feat(environment): portable layer states, named views and UCS on both engines

Layer states are ACADMCP_LAYERSTATES XRECORD chunks (<= 255 ASCII chars each),
in the file and not in AutoCAD's Layer States Manager. Headless view restore
writes the *Active VPORT (ezdxf's header has no $VIEWCTR; measured). UCS is
stored and made current; tool coordinates stay WCS.

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

README.md

@@ -27,8 +27,8 @@ Live through COM on Windows, or headless through ezdxf anywhere — one typed co
 
 </div>
 
-> **v1.5 release snapshot:** 169 tools · 8 resources · 5 prompt templates · 2423 collected tests.
+> **v1.5 release snapshot:** 179 tools · 8 resources · 5 prompt templates · 2423 collected tests.
-> 169 is the **registered** count; a default install advertises 164 over `tools/list`,
+> 179 is the **registered** count; a default install advertises 174 over `tools/list`,
 > because `ENABLE_3D` is unset. `system_about` is the runtime authority.
 
 ## Why this exists
@@ -104,7 +104,7 @@ Claude Desktop, Cursor, or any stdio MCP host. For HTTP: `autocad-mcp --transpor
 | Discovery | `search_tools` ranked over an AutoCAD command and synonym corpus — `FILLET`, `BPOLY`, `QSELECT`, `WBLOCK`, `OVERKILL`, `CHSPACE` each rank **#1** of the 161-tool advertised catalog |
 | Batching | `cad_batch` runs a step list in one round trip; `fields=` projects 11 result-heavy tools |
 | Paper space | tab lifecycle, viewports, `entity_change_space` (CHSPACE), `drawing_export_pdf(layout=…)` |
-| Environment | `document_list/activate/close` — several drawings open at once on both engines, the active one is what every tool targets |
+| Environment | `document_list/activate/close` — several drawings open at once on both engines; portable layer states (`ACADMCP_LAYERSTATES` XRECORDs — in the file, not in AutoCAD's Layer States Manager); named views; UCS stored and made current *(tool coordinates stay WCS)* |
 | Selection | window vs crossing stated back to the caller; a polygon tested against its own shape, not its bounding box |
 | Boundaries | `boundary_trace` (BOUNDARY/BPOLY) chains loose edges into one closed polyline, arcs kept as bulges *(headless)* |
 | Measurement | `analysis_measure_entity` measures what is *in* the drawing, by handle |

backends/com_backend.py

@@ -132,6 +132,14 @@ def _ai(values: list[int]):
     )
 
 
+def _avar(values):
+    """Create a VARIANT array of VARIANTs (what SetXRecordData takes for its values)."""
+    return win32com.client.VARIANT(
+        pythoncom.VT_ARRAY | pythoncom.VT_VARIANT,
+        list(values),
+    )
+
+
 def _solid_3d_capability() -> FeatureCapability:
     """3D solids are opt-in (ENABLE_3D=true) even on the live COM backend."""
     if config.settings.enable_3d:
@@ -815,6 +823,17 @@ class ComBackend(AutoCADBackend):
                 "solid_3d": _solid_3d_capability(),
                 "lisp": FeatureCapability(True, "sanitized"),
                 "documents": FeatureCapability(True, "native"),
+                # Spelling pinned by F Task 24's test_layer_states_are_declared_as_ours_not_autocads
+                # and quoted by the README and CLAUDE.md: mode "xrecord", this reason verbatim.
+                "layer_states": FeatureCapability(
+                    True,
+                    "xrecord",
+                    reason="portable_acadmcp_xrecord;not_listed_in_autocad_layer_states_manager",
+                ),
+                "named_views": FeatureCapability(True, "native"),
+                "ucs": FeatureCapability(
+                    True, "native", reason="world_restore_via_ucs_command;tool_coordinates_stay_wcs"
+                ),
                 "live_application": FeatureCapability(True, "native"),
                 "preferences": FeatureCapability(True, "native", reason="whitelisted_keys_only"),
                 "interactive_prompt": FeatureCapability(
@@ -1403,6 +1422,414 @@ class ComBackend(AutoCADBackend):
         await self._ensure_document_state()
         return result
 
