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.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01DfriM8XUkn7uYf5Dwe2xo6

CMakeLists.txt

@@ -65,6 +65,15 @@ target_link_libraries(_OCP PRIVATE
   TKOffset     # BRepOffsetAPI
   TKShHealing  # ShapeFix, ShapeAnalysis, ShapeUpgrade
   TKBool       # BRepAlgo helpers pulled in by the above
+  # Inc 3
+  TKXSBase     # XSControl, Interface, IFSelect
+  TKDESTEP     # STEPControl
+  TKDEIGES     # IGESControl, IGESData
+  TKDESTL      # RWStl
+  # Inc 4 — TKService carries the BRep font/text builders.  The builder image
+  # asserts it links without libGL/libX11, so this costs the runtime image
+  # nothing.
+  TKService
 )
 
 target_compile_definitions(_OCP PRIVATE