bare-low/gpt-5-nano / tier-2-l-bracket

```openscad
// L-bracket: horizontal plate (X 0..50, Y 0..40, Z 0..3) and vertical plate (X 0..50, Y 0..3, Z 0..40)
// Inner corner at (0,0,0). Horizontal extends +Y, vertical extends +Z. All plates 3 mm thick.

// Hole and countersink parameters
hole_d = 4.5;          // through hole diameter
hole_h = 3;              // plate thickness (through the plate)
countersink_depth = 2;   // countersink depth (along outer direction)
countersink_r = 4;        // countersink outer diameter radius (8 mm diameter)

// Center positions for holes on each plate (10 mm from edges, centerline on face)
hole_xs = [10, 40];
hole_y = 20; // centerline for horizontal plate (along Y)
hole_ys = [10, 30];
hole_z = 20; // centerline for vertical plate (along Z)

$fn = 60;

// Main body: union of two orthogonal plates
difference() {
    // Base L-shaped solid: union of horizontal plate and vertical plate
    // Horizontal plate: 50 (X) x 40 (Y) x 3 (Z)
    translate([0, 0, 0])
        cube([50, 40, 3], center=false);
    // Vertical plate: 50 (X) x 3 (Y) x 40 (Z)
    translate([0, 0, 0])
        cube([50, 3, 40], center=false);
    
    // Subtract holes on horizontal plate (through Z)
    for (x = hole_xs) {
        // Hole center at (x, hole_y, Z from 0..3)
        translate([x, hole_y, 0])
            rotate([0,0,0])
                cylinder(h = 3, r = hole_d/2, center = false);
        // Countersink on outer top surface (Z direction)
        // Cone with base radius 4 at top surface Z=3, apex at Z=1
        translate([x, hole_y, 1])  // cone base starts at Z=1, top at Z=3
            rotate([0,0,0])
                cylinder(h = 2, r1 = 0, r2 = countersink_r, center = false);
    }
    // Subtract holes on vertical plate (through Y)
    for (zpos in [20, 20]) {
        // We'll place holes at (X, Y, Z) with Y hole axis; centers along X for each hole
        // Actually need two holes per vertical face: X positions 10 and 40, at Z center 20, along Y
        // Implement as separate two holes
    }
    // Vertical plate holes (cylinders along Y, through Y thickness 3)
    for (x = [10, 40]) {
        translate([x, 3, 20])
            rotate([0,90,0])
                cylinder(h = 3, r = hole_d/2, center = false);
        // Countersink along outer face at Y=3 (outer side)
        // Cone oriented along negative Y, base at Y=3, apex at Y=1
        translate([x, 1, 20])
            rotate([0,90,0])
                cylinder(h = 2, r1 = 0, r2 = countersink_r, center = false);
    }
}
```