+    # ── layer states ──────────────────────────────────────────────────────────
+
+    @staticmethod
+    def _com_layer_states(doc, *, create: bool):
+        from engineering.environment.layer_states import DICT_NAME
+
+        try:
+            return doc.Dictionaries.Item(DICT_NAME)
+        except Exception as exc:  # absent
+            log.debug("Dictionaries.Item(%s): %s", DICT_NAME, exc)
+        if not create:
+            return None
+        return doc.Dictionaries.Add(DICT_NAME)
+
+    @staticmethod
+    def _com_dict_entries(states) -> list[tuple[str, Any]]:
+        if states is None:
+            return []
+        out = []
+        for index in range(int(states.Count)):
+            obj = states.Item(index)
+            out.append((str(states.GetName(obj)), obj))
+        return out
+
+    def _com_layer_state_entry(self, states, name: str):
+        for key, obj in self._com_dict_entries(states):
+            if key.lower() == name.lower():
+                return key, obj
+        return None, None
+
+    @staticmethod
+    def _com_xrecord_chunks(xrecord) -> list[str]:
+        # pywin32 returns the two [out] parameters as a tuple, exactly as
+        # GetBoundingBox() / GetXData() do elsewhere in this file.
+        codes, values = xrecord.GetXRecordData()
+        return [
+            str(value)
+            for code, value in zip(list(codes or []), list(values or []), strict=False)
+            if int(code) == 1000
+        ]
+
+    @staticmethod
+    def _com_layer_snapshot(doc, description):
+        from engineering.environment.layer_states import snapshot_from_layers
+
+        current = str(doc.ActiveLayer.Name)
+        layers, plot = [], {}
+        for index in range(int(doc.Layers.Count)):
+            lyr = doc.Layers.Item(index)
+            layers.append(_layer_info(lyr, current))
+            plot[str(lyr.Name)] = bool(lyr.Plottable)
+        return snapshot_from_layers(layers, current, plot=plot, description=description)
+
+    async def layer_state_save(self, name, description=None) -> dict:
+        from engineering.environment.layer_states import encode_state, validate_state_name
+
+        clean = validate_state_name(name)
+        if description is not None and not isinstance(description, str):
+            raise TypeError("layer_state_save: description must be a string")
+
+        def _sync():
+            doc = _acad_doc()
+            state = self._com_layer_snapshot(doc, description)
+            chunks = encode_state(state)
+            states = self._com_layer_states(doc, create=True)
+            key, xrecord = self._com_layer_state_entry(states, clean)
+            replaced = xrecord is not None
+            if xrecord is None:
+                xrecord = states.AddXRecord(clean)
+                key = clean
+            xrecord.SetXRecordData(_ai([1000] * len(chunks)), _avar(chunks))
+            return {
+                "ok": True,
+                "name": key,
+                "layer_count": len(state["layers"]),
+                "replaced": replaced,
+                "chunks": len(chunks),
+                "backend": "com",
+            }
+
+        return await self._run(_sync)
+
+    async def layer_state_restore(self, name, properties=None) -> dict:
+        from engineering.environment.layer_states import (
+            decode_state,
+            diff_snapshot,
+            validate_properties,
+            validate_state_name,
+        )
+
+        clean = validate_state_name(name)
+        props = validate_properties(properties)
+
+        def _sync():
+            doc = _acad_doc()
+            states = self._com_layer_states(doc, create=False)
+            key, xrecord = self._com_layer_state_entry(states, clean)
+            if xrecord is None:
+                raise ValueError(
+                    f"layer_state_restore: no layer state named {clean!r}; "
+                    f"saved states: {[k for k, _ in self._com_dict_entries(states)]}"
+                )
+            state = decode_state(self._com_xrecord_chunks(xrecord))
+            current_name = str(doc.ActiveLayer.Name)
+            layers = [
+                _layer_info(doc.Layers.Item(i), current_name) for i in range(int(doc.Layers.Count))
+            ]
+            missing, new = diff_snapshot(state, layers)
+            current = None
+            warnings: list[str] = []
+            # Current first: AutoCAD refuses to freeze the active layer, so the
+            # active one must already be the state's before the loop freezes.
+            if "current" in props and state["current_layer"] not in missing:
+                doc.ActiveLayer = doc.Layers.Item(state["current_layer"])
+                current = state["current_layer"]
+            applied = 0
+            for layer_name, snap in state["layers"].items():
+                if layer_name in missing:
+                    continue
+                lyr = doc.Layers.Item(layer_name)
+                try:
+                    if "color" in props:
+                        lyr.Color = int(snap["color"])
+                    if "linetype" in props:
+                        _ensure_linetype_loaded(snap["linetype"])
+                        lyr.Linetype = snap["linetype"]
+                    if "lineweight" in props:
+                        lyr.LineWeight = int(snap["lineweight"])
+                    if "plot" in props:
+                        lyr.Plottable = bool(snap["plot"])
+                    if "on" in props:
+                        lyr.LayerOn = bool(snap["on"])
+                    if "frozen" in props:
+                        lyr.Freeze = bool(snap["frozen"])
+                    if "locked" in props:
+                        lyr.Lock = bool(snap["locked"])
+                except Exception as exc:  # e.g. freezing the active layer
+                    warnings.append(f"{layer_name}: {exc}")
+                    continue
+                applied += 1
+            _regen()
+            result = {
+                "ok": True,
+                "name": key,
+                "applied": {
+                    "layers": applied,
+                    "properties": list(props),
+                    "current_layer": current,
+                },
+                "missing_layers": missing,
+                "new_layers": new,
+                "backend": "com",
+            }
+            if warnings:
+                result["warnings"] = warnings
+            return result
+
+        return await self._run(_sync)
+
+    async def layer_state_list(self) -> list[dict]:
+        from engineering.environment.layer_states import decode_state
+
+        def _sync():
+            doc = _acad_doc()
+            states = self._com_layer_states(doc, create=False)
+            rows = []
+            for key, xrecord in self._com_dict_entries(states):
+                state = decode_state(self._com_xrecord_chunks(xrecord))
+                rows.append(
+                    {
+                        "name": key,
+                        "description": state.get("description"),
+                        "layer_count": len(state["layers"]),
+                    }
+                )
+            return rows
+
+        return await self._run(_sync)
+
+    async def layer_state_delete(self, name) -> dict:
+        from engineering.environment.layer_states import validate_state_name
+
+        clean = validate_state_name(name)
+
+        def _sync():
+            doc = _acad_doc()
+            states = self._com_layer_states(doc, create=False)
+            key, xrecord = self._com_layer_state_entry(states, clean)
+            if xrecord is None:
+                raise ValueError(
+                    f"layer_state_delete: no layer state named {clean!r}; "
+                    f"saved states: {[k for k, _ in self._com_dict_entries(states)]}"
+                )
+            removed = states.Remove(key)
+            try:
+                removed.Delete()
+            except Exception as exc:  # Remove already detached it
+                log.debug("XRecord.Delete after Remove: %s", exc)
