- P2-6 tracking: global greedy IoU matching (all pairs, best overlap first)
replaces track-iteration-order greedy, so a crossing worker's box can no
longer be stolen by whichever track came first. Any track in a contended
match (person overlapping 2 tracks, or track overlapping 2 persons) is
reported via tracker.ambiguous(); run_once resets its detector + smoother
state so FALLEN/baseline/immobility never ride an id swap onto the wrong
person. A genuinely fallen worker re-confirms within prone_confirm_s.
- P2-7 fall: STANDING -> FALLING now requires sustained prone
(falling_confirm_s, 1.0s). One prone-looking frame (a bend, a bbox glitch)
no longer arms the ghost detector's CRITICAL if the person then leaves.
FALLEN / no_motion timing is unchanged (keyed off prone_since).
- P2-8 app: run_once feeds the engine and smoothers only tracks re-detected
this tick; a track coasting inside max_age with a frozen frame is no-data,
so prone-confirm / no-motion / immobility timers cannot accrue on stale
data. Re-detection still confirms the fall (dropout pauses evidence).
TDD: 7 new tests verified failing on the pre-fix code (git stash), then
203 passed / 2 skipped (hardware) with the fixes.
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