fix(task-22): ucs_list decides "world" from the frame, not the empty name — an unnamed UCS is its own current row

An unnamed UCS (UCS Origin / 3P without saving, the common kind) has an
empty UCSNAME exactly like WCS does, so both engines answered
`current: world` while the drawing was not in WCS — verified live on
AutoCAD 2026 (`_.UCS _O 10,10,0` → UCSNAME="" WORLDUCS=0) and on the DXF
it writes ($UCSNAME='' $UCSORG=(0,20,0)). A silent wrong value.

- COM: a named match still wins; otherwise WORLDUCS (AutoCAD's own answer)
  decides, and WORLDUCS=0 appends a `name: None` row built from
  UCSORG/UCSXDIR/UCSYDIR.
- ezdxf: the same rule against $UCSORG/$UCSXDIR/$UCSYDIR via the new
  `engineering.environment.ucs.is_world_axes`; a stale $UCSNAME falls back
  to the frame instead of leaving no row current.
- Server `ucs_list` result: `current` is null for an unnamed UCS (never
  `world`), plus `current_unnamed: bool` so null is unambiguous.
- Tests: helper, headless (unnamed row, stale name, and the exact AutoCAD
  DXF over the wire), and COM fake reading WORLDUCS + the frame variables.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01FKFStjEFzpGyLq5bMpWxTd

backends/com_backend.py

@@ -1733,7 +1733,7 @@ class ComBackend(AutoCADBackend):
         }
 
     async def ucs_list(self) -> list[dict]:
-        from engineering.environment.ucs import WORLD
+        from engineering.environment.ucs import WORLD, WORLD_ORIGIN, WORLD_X_AXIS, WORLD_Y_AXIS
 
         def _sync():
             app = _acad_app()
@@ -1742,15 +1742,33 @@ class ComBackend(AutoCADBackend):
             rows = [
                 {
                     "name": WORLD,
-                    "origin": [0.0, 0.0, 0.0],
-                    "x_axis": [1.0, 0.0, 0.0],
-                    "y_axis": [0.0, 1.0, 0.0],
-                    "current": current == "",
+                    "origin": list(WORLD_ORIGIN),
+                    "x_axis": list(WORLD_X_AXIS),
+                    "y_axis": list(WORLD_Y_AXIS),
+                    "current": False,
                 }
             ]
             collection = doc.UserCoordinateSystems
             for index in range(int(collection.Count)):
                 rows.append(self._com_ucs_row(collection.Item(index), current))
+            if any(row["current"] for row in rows[1:]):
+                return rows
+            # No saved entry is current. UCSNAME is empty for an unnamed UCS
+            # (UCS Origin / 3P without saving) as well as for WCS — verified
+            # live (AutoCAD 2026: after `_.UCS _O 10,10,0`, UCSNAME="" and
+            # WORLDUCS=0). WORLDUCS is AutoCAD's own answer to "is this WCS".
+            if int(app.GetVariable("WORLDUCS")) == 1:
+                rows[0]["current"] = True
+            else:
+                rows.append(
+                    {
+                        "name": None,
+                        "origin": [float(c) for c in app.GetVariable("UCSORG")],
+                        "x_axis": [float(c) for c in app.GetVariable("UCSXDIR")],
+                        "y_axis": [float(c) for c in app.GetVariable("UCSYDIR")],
+                        "current": True,
+                    }
+                )
             return rows
 
         return await self._run(_sync)

backends/contracts/environment.py

@@ -86,7 +86,14 @@ class EnvironmentContract(ABC):
 
     @abstractmethod
     async def ucs_list(self) -> list[dict]:
-        """→ ``[{"name", "origin", "x_axis", "y_axis", "current": bool}]`` + the implicit "world"."""
+        """→ ``[{"name", "origin", "x_axis", "y_axis", "current": bool}]`` + the implicit "world".
+
+        Exactly one row is current. An *unnamed* current UCS (``UCS Origin`` /
+        ``3P`` without saving) is a trailing row with ``name: None`` carrying
+        its frame — "world" is current only when the frame is the WCS
+        (WORLDUCS live, the ``$UCS*`` header headless), never because the
+        name is empty.
+        """
         ...
 
     @abstractmethod

backends/ezdxf_backend.py

@@ -2692,22 +2692,41 @@ class EzdxfBackend(AutoCADBackend):
         }
 
     async def ucs_list(self) -> list[dict]:
-        from engineering.environment.ucs import WORLD
+        from engineering.environment.ucs import (
+            WORLD,
+            WORLD_ORIGIN,
+            WORLD_X_AXIS,
+            WORLD_Y_AXIS,
+            is_world_axes,
+        )
 
         def _sync():
             doc = self._require_doc()
-            current = str(doc.header.get("$UCSNAME", "") or "")
-            rows = [self._ucs_row(WORLD, (0, 0, 0), (1, 0, 0), (0, 1, 0), current == "")]
+            header = doc.header
+            current = str(header.get("$UCSNAME", "") or "")
+            origin = tuple(header.get("$UCSORG", WORLD_ORIGIN))
+            x_axis = tuple(header.get("$UCSXDIR", WORLD_X_AXIS))
+            y_axis = tuple(header.get("$UCSYDIR", WORLD_Y_AXIS))
+            rows = [self._ucs_row(WORLD, WORLD_ORIGIN, WORLD_X_AXIS, WORLD_Y_AXIS, False)]
+            named_current = False
             for ucs in doc.ucs:
+                is_current = current != "" and ucs.dxf.name.lower() == current.lower()
+                named_current = named_current or is_current
                 rows.append(
                     self._ucs_row(
-                        ucs.dxf.name,
-                        ucs.dxf.origin,
-                        ucs.dxf.xaxis,
-                        ucs.dxf.yaxis,
-                        current != "" and ucs.dxf.name.lower() == current.lower(),
+                        ucs.dxf.name, ucs.dxf.origin, ucs.dxf.xaxis, ucs.dxf.yaxis, is_current
                     )
                 )
+            if named_current:
+                return rows
+            # No saved entry is current. An empty $UCSNAME is NOT "world": an
+            # unnamed UCS (UCS Origin / 3P without saving) has an empty name
+            # too, and AutoCAD writes exactly that. The frame decides, the way
+            # WORLDUCS does live.
+            if is_world_axes(origin, x_axis, y_axis):
+                rows[0]["current"] = True
+            else:
+                rows.append(self._ucs_row(None, origin, x_axis, y_axis, True))
             return rows
 
         return await self._async(_sync)