+            return {"ok": True, "deleted": key, "backend": "com"}
+
+        return await self._run(_sync)
+
+    # ── named views ───────────────────────────────────────────────────────────
+
+    @staticmethod
+    def _com_view(doc, name: str):
+        try:
+            return doc.Views.Item(name)
+        except Exception:
+            return None
+
+    @staticmethod
+    def _com_view_row(view) -> dict:
+        center = view.Center
+        return {
+            "name": str(view.Name),
+            "center": [float(center[0]), float(center[1])],
+            "height": float(view.Height),
+            "width": float(view.Width),
+        }
+
+    async def view_named_save(self, name, center=None, height=None, width=None) -> dict:
+        from engineering.environment.names import validate_name
+        from engineering.environment.views import resolve_view_args
+
+        clean = validate_name(name, what="view name")
+        args = resolve_view_args(center, height, width)
+
+        def _sync():
+            doc = _acad_doc()
+            vport = doc.ActiveViewport
+            vp_center = vport.Center
+            vp_height = float(vport.Height) or 1.0
+            aspect = float(vport.Width) / vp_height if vp_height else 1.5
+            cx, cy = args["center"] or (float(vp_center[0]), float(vp_center[1]))
+            h = args["height"] or vp_height
+            w = args["width"] or h * aspect
+            view = self._com_view(doc, clean)
+            replaced = view is not None
+            if view is None:
+                view = doc.Views.Add(clean)
+            view.Center = _av([cx, cy])
+            view.Height = float(h)
+            view.Width = float(w)
+            return {
+                "ok": True,
+                "name": str(view.Name),
+                "center": [float(cx), float(cy)],
+                "height": float(h),
+                "width": float(w),
+                "replaced": replaced,
+                "backend": "com",
+            }
+
+        return await self._run(_sync)
+
+    async def view_named_restore(self, name) -> dict:
+        from engineering.environment.names import validate_name
+
+        clean = validate_name(name, what="view name")
+
+        def _sync():
+            doc = _acad_doc()
+            view = self._com_view(doc, clean)
+            if view is None:
+                names = [str(doc.Views.Item(i).Name) for i in range(int(doc.Views.Count))]
+                raise ValueError(
+                    f"view_named_restore: no named view {clean!r}; saved views: {names}"
+                )
+            row = self._com_view_row(view)
+            vport = doc.ActiveViewport
+            vport.Center = _av(row["center"])
+            vport.Height = row["height"]
+            vport.Width = row["width"]
+            # ActiveX applies viewport changes only when the object is assigned back.
+            doc.ActiveViewport = vport
+            _regen()
+            return {"ok": True, **row, "applied": "active_viewport", "backend": "com"}
+
+        return await self._run(_sync)
+
+    async def view_named_list(self) -> list[dict]:
+        def _sync():
+            doc = _acad_doc()
+            return [self._com_view_row(doc.Views.Item(i)) for i in range(int(doc.Views.Count))]
+
+        return await self._run(_sync)
+
+    # ── UCS ───────────────────────────────────────────────────────────────────
+
+    @staticmethod
+    def _com_ucs(doc, name: str):
+        try:
+            return doc.UserCoordinateSystems.Item(name)
+        except Exception:
+            return None
+
+    @staticmethod
+    def _com_ucs_row(ucs, current: str) -> dict:
+        return {
+            "name": str(ucs.Name),
+            "origin": [float(c) for c in ucs.Origin],
+            "x_axis": [float(c) for c in ucs.XVector],
+            "y_axis": [float(c) for c in ucs.YVector],
+            "current": current != "" and str(ucs.Name).lower() == current.lower(),
+        }
+
+    async def ucs_list(self) -> list[dict]:
+        from engineering.environment.ucs import WORLD
+
+        def _sync():
+            app = _acad_app()
+            doc = _acad_doc()
+            current = str(app.GetVariable("UCSNAME") or "")
+            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 == "",
+                }
+            ]
+            collection = doc.UserCoordinateSystems
+            for index in range(int(collection.Count)):
+                rows.append(self._com_ucs_row(collection.Item(index), current))
+            return rows
+
+        return await self._run(_sync)
+
+    async def ucs_set(self, name, origin, x_axis, y_axis) -> dict:
+        from engineering.environment.names import validate_name
+        from engineering.environment.ucs import WORLD, resolve_ucs_axes
+
+        clean = validate_name(name, what="UCS name")
+        if clean.lower() == WORLD:
+            raise ValueError("ucs_set: 'world' is reserved; ucs_restore('world') resets to WCS")
+        axes = resolve_ucs_axes(origin, x_axis, y_axis)  # refuses before any ActiveX call
+
+        def _sync():
+            doc = _acad_doc()
+            o, x, y = axes["origin"], axes["x_axis"], axes["y_axis"]
+            ucs = self._com_ucs(doc, clean)
+            replaced = ucs is not None
+            if ucs is None:
+                # ActiveX takes POINTS on the axes, not direction vectors.
+                ucs = doc.UserCoordinateSystems.Add(
+                    _apoint(*o),
+                    _apoint(o[0] + x[0], o[1] + x[1], o[2] + x[2]),
+                    _apoint(o[0] + y[0], o[1] + y[1], o[2] + y[2]),
+                    clean,
+                )
+            else:
+                ucs.Origin = _apoint(*o)
+                ucs.XVector = _apoint(*x)
+                ucs.YVector = _apoint(*y)
+            doc.ActiveUCS = ucs
+            return {
+                "ok": True,
+                "name": str(ucs.Name),
+                "origin": list(o),
+                "x_axis": list(x),
+                "y_axis": list(y),
+                "replaced": replaced,
+                "current": True,
+                "backend": "com",
+            }
+
+        return await self._run(_sync)
+
+    async def ucs_restore(self, name) -> dict:
+        from engineering.environment.names import validate_name
+        from engineering.environment.ucs import WORLD
+
+        clean = validate_name(name, what="UCS name")
+
+        def _sync():
+            app = _acad_app()
+            doc = _acad_doc()
+            if clean.lower() == WORLD:
+                # No ActiveX member selects WCS; the command does. Same guard as
+                # system_run_command: never send into an active prompt.
+                try:
+                    cmd_active = int(app.GetVariable("CMDACTIVE"))
+                except Exception as exc:
+                    log.debug("CMDACTIVE read failed, proceeding: %s", exc)
+                    cmd_active = 0
+                if cmd_active:
+                    raise RuntimeError(
+                        "AutoCAD has an active command or prompt (CMDACTIVE="
+                        f"{cmd_active}). Press ESC in AutoCAD to cancel, then retry."
+                    )
+                doc.SendCommand("_.UCS _W\n")
+                return {"ok": True, "name": WORLD, "current": True, "backend": "com"}
+            ucs = self._com_ucs(doc, clean)
+            if ucs is None:
+                names = [
+                    str(doc.UserCoordinateSystems.Item(i).Name)
+                    for i in range(int(doc.UserCoordinateSystems.Count))
+                ]
+                raise ValueError(
+                    f"ucs_restore: no UCS named {clean!r}; saved: {names} (or 'world')"
+                )
+            doc.ActiveUCS = ucs
+            return {"ok": True, "name": str(ucs.Name), "current": True, "backend": "com"}
+
+        return await self._run(_sync)
+
     # ── selection filters (M8 / F1) ──────────────────────────────────────────
     #
     # VERIFIED against a live AutoCAD 2026 (2026-08-05).

