A subtraction that removes nothing is an error, not a silent success

A boolean cut whose tool misses the target is a perfectly legal
operation: OCCT reports IsDone(), the shape comes back unchanged, and the
feature lands in the recipe reporting ok:true. Driving the MCP socket,
that produced two consecutive {ok: true, bodies: 1, error: ''} responses
for a hole that was never drilled -- same viewport, same 46939.11 mm3 --
and the tree grew two Hole features that will never cut anything. A
caller, an agent especially, has no signal at all that the thing it asked
for did not happen.

Measure the volume across the op in route_feature's in-place branch and
refuse the no-op. Only for removals: Hole, Thread, and Extrude / Revolve
/ Sweep / Loft in Cut mode. Everything else may legitimately leave the
volume alone -- a Transform certainly does. The tolerance is relative,
because an absolute epsilon is wrong across the mm-to-metre range of real
parts, and a cut that shaves a numerically invisible sliver is a miss
too. The existing rollback in the MCP actions already preserves the
reason, so a missed hole now answers ok:false with the error and undoes
the feature.

The confusion underneath was not itself a bug: hole's x/y are in the
sketch plane's frame, whose origin is describe_scene's modeling_origin,
and describe_tools documented them only as "number, unit mm". Passing the
world centre put the hole 135 mm clear of the solid. All six x/y params
on hole / hole_styled / hole_standard now say which frame they are in,
since the wrong guess was silent.

Regression test drives the reported failure directly: a hole at x=135 on
a 20x20x20 box is rejected and leaves the body untouched, the same hole
at the origin still removes exactly pi*4^2*20, and a cut-mode extrude
whose profile sits at x=200 is rejected too. 152 cases / 2083 assertions
green on both forks.

snaporca-daf.

src/slic3r/GUI/McpControl.cpp

@@ -159,8 +159,8 @@ json describe_tools()
                      json{{"name", "diameter"}, {"type", "number"}, {"unit", "mm"}, {"default", 5}, {"min", 0.01}},
                      json{{"name", "depth"},    {"type", "number"}, {"unit", "mm"}, {"default", 10}, {"min", 0.01}},
                      json{{"name", "through"},  {"type", "boolean"}, {"default", false}},
-                     json{{"name", "x"},        {"type", "number"}, {"unit", "mm"}, {"default", 0}},
-                     json{{"name", "y"},        {"type", "number"}, {"unit", "mm"}, {"default", 0}},
+                     json{{"name", "x"},        {"type", "number"}, {"unit", "mm"}, {"default", 0}, {"description", "in the sketch plane's frame (origin = describe_scene.modeling_origin), NOT world"}},
+                     json{{"name", "y"},        {"type", "number"}, {"unit", "mm"}, {"default", 0}, {"description", "in the sketch plane's frame (origin = describe_scene.modeling_origin), NOT world"}},
                      json{{"name", "plane"},    {"type", "string"}, {"enum", json::array({"XY", "XZ", "YZ"})}, {"default", "XY"}},
                  })}},
             json{{"name", "hole_styled"}, {"summary", "Drill a hole with optional counterbore (style=1) or countersink (style=2) at (x,y) on a plane."},
@@ -168,8 +168,8 @@ json describe_tools()
                      json{{"name", "diameter"},        {"type", "number"}, {"unit", "mm"}, {"default", 5}, {"min", 0.01}},
                      json{{"name", "depth"},           {"type", "number"}, {"unit", "mm"}, {"default", 10}, {"min", 0.01}},
                      json{{"name", "through"},         {"type", "boolean"}, {"default", true}},
-                     json{{"name", "x"},               {"type", "number"}, {"unit", "mm"}, {"default", 0}},
-                     json{{"name", "y"},               {"type", "number"}, {"unit", "mm"}, {"default", 0}},
+                     json{{"name", "x"},               {"type", "number"}, {"unit", "mm"}, {"default", 0}, {"description", "in the sketch plane's frame (origin = describe_scene.modeling_origin), NOT world"}},
+                     json{{"name", "y"},               {"type", "number"}, {"unit", "mm"}, {"default", 0}, {"description", "in the sketch plane's frame (origin = describe_scene.modeling_origin), NOT world"}},
                      json{{"name", "plane"},           {"type", "string"}, {"enum", json::array({"XY", "XZ", "YZ"})}, {"default", "XY"}},
                      json{{"name", "style"},           {"type", "integer"}, {"default", 0}, {"description", "0=simple, 1=counterbore, 2=countersink"}},
                      json{{"name", "cbore_diameter"},  {"type", "number"}, {"unit", "mm"}, {"default", 0}},
@@ -184,8 +184,8 @@ json describe_tools()
                      json{{"name", "style"},        {"type", "integer"}, {"default", 0}},
                      json{{"name", "through"},      {"type", "boolean"}, {"default", true}},
                      json{{"name", "depth"},        {"type", "number"}, {"unit", "mm"}, {"default", 10}, {"min", 0.01}},
-                     json{{"name", "x"},            {"type", "number"}, {"unit", "mm"}, {"default", 0}},
-                     json{{"name", "y"},            {"type", "number"}, {"unit", "mm"}, {"default", 0}},
+                     json{{"name", "x"},            {"type", "number"}, {"unit", "mm"}, {"default", 0}, {"description", "in the sketch plane's frame (origin = describe_scene.modeling_origin), NOT world"}},
+                     json{{"name", "y"},            {"type", "number"}, {"unit", "mm"}, {"default", 0}, {"description", "in the sketch plane's frame (origin = describe_scene.modeling_origin), NOT world"}},
                      json{{"name", "plane"},        {"type", "string"}, {"enum", json::array({"XY", "XZ", "YZ"})}, {"default", "XY"}},
                  })}},
             json{{"name", "boolean"}, {"summary", "Combine two bodies: union | subtract (tool from target) | intersect."},