer, lastValidAngles
  };
}

The non-early-return path (lines ~738-740) correctly includes these:

return {
  ...currentState,
  // ...
  trackingLostFrames: nextTrackingLostFrames,
  visibilityBuffer: newVisibilityBuffer,
  lastValidAngles: nextLastValidAngles,
};

Steps To Reproduce

1. Start a workout
2. Occlude the camera so tracking is lost
3. trackingLostFrames increments to 4 (just below threshold of 5)
4. On the 5th frame, nextTrackingLostFrames >= 5 is true
5. Early return fires with only ...currentState (trackingLostFrames remains 4)
6. Counter stuck at 4 forever — every subsequent frame calculates nextTrackingLostFrames = 4 + 1 = 5, condition passes, early returns with trackingLostFrames: 4
7. Counter never reflects the actual duration of tracking loss

Expected Behavior

• Early return should override trackingLostFrames with the current nextTrackingLostFrames value
• visibilityBuffer and lastValidAngles should also be updated to avoid stale data

Actual Behavior

• trackingLostFrames counter stuck at 4 during sustained tracking loss
• visibilityBuffer also never updated — reappends to the same 4-element stale buffer
• No diagnostic impact on functionality (recovery still works), but diagnostic data is inaccurate

Browser

Chrome

Operating System

All

Node.js Version

v20.x

Additional Context

Impact: LOW-MEDIUM. The tracking-loss counter provides inaccurate data during sustained occlusion. Recovery is unaffected because the counter checks the condition correctly, but the returned state is stale.
Level: 1 (Beginner Friendly) — add missing state fields to early return