backends/contracts/environment.py

@@ -44,7 +44,60 @@ class EnvironmentContract(ABC):
         """
         ...
 
-    # ── layer states, named views, UCS: appended by Task 22 ──────────────────
+    # ── layer states (portable ACADMCP_LAYERSTATES XRECORDs, both engines) ──
+
+    @abstractmethod
+    async def layer_state_save(self, name: str, description: str | None = None) -> dict:
+        """→ ``{"ok", "name", "layer_count", "replaced"}``."""
+        ...
+
+    @abstractmethod
+    async def layer_state_restore(self, name: str, properties: list[str] | None = None) -> dict:
+        """``properties`` ⊆ {"on","frozen","locked","color","linetype","lineweight","plot","current"};
+        → ``{"ok", "name", "applied", "missing_layers", "new_layers"}``."""
+        ...
+
+    @abstractmethod
+    async def layer_state_list(self) -> list[dict]:
+        """→ ``[{"name", "description", "layer_count"}]``."""
+        ...
+
+    @abstractmethod
+    async def layer_state_delete(self, name: str) -> dict: ...
+
+    # ── named views ─────────────────────────────────────────────────────────
+
+    @abstractmethod
+    async def view_named_save(
+        self, name: str, center=None, height: float | None = None, width: float | None = None
+    ) -> dict:
+        """→ ``{"ok", "name", "center": [x, y], "height", "width", "replaced"}``."""
+        ...
+
+    @abstractmethod
+    async def view_named_restore(self, name: str) -> dict:
+        """ezdxf: sets the ``*Active`` VPORT, ``"applied": "header_only"``."""
+        ...
+
+    @abstractmethod
+    async def view_named_list(self) -> list[dict]: ...
+
+    # ── UCS (stored and made current; tool coordinates stay WCS) ────────────
+
+    @abstractmethod
+    async def ucs_list(self) -> list[dict]:
+        """→ ``[{"name", "origin", "x_axis", "y_axis", "current": bool}]`` + the implicit "world"."""
+        ...
+
+    @abstractmethod
+    async def ucs_set(self, name: str, origin, x_axis, y_axis) -> dict:
+        """non-orthogonal → ``ValueError`` with the measured angle."""
+        ...
+
+    @abstractmethod
+    async def ucs_restore(self, name: str) -> dict:
+        """``"world"`` resets."""
+        ...
 
