Ladder rung 9: grade the engine against 50 real drawings, not against my taste

Ported from snaporca 5b82c846f3.

src/slic3r/GUI/CAD/DesignSketchTool.cpp

@@ -2311,7 +2311,7 @@ bool DesignSketchTool::try_add_constraints(const std::vector<SketchEntityConstra
     return false;
 }
 
-void DesignSketchTool::infer_auto_constraints(int base)
+void DesignSketchTool::infer_auto_constraints(int base, double ang_tol_rad)
 {
     const int n = int(m_entities.size());
     if (base < 0 || base >= n) return;
@@ -2357,7 +2357,7 @@ void DesignSketchTool::infer_auto_constraints(int base)
     //    so a single conflict never drops the others).
     for (int i = base; i < n; ++i) {
         if (m_entities[i].type != SketchEntity::Type::Line) continue;
-        auto ax = infer_axis_constraint(m_entities[i].p0, m_entities[i].p1);
+        auto ax = infer_axis_constraint(m_entities[i].p0, m_entities[i].p1, ang_tol_rad);
         if (!ax) continue;
         SketchEntityConstraintDef c;
         c.type = *ax;
@@ -8896,7 +8896,15 @@ int DesignSketchTool::add_entities_scripted(const std::vector<SketchEntity>& ent
     if (ents.empty()) return -1;
     const int base = int(m_entities.size());
     for (const SketchEntity& e : ents) m_entities.push_back(e);
-    infer_auto_constraints(base);   // the same auto-coincidence/H/V pass a gesture runs
+    // Auto-constrain, but do NOT let the inference move what the caller specified. A gesture
+    // gets 3 degrees of slack because a hand cannot click an exact horizontal; a scripted add
+    // has already said exactly what it means, and snapping a segment 2 degrees off to exactly
+    // horizontal silently rewrites it. Measured on a real drawing: feeding the 64 flattened
+    // segments of one circle moved vertices by up to 0.058 mm and shrank the enclosed area by
+    // 0.067%, because several segments of the polygon fell inside that 3 degree window. Exact
+    // coincidence inference is unaffected — it already tests to 1e-6 — so chains still weld
+    // and genuinely axis-aligned scripted geometry still gets its Horizontal/Vertical.
+    infer_auto_constraints(base, 1e-4);
     resolve_live();
     return base;
 }

src/slic3r/GUI/CAD/DesignSketchTool.hpp

@@ -628,7 +628,11 @@ private:
     // After entities [base, end) were committed, auto-emit the constraints that make
     // the new geometry stick: Coincident between co-located endpoints (so loops close
     // on their own) and Horizontal/Vertical on axis-aligned new segments.
-    void infer_auto_constraints(int base);
+    // ang_tol_rad is how far from an axis a segment may be and still be CALLED axis-aligned.
+    // A gesture needs the default 3 degrees — nobody clicks a horizontal line exactly — but
+    // that same slack MOVES geometry that was given exactly, so the scripted path passes a
+    // tolerance tight enough to recognise only what is already true. See add_entities_scripted.
+    void infer_auto_constraints(int base, double ang_tol_rad = 3.0 * M_PI / 180.0);
 
     // Selection helpers (Mode::Select).
     int hit_test(const Vec2d& p, double tol) const;       // nearest entity within tol, or -1

src/slic3r/GUI/CAD/McpControl.cpp

@@ -1204,18 +1204,30 @@ SketchEntity sketch_entity_from(const json& j)
         return Vec2d(a[0].get<double>(), a[1].get<double>());
     };
     e.construction = j.value("construction", false);
+    // A circle and an arc are defined BY their centre, so a request that does not carry one is
+    // incomplete, not a request for a circle at the origin. Defaulting it silently put geometry
+    // somewhere the caller never asked for and then reported perfectly consistent loops, areas
+    // and hole attribution ABOUT THAT WRONG GEOMETRY — which is far more expensive to disbelieve
+    // than an error would have been. `p0` is accepted as an alias because that is exactly what a
+    // circle stores internally (e.p0 = e.center below), so a caller who writes p0 means centre.
+    auto centre_of = [&](const char* what) {
+        if (j.contains("center")) return p("center", 0, 0);
+        if (j.contains("centre")) return p("centre", 0, 0);
+        if (j.contains("p0"))     return p("p0", 0, 0);
+        throw std::runtime_error(std::string(what) + " needs a 'center' (or 'p0')");
+    };
     if (t == "line") {
         e.type = SketchEntity::Type::Line;
         e.p0 = p("p0", 0, 0); e.p1 = p("p1", 0, 0);
     } else if (t == "circle") {
         e.type   = SketchEntity::Type::Circle;
-        e.center = p("center", 0, 0);
+        e.center = centre_of("circle");
         e.radius = j.value("radius", 0.0);
         e.p0     = e.center;
         if (e.radius <= 0.0) throw std::runtime_error("circle needs a positive 'radius'");
     } else if (t == "arc") {
         e.type        = SketchEntity::Type::Arc;
-        e.center      = p("center", 0, 0);
+        e.center      = centre_of("arc");
         e.radius      = j.value("radius", 0.0);
         e.start_angle = j.value("start_angle", 0.0);
         e.end_angle   = j.value("end_angle", 0.0);