fix: three measurement defects the adversarial triage surfaced

**COM discarded areas it had already read.** `entity_measure` fell back to
rebuilding geometry from `.Coordinates` when `.Area` *or* `.Length` was
missing, coupling two independent property reads. HATCH, REGION and 3DSOLID
expose `.Area` and neither of the others, so the fallback fired, found no
vertices, and raised "AutoCAD reported neither an area nor usable vertices" --
while holding the area. Those are the exact types the README sells the COM
backend on. Now only a missing `.Area` triggers the fallback; an absent
perimeter is reported as `None` with `perimeter_exact: False` instead of being
invented, which also removes a `round(None, 6)` TypeError waiting for the first
type that answers `.Area` and nothing else.

**A plain square hatch reported itself self-intersecting.** `ezdxf.path
.flattening()` repeats the start point, and `is_self_intersecting` excluded
adjacent edges *by index*, so with the duplicate present the first and last
real edges were cross-tested and registered as crossing. Measured: a 40x40
SOLID hatch came back `area: 1600.0, self_intersecting: True`. A closed loop
now answers the same whether or not it carries its closing vertex, and a real
bowtie is still caught (`area: 0.0, self_intersecting: True`).

**The bowtie warning never fired on the live backend.** `self_intersecting` was
only computed inside the COM fallback, so an LWPOLYLINE bowtie -- which has
both `.Area` and `.Length` and never reaches it -- returned `area: 0.0,
self_intersecting: null`. The confident zero this field exists to flag, going
out unflagged. It is now computed on the normal path too.

Also corrects a docstring written earlier today in `contracts/analysis.py`
claiming the live backend "asks AutoCAD for `.Area`, which has already applied
the [hatch island] style". Whether ActiveX's hatch area applies the style is
not verified against a live seat, and the method could not measure a hatch at
all. It now says so.

The ActiveX member profiles behind the COM tests are assumptions, not facts,
and the tests say so; a live seat settles them. `.Circumference` for CIRCLE and
`.Perimeter` for REGION are deliberately NOT added here -- writing more members
from the reference is what produced four wrong beliefs in v1.4/v1.5.

1267 passed, 1 xfailed.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

backends/com_backend.py

@@ -3197,7 +3197,14 @@ class ComBackend(AutoCADBackend):
             method = "activex_area"
             closed = True
             self_intersecting = None
-            if area is None or perimeter is None:
+            # Only the AREA decides whether we need the fallback. This used to
+            # read `area is None or perimeter is None`, which coupled two
+            # independent property reads: HATCH, REGION and 3DSOLID expose
+            # `.Area` but no `.Length`, so a perfectly good area was thrown
+            # away, the fallback demanded a `.Coordinates` only the polyline
+            # types carry, and the call died claiming AutoCAD "reported neither
+            # an area nor usable vertices" — while holding the area.
+            if area is None:
                 # Rebuild from the polyline's own vertices and run the SAME
                 # shared maths the headless engine uses, so a missing ActiveX
                 # property can never make this backend the less accurate one.
@@ -3214,15 +3221,33 @@ class ComBackend(AutoCADBackend):
                     )
                 closed = bool(getattr(ent, "Closed", True))
                 fallback_area, fallback_perimeter = polygon_area_perimeter(vertices, closed)
-                area = fallback_area if area is None else area
+                area = fallback_area
                 perimeter = fallback_perimeter if perimeter is None else perimeter
                 self_intersecting = is_self_intersecting([(v[0], v[1]) for v in vertices])
 
+            elif self_intersecting is None:
+                # The bowtie warning was only ever computed inside the fallback,
+                # so a live LWPOLYLINE bowtie — which has both `.Area` and
+                # `.Length` and therefore never reaches it — came back
+                # `area: 0.0, self_intersecting: null`. That is precisely the
+                # confident-zero this field exists to flag, going out unflagged.
+                coords = list(getattr(ent, "Coordinates", ()) or ())
+                if len(coords) >= 6:
+                    self_intersecting = is_self_intersecting(
+                        [
+                            (float(coords[i]), float(coords[i + 1]))
+                            for i in range(0, len(coords) - 1, 2)
+                        ]
+                    )
+
+            # A perimeter we do not have is reported as absent, not invented.
+            # `round(None, 6)` was also a TypeError waiting for the first type
+            # that answers `.Area` and nothing else.
             return {
                 "handle": str(handle),
                 "type": obj_name,
                 "area": round(float(area), 6),
-                "perimeter": round(float(perimeter), 6),
+                "perimeter": None if perimeter is None else round(float(perimeter), 6),
                 "closed": closed,
                 "assumed_closed": not closed,
                 "method": method,
@@ -3230,7 +3255,7 @@ class ComBackend(AutoCADBackend):
                 "flatten_tolerance": None,
                 "backend": "com",
                 "self_intersecting": self_intersecting,
-                "perimeter_exact": True,
+                "perimeter_exact": perimeter is not None,
                 "loop_count": 1,
             }