     # ── application, preferences, operator prompts (COM only) ───────────────
 

backends/ezdxf_backend.py

@@ -1246,6 +1246,21 @@ class EzdxfBackend(AutoCADBackend):
                 ),
                 "lisp": FeatureCapability(False, reason="live_com_only"),
                 "documents": FeatureCapability(True, "registry"),
+                # Spelling pinned by F Task 24's test_layer_states_are_declared_as_ours_not_autocads
+                # and quoted by the README and CLAUDE.md: mode "xrecord", this reason verbatim.
+                "layer_states": FeatureCapability(
+                    True,
+                    "xrecord",
+                    reason="portable_acadmcp_xrecord;not_listed_in_autocad_layer_states_manager",
+                ),
+                "named_views": FeatureCapability(
+                    True,
+                    "vport_active",
+                    reason="restore_sets_the_view_the_file_opens_on;no_live_display",
+                ),
+                "ucs": FeatureCapability(
+                    True, "stored_not_interpreted", reason="tool_coordinates_stay_wcs"
+                ),
                 # Track E keys. `@capability` registers its key at import, and
                 # tests/test_capability_contract.py checks both maps from that
                 # moment on — so every key the contract module uses is declared
@@ -2312,6 +2327,431 @@ class EzdxfBackend(AutoCADBackend):
 
         return await self._async(_sync, quarantine_exit=closing_active)
 
