fix(overlay): prevent usize underflow infinite loop in draw_text#55
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A detection whose label origin falls outside the overlay frame (e.g. a box that regressed just past the right edge, x=646 on a 640px frame) clamped copy_x_end below copy_x_start. The pixel-copy loop then computed copy_x_end - copy_x_start on usize, underflowing to ~2^64 and spinning a CPU core forever. Being inline, this backpressured the camera tee, froze the frame ring buffer, and froze every downstream consumer (HMI preview, frame capture). The same hazard existed on the y axis for labels past the bottom edge. Add clamp_copy_region(), which clamps the copy region in signed space and returns None when the label is entirely off-frame, guaranteeing start <= end so the unsigned subtraction can never underflow. Bail out of draw_text early when the origin is past the right/bottom edge. Add unit tests covering the regression and the straddling/off-frame edge cases.
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A detection whose label origin falls outside the overlay frame (e.g. a box that regressed just past the right edge, x=646 on a 640px frame) clamped copy_x_end below copy_x_start. The pixel-copy loop then computed copy_x_end - copy_x_start on usize, underflowing to ~2^64 and spinning a CPU core forever. Being inline, this backpressured the camera tee, froze the frame ring buffer, and froze every downstream consumer (HMI preview, frame capture). The same hazard existed on the y axis for labels past the bottom edge.
Add clamp_copy_region(), which clamps the copy region in signed space and returns None when the label is entirely off-frame, guaranteeing start <= end so the unsigned subtraction can never underflow. Bail out of draw_text early when the origin is past the right/bottom edge. Add unit tests covering the regression and the straddling/off-frame edge cases.