10C Inc 3 + 4: I/O and text — the app's whole OCP surface is bound

138/138 symbols across 53 modules. New: IFSelect, Interface, XSControl,
IGESData, STEPControl, IGESControl, RWStl, Graphic3d, NCollection, StdPrs.

**The full app suite passes against this wheel: 1797 passed, 1 skipped — the
same result as the stock wheel**, run from the parity venv.

Getting there needed six methods that no static analysis could have found:
`inventory --check` only sees symbols reached through an import, so a method
called on an instance is invisible to it. The suite found them in one pass, and
one of them (gp_Vec.Reverse, which every outward-normal probe calls) accounted
for 311 of the 255 failing tests on its own. The others: gp_Trsf.SetMirror over
a plane and a point, Geom_Surface.D0, BRep_Builder.MakeFace from a
triangulation, MakePipeShell.SetMode with a fixed binormal, and MakeFace from a
surface plus tolerance.

Open question **S5 is settled: no**. The wheel does not need OCCT's share/
resources. test_inc3_io.py asserts no CSF_* variable is set and then round-trips
STEP and IGES, reading the declared units back off both — which is exactly the
resource-less container the question was about.

The XSTEP readers keep the GIL, amending the blanket "file readers and writers"
line in design.md's GIL policy. STEP and IGES traffic in process-global
Interface_Static state, the IGES reader is documented as not thread-safe, and
the app already serialises imports behind a lock — so holding it costs nothing
and removes a class of question. RWStl, which touches no global state, releases.

XSControl_Reader and IGESData are registered although the app imports neither:
they are the reader base both concrete readers inherit their transfer surface
from, and the model-to-global-section chain the IGES unit probe walks.

src/modules/mod_IGESControl.cpp

@@ -0,0 +1,57 @@
+/*
+    OCP.IGESControl — IGES read and write.
+
+    The reader inherits its transfer surface from XSControl_Reader.  What is
+    specific here is the unit probe: the app reads the file's declared units
+    off the model's global section (IGESModel().GlobalSection().UnitName()),
+    which is why IGESData_IGESModel and IGESData_GlobalSection have to be
+    registered even though the app imports neither by name.
+
+    The writer is used only by the test suite, to produce IGES payloads to
+    import back; it is bound because those tests are part of the Inc 4 gate.
+
+    GIL held, per mod_XSControl.cpp — the IGES reader is explicitly documented
+    as not thread-safe.
+*/
+
+#include "../common/occt_module.h"
+#include "../common/occt_policies.h"
+
+#include <IGESControl_Controller.hxx>
+#include <IGESControl_Reader.hxx>
+#include <IGESControl_Writer.hxx>
+#include <IGESData_GlobalSection.hxx>
+#include <IGESData_IGESModel.hxx>
+#include <TCollection_HAsciiString.hxx>
+#include <TopoDS_Shape.hxx>
+#include <XSControl_Reader.hxx>
+
+void register_IGESControl(nb::module_ &root) {
+    nb::module_ m = ocp_submodule(root, "IGESControl");
+
+    nb::class_<IGESControl_Controller> controller(m, "IGESControl_Controller");
+    OCP_DEF_S(
+        controller, "Init", []() { return IGESControl_Controller::Init(); });
+
+    nb::class_<IGESControl_Reader, XSControl_Reader>(m, "IGESControl_Reader")
+        .def(nb::init<>())
+        .def("IGESModel", &IGESControl_Reader::IGESModel);
+
+    nb::class_<IGESControl_Writer>(m, "IGESControl_Writer")
+        .def(nb::init<>())
+        .def(nb::init<const Standard_CString, const Standard_Integer>(),
+             "unit_name"_a, "modecr"_a = 0)
+        // AddShape carries a Message_ProgressRange the app never supplies.
+        .def(
+            "AddShape",
+            [](IGESControl_Writer &self, const TopoDS_Shape &sh) {
+                return self.AddShape(sh);
+            },
+            "sh"_a, OCP_NOGIL)
+        .def("ComputeModel", &IGESControl_Writer::ComputeModel, OCP_NOGIL)
+        .def(
+            "Write",
+            [](IGESControl_Writer &self, const Standard_CString file,
+               const Standard_Boolean fnes) { return self.Write(file, fnes); },
+            "file"_a, "fnes"_a = Standard_False);
+}