+    # ── layer states ──────────────────────────────────────────────────────────
+
+    @staticmethod
+    def _layer_state_entry(states, name: str):
+        """Case-insensitive lookup → ``(stored_key, xrecord)`` or ``(None, None)``."""
+        if states is None:
+            return None, None
+        if name in states:
+            return name, states.get(name)
+        for key in states.keys():
+            if key.lower() == name.lower():
+                return key, states.get(key)
+        return None, None
+
+    @staticmethod
+    def _layer_state_chunks(xrecord) -> list[str]:
+        return [str(tag.value) for tag in xrecord.tags if tag.code == 1000]
+
+    @staticmethod
+    def _layer_states(doc):
+        from engineering.environment.layer_states import DICT_NAME
+
+        return doc.rootdict.get(DICT_NAME) if DICT_NAME in doc.rootdict else None
+
+    @staticmethod
+    def _layer_state_names(states) -> list[str]:
+        return list(states.keys()) if states is not None else []
+
+    def _layer_state_snapshot(self, doc, description):
+        from engineering.environment.layer_states import snapshot_from_layers
+
+        layers = [_layer_info_dxf(lyr, self._current_layer) for lyr in doc.layers]
+        plot = {lyr.dxf.name: bool(lyr.dxf.get("plot", 1)) for lyr in doc.layers}
+        return snapshot_from_layers(layers, self._current_layer, plot=plot, description=description)
+
+    async def layer_state_save(self, name, description=None) -> dict:
+        """Snapshot the layer table into ``ACADMCP_LAYERSTATES/<name>``.
+
+        Portable and file-resident; not an AutoCAD Layer States Manager entry.
+        """
+        from engineering.environment.layer_states import (
+            DICT_NAME,
+            encode_state,
+            validate_state_name,
+        )
+
+        clean = validate_state_name(name)
+        if description is not None and not isinstance(description, str):
+            raise TypeError("layer_state_save: description must be a string")
+
+        def _sync():
+            doc = self._require_doc()
+            state = self._layer_state_snapshot(doc, description)
+            chunks = encode_state(state)
+            states = doc.rootdict.get_required_dict(DICT_NAME)
+            existing_key, _ = self._layer_state_entry(states, clean)
+            replaced = existing_key is not None
+            if replaced:
+                states.remove(existing_key)
+            xrecord = states.add_xrecord(clean)
+            xrecord.extend([(1000, chunk) for chunk in chunks])
+            self._mark_dirty()
+            return {
+                "ok": True,
+                "name": clean,
+                "layer_count": len(state["layers"]),
+                "replaced": replaced,
+                "chunks": len(chunks),
+                "backend": "ezdxf",
+            }
+
+        return await self._async(_sync)
+
+    async def layer_state_restore(self, name, properties=None) -> dict:
+        from engineering.environment.layer_states import (
+            decode_state,
+            diff_snapshot,
+            validate_properties,
+            validate_state_name,
+        )
+
+        clean = validate_state_name(name)
+        props = validate_properties(properties)
+
+        def _sync():
+            doc = self._require_doc()
+            states = self._layer_states(doc)
+            key, xrecord = self._layer_state_entry(states, clean)
+            if xrecord is None:
+                raise ValueError(
+                    f"layer_state_restore: no layer state named {clean!r}; "
+                    f"saved states: {self._layer_state_names(states)}"
+                )
+            state = decode_state(self._layer_state_chunks(xrecord))
+            layers = [_layer_info_dxf(lyr, self._current_layer) for lyr in doc.layers]
+            missing, new = diff_snapshot(state, layers)
+            applied = 0
+            for layer_name, snap in state["layers"].items():
+                if layer_name not in doc.layers:
+                    continue  # missing: reported, never created
+                lyr = doc.layers.get(layer_name)
+                # Colour first: `Layer.color` keeps the on/off sign, and the
+                # on/off call below must see the final colour.
+                if "color" in props:
+                    lyr.color = int(snap["color"])
+                if "linetype" in props:
+                    _ensure_linetype_loaded(doc, snap["linetype"])
+                    lyr.dxf.linetype = snap["linetype"]
+                if "lineweight" in props:
+                    lyr.dxf.lineweight = int(snap["lineweight"])
+                if "plot" in props:
+                    lyr.dxf.plot = 1 if snap["plot"] else 0
+                if "on" in props:
+                    if snap["on"]:
+                        lyr.on()
+                    else:
+                        lyr.off()
+                if "frozen" in props:
+                    if snap["frozen"]:
+                        lyr.freeze()
+                    else:
+                        lyr.thaw()
+                if "locked" in props:
+                    if snap["locked"]:
+                        lyr.lock()
+                    else:
+                        lyr.unlock()
+                applied += 1
+            current = None
+            if "current" in props and state["current_layer"] in doc.layers:
+                current = state["current_layer"]
+                self._current_layer = current
+                doc.header["$CLAYER"] = current
+            self._mark_dirty()
+            return {
+                "ok": True,
+                "name": key,
+                "applied": {
+                    "layers": applied,
+                    "properties": list(props),
+                    "current_layer": current,
+                },
+                "missing_layers": missing,
+                "new_layers": new,
+                "backend": "ezdxf",
+            }
+
+        return await self._async(_sync)
+
+    async def layer_state_list(self) -> list[dict]:
+        from engineering.environment.layer_states import decode_state
+
+        def _sync():
+            doc = self._require_doc()
+            states = self._layer_states(doc)
+            rows = []
+            for key in self._layer_state_names(states):
+                state = decode_state(self._layer_state_chunks(states.get(key)))
+                rows.append(
+                    {
+                        "name": key,
+                        "description": state.get("description"),
+                        "layer_count": len(state["layers"]),
+                    }
+                )
+            return rows
+
+        return await self._async(_sync)
+
+    async def layer_state_delete(self, name) -> dict:
+        from engineering.environment.layer_states import validate_state_name
+
+        clean = validate_state_name(name)
+
+        def _sync():
+            doc = self._require_doc()
+            states = self._layer_states(doc)
+            key, xrecord = self._layer_state_entry(states, clean)
+            if xrecord is None:
+                raise ValueError(
+                    f"layer_state_delete: no layer state named {clean!r}; "
+                    f"saved states: {self._layer_state_names(states)}"
+                )
+            states.remove(key)
+            self._mark_dirty()
+            return {"ok": True, "deleted": key, "backend": "ezdxf"}
+
+        return await self._async(_sync)
+
+    # ── named views ───────────────────────────────────────────────────────────
+
+    # TEMPORARY (track-e/environment worktree only): group C's Task 14 defines
+    # the same `_active_vport` in its `# ── settings (track E, group C) ──`
+    # block, and C's is the one that ships. This copy exists so this worktree
+    # runs without C's code; the merge agent deletes THIS definition (two in
+    # one class are ruff F811, and the later one would silently win).
+    @staticmethod
+    def _active_vport(doc):
+        """The ``*Active`` VPORT entry — the view the file opens on. Created if absent."""
+        entries = doc.viewports.get("*Active")
+        if entries:
+            return entries[0]
+        return doc.viewports.new("*Active")
+
+    @staticmethod
+    def _view_entry(doc, name: str):
+        if name in doc.views:  # case-insensitive in ezdxf's table
+            return doc.views.get(name)
+        return None
+
+    async def view_named_save(self, name, center=None, height=None, width=None) -> dict:
