--avoid-extrusion-cali-region

When --avoid-extrusion-cali-region is passed, the arrange engine registers a hard-coded rectangular zone along the front of the build plate as a "non-preferred" region before computing placement. Objects are steered away from this zone during auto-arrangement; they are not blocked from it entirely, which means a very large object that cannot fit elsewhere may still land partly inside it. Brim is explicitly exempted: the arrange engine forces zero inflation on the virtual obstacle because it is marked as an extrusion-calibration object, so brim strokes are allowed to overlap the zone while the object body itself is kept clear.

The zone is a fixed rectangle spanning x 18–240 mm, y 0–15 mm in bed coordinates. This nearly full-width front strip matches where the printer's extrusion-calibration and hand-eye-calibration routines deposit material during the first-layer sequence. The flag is a bool with a default of false, so arrangement ignores this strip unless the flag is explicitly set.

In the GUI's arrange and fill-bed paths the non-preferred zone is only injected when avoid_extrusion_cali_region is true *and* the machine profile's scan_first_layer option is also enabled. In fact the GUI goes further: the "Avoid extrusion calibration region" checkbox is hidden entirely and the flag is forced to false when scan_first_layer is off in the current printer profile. The CLI arrange path applies the zone whenever the flag is true, without checking scan_first_layer. This means passing --avoid-extrusion-cali-region on the CLI always protects the strip regardless of what the printer profile says about first-layer scanning.