An entity sketch that forms no wire fails, instead of extruding a default box

entities_to_wire handles exactly two shapes: one lone closed entity
(Circle/Ellipse), or a chain of open ones (Line/Arc/EllipseArc/BSpline).
Anything else -- a circle coexisting with a line, two circles -- returns a
null wire. build_sketch_wire answered that by falling through to its
legacy tail, which ends in a rectangle built from width/height. For an
entity sketch those fields are whatever they were initialised to, so the
extrude produced a box the user never drew, silently and with ok:true.
That is how the ellipse+stray-arc case in the P2 Tier-B.1 verification
turned into a default-rectangle solid.

Throw there instead. The legacy profile/shape paths below are still
reached by sketches that legitimately carry no entities at all, so the
enum and profile constructors are untouched -- only the case where
entities exist and cannot be turned into a wire now fails, which is
exactly the case that was fabricating geometry.

This does NOT implement the multi-loop support the issue asks for. Doing
that properly means deciding containment -- a circle inside a rectangle is
a hole, a circle beside it is a second region -- and make_extrude_regions
cannot be reused because it takes flattened Vec2d contours for imported
Text/SVG art and would discard the analytic circle. Guessing containment
would trade a visible failure for a wrong solid, which is the opposite of
the point. Left scoped on snaporca-88v.

Also converts the three float comparisons in the two test cases added this
session from Approx to WithinAbs/WithinRel, per tests/CLAUDE.md, which
rules Approx out for being asymmetric and double-only. The rest of the
file's pre-existing Approx uses are left alone.

153 cases / 2090 assertions green on both forks; no existing test depended
on the default-rectangle fallback.

snaporca-88v (partial: the silent-fallback half).

tests/libslic3r/test_caddocument.cpp

@@ -6726,7 +6726,8 @@ TEST_CASE("A cut that removes no material is an error, not a silent success", "[
         // And the body is left as it was, not half-applied.
         CadDocument again = box();
         REQUIRE(again.recompute());
-        CHECK(again.body_mass_properties(0).volume == Approx(solid).margin(1e-6));
+        CHECK_THAT(again.body_mass_properties(0).volume,
+                   Catch::Matchers::WithinAbs(solid, 1e-6));
     }
 
     SECTION("the same hole on the body still works") {
@@ -6735,8 +6736,8 @@ TEST_CASE("A cut that removes no material is an error, not a silent success", "[
         const double solid = doc.body_mass_properties(0).volume;
         doc.add_hole(8.0, 20.0, true, 0.0, 0.0, SketchPlane::XY(), "Hole");
         REQUIRE(doc.recompute());
-        CHECK(doc.body_mass_properties(0).volume
-              == Approx(solid - M_PI * 16.0 * 20.0).epsilon(0.01));
+        CHECK_THAT(doc.body_mass_properties(0).volume,
+                   Catch::Matchers::WithinRel(solid - M_PI * 16.0 * 20.0, 0.01));
     }
 
     SECTION("a cut-mode extrude that misses is rejected too") {
@@ -6752,3 +6753,48 @@ TEST_CASE("A cut that removes no material is an error, not a silent success", "[
         CHECK(doc.error.find("removed no material") != std::string::npos);
     }
 }
+
+// entities_to_wire handles exactly two shapes: one lone closed entity, or a chain of open ones.
+// Anything else returns a null wire, and build_sketch_wire used to answer that by falling through
+// to its legacy tail — which ends in a rectangle built from width/height. For an entity sketch
+// those are whatever they were initialised to, so the extrude produced a box nobody drew.
+// snaporca-88v.
+TEST_CASE("An entity sketch that forms no wire fails instead of extruding a default box", "[CadDocument]")
+{
+    auto circle = [](Vec2d c, double r) {
+        SketchEntity e; e.type = SketchEntity::Type::Circle; e.center = c; e.p0 = c; e.radius = r;
+        return e;
+    };
+    auto line = [](Vec2d a, Vec2d b) {
+        SketchEntity e; e.type = SketchEntity::Type::Line; e.p0 = a; e.p1 = b;
+        return e;
+    };
+
+    SECTION("a lone circle still works — the supported case is untouched") {
+        CadDocument doc;
+        int sk = doc.add_sketch_entities({ circle({0, 0}, 10.0) }, SketchPlane::XY(), "Sketch");
+        doc.add_extrude(sk, 5.0, false, BooleanMode::New, "Extrude");
+        REQUIRE(doc.recompute());
+        CHECK_THAT(doc.body_mass_properties(0).volume,
+                   Catch::Matchers::WithinRel(M_PI * 100.0 * 5.0, 0.01));
+    }
+
+    SECTION("circle + stray line is rejected, not silently turned into a box") {
+        CadDocument doc;
+        int sk = doc.add_sketch_entities({ circle({0, 0}, 10.0), line({40, 40}, {60, 40}) },
+                                        SketchPlane::XY(), "Sketch");
+        doc.add_extrude(sk, 5.0, false, BooleanMode::New, "Extrude");
+        CHECK_FALSE(doc.recompute());
+        CHECK(doc.error.find("do not form a single closed wire") != std::string::npos);
+        CHECK(doc.bodies.empty());
+    }
+
+    SECTION("two circles are rejected too") {
+        CadDocument doc;
+        int sk = doc.add_sketch_entities({ circle({-20, 0}, 8.0), circle({20, 0}, 8.0) },
+                                        SketchPlane::XY(), "Sketch");
+        doc.add_extrude(sk, 5.0, false, BooleanMode::New, "Extrude");
+        CHECK_FALSE(doc.recompute());
+        CHECK(doc.error.find("do not form a single closed wire") != std::string::npos);
+    }
+}