+        from engineering.environment.names import validate_name
+        from engineering.environment.views import resolve_view_args
+
+        clean = validate_name(name, what="view name")
+        args = resolve_view_args(center, height, width)
+
+        def _sync():
+            doc = self._require_doc()
+            vport = self._active_vport(doc)
+            aspect = float(vport.dxf.get("aspect_ratio", 1.34)) or 1.34
+            if args["center"] is None or args["height"] is None:
+                # Headless there is no display to read a "current view" from;
+                # the drawing's extents are the honest default.
+                bb = ezdxf_bbox.extents(doc.modelspace()) if _BBOX_OK else None
+                if bb is None or not bb.has_data:
+                    raise ValueError(
+                        f"view_named_save: {clean!r} — an empty drawing has no extents; "
+                        "pass center and height"
+                    )
+                ext_center = (
+                    (bb.extmin.x + bb.extmax.x) / 2.0,
+                    (bb.extmin.y + bb.extmax.y) / 2.0,
+                )
+                # The window must hold the extents at the viewport's aspect:
+                # whichever side binds decides the height.
+                ext_height = max(bb.extmax.y - bb.extmin.y, (bb.extmax.x - bb.extmin.x) / aspect)
+                if ext_height <= 0:
+                    ext_height = 1.0
+            else:
+                ext_center, ext_height = args["center"], args["height"]
+            cx, cy = args["center"] or ext_center
+            h = args["height"] or ext_height
+            w = args["width"] or h * aspect
+            existing = self._view_entry(doc, clean)
+            replaced = existing is not None
+            stored = existing.dxf.name if replaced else clean
+            if replaced:
+                doc.views.remove(stored)
+            doc.views.add(stored, dxfattribs={"center": (cx, cy, 0.0), "height": h, "width": w})
+            self._mark_dirty()
+            return {
+                "ok": True,
+                "name": stored,
+                "center": [float(cx), float(cy)],
+                "height": float(h),
+                "width": float(w),
+                "replaced": replaced,
+                "backend": "ezdxf",
+            }
+
+        return await self._async(_sync)
+
+    async def view_named_restore(self, name) -> dict:
+        from engineering.environment.names import validate_name
+
+        clean = validate_name(name, what="view name")
+
+        def _sync():
+            doc = self._require_doc()
+            view = self._view_entry(doc, clean)
+            if view is None:
+                raise ValueError(
+                    f"view_named_restore: no named view {clean!r}; "
+                    f"saved views: {[v.dxf.name for v in doc.views]}"
+                )
+            cx, cy = float(view.dxf.center.x), float(view.dxf.center.y)
+            h, w = float(view.dxf.height), float(view.dxf.width)
+            vport = self._active_vport(doc)
+            vport.dxf.center = (cx, cy)
+            vport.dxf.height = h
+            if h > 0:
+                vport.dxf.aspect_ratio = w / h
+            self._mark_dirty()
+            return {
+                "ok": True,
+                "name": view.dxf.name,
+                "center": [cx, cy],
+                "height": h,
+                "width": w,
+                # The plan's literal. Measured: ezdxf's header refuses $VIEWCTR,
+                # so the store is the *Active VPORT — what AutoCAD reads as the
+                # initial view when it opens the file. No live display moves.
+                "applied": "header_only",
+                "store": "vport_active",
+                "backend": "ezdxf",
+            }
+
+        return await self._async(_sync)
+
+    async def view_named_list(self) -> list[dict]:
+        def _sync():
+            doc = self._require_doc()
+            return [
+                {
+                    "name": view.dxf.name,
+                    "center": [float(view.dxf.center.x), float(view.dxf.center.y)],
+                    "height": float(view.dxf.height),
+                    "width": float(view.dxf.width),
+                }
+                for view in doc.views
+            ]
+
+        return await self._async(_sync)
+
+    # ── UCS ───────────────────────────────────────────────────────────────────
+
+    @staticmethod
+    def _ucs_entry(doc, name: str):
+        for ucs in doc.ucs:
+            if ucs.dxf.name.lower() == name.lower():
+                return ucs
+        return None
+
+    @staticmethod
+    def _set_ucs_header(doc, name: str, origin, x_axis, y_axis) -> None:
+        doc.header["$UCSNAME"] = name
+        doc.header["$UCSORG"] = tuple(origin)
+        doc.header["$UCSXDIR"] = tuple(x_axis)
+        doc.header["$UCSYDIR"] = tuple(y_axis)
+
+    @staticmethod
+    def _ucs_row(name, origin, x_axis, y_axis, current: bool) -> dict:
+        return {
+            "name": name,
+            "origin": [float(c) for c in origin],
+            "x_axis": [float(c) for c in x_axis],
+            "y_axis": [float(c) for c in y_axis],
+            "current": current,
+        }
+
+    async def ucs_list(self) -> list[dict]:
+        from engineering.environment.ucs import WORLD
+
+        def _sync():
+            doc = self._require_doc()
+            current = str(doc.header.get("$UCSNAME", "") or "")
+            rows = [self._ucs_row(WORLD, (0, 0, 0), (1, 0, 0), (0, 1, 0), current == "")]
+            for ucs in doc.ucs:
+                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(),
+                    )
+                )
+            return rows
+
+        return await self._async(_sync)
+
+    async def ucs_set(self, name, origin, x_axis, y_axis) -> dict:
+        from engineering.environment.names import validate_name
+        from engineering.environment.ucs import WORLD, resolve_ucs_axes
+
+        clean = validate_name(name, what="UCS name")
+        if clean.lower() == WORLD:
+            raise ValueError("ucs_set: 'world' is reserved; ucs_restore('world') resets to WCS")
+        axes = resolve_ucs_axes(origin, x_axis, y_axis)  # refuses before any write
+
+        def _sync():
+            doc = self._require_doc()
+            existing = self._ucs_entry(doc, clean)
+            replaced = existing is not None
+            stored = existing.dxf.name if replaced else clean
+            if replaced:
+                doc.ucs.remove(stored)
+            doc.ucs.add(
+                stored,
+                dxfattribs={
+                    "origin": axes["origin"],
+                    "xaxis": axes["x_axis"],
+                    "yaxis": axes["y_axis"],
+                },
+            )
+            self._set_ucs_header(doc, stored, axes["origin"], axes["x_axis"], axes["y_axis"])
+            self._mark_dirty()
+            return {
+                "ok": True,
+                "name": stored,
+                "origin": list(axes["origin"]),
+                "x_axis": list(axes["x_axis"]),
+                "y_axis": list(axes["y_axis"]),
+                "replaced": replaced,
+                "current": True,
+                "backend": "ezdxf",
+            }
+
+        return await self._async(_sync)
+
+    async def ucs_restore(self, name) -> dict:
+        from engineering.environment.names import validate_name
+        from engineering.environment.ucs import WORLD
+
+        clean = validate_name(name, what="UCS name")
+
+        def _sync():
+            doc = self._require_doc()
+            if clean.lower() == WORLD:
+                self._set_ucs_header(doc, "", (0, 0, 0), (1, 0, 0), (0, 1, 0))
+                self._mark_dirty()
+                return {"ok": True, "name": WORLD, "current": True, "backend": "ezdxf"}
+            ucs = self._ucs_entry(doc, clean)
+            if ucs is None:
+                raise ValueError(
+                    f"ucs_restore: no UCS named {clean!r}; "
+                    f"saved: {[u.dxf.name for u in doc.ucs]} (or 'world')"
+                )
+            self._set_ucs_header(doc, ucs.dxf.name, ucs.dxf.origin, ucs.dxf.xaxis, ucs.dxf.yaxis)
+            self._mark_dirty()
+            return {"ok": True, "name": ucs.dxf.name, "current": True, "backend": "ezdxf"}
+
+        return await self._async(_sync)
+
     # ── viewports ────────────────────────────────────────────────────────────
 
     #: DXF viewport flag bit for "display locked" (VSF_LOCK_ZOOM).

discovery/aliases.py

@@ -74,6 +74,8 @@ class ToolAliases:
 #       class, a number and markers; a drafter typing it could mean either.
 #   CLOSE -- the active document (drawing_close) or one named document
 #       (document_close); a drafter typing it could mean either.
+#   LAYERSTATE, VIEW, UCS -- umbrella dialog/option commands (save, restore,
+#       list, delete in one) that this server splits into discrete tools.
 #
 # Every other AutoCAD command must map to exactly one tool.
 SHARED_ACAD_COMMANDS: frozenset[str] = frozenset(
@@ -84,11 +86,14 @@ SHARED_ACAD_COMMANDS: frozenset[str] = frozenset(
         "ERASE",
         "INSERT",
         "LAYER",
+        "LAYERSTATE",
         "LAYOUT",
         "MEASUREGEOM",
         "PLINE",
         "QSELECT",
         "SETVAR",
+        "UCS",
+        "VIEW",
         "ZOOM",
     }
 )
@@ -1466,6 +1471,85 @@ TOOL_ALIASES: dict[str, ToolAliases] = {
             "currently open files",
         ),
     ),
+    "layer_state_delete": ToolAliases(
+        acad=("LAYERSTATE",),
+        synonyms=("delete a layer state", "remove a saved layer setup", "drop the layer snapshot"),
+    ),
+    # Same rule as `document_list` above: no "which ... are" phrasings on the
+    # three list tools here — "which layer setups are saved" alone pushed
+    # `block_list` to #4 for the holdout "which blocks are defined" (measured
+    # 2026-09-17); the nouns carry the questions without the interrogative.
+    "layer_state_list": ToolAliases(
+        acad=("LAYERSTATE",),
+        synonyms=("saved layer states", "saved layer setups", "list layer snapshots"),
+    ),
+    "layer_state_restore": ToolAliases(
+        acad=("LAYERSTATE",),
+        synonyms=(
+            "restore the layer state",
+            "put the layers back",
+            "go back to the plot layer setup",
+            "reapply saved layer settings",
+            "layer snapshot restore",
+        ),
+    ),
+    "layer_state_save": ToolAliases(
+        acad=("LAYERSTATE",),
+        synonyms=(
+            "save the layer state",
+            "remember the layer setup",
+            "snapshot the layers",
+            "layer configuration for plotting",
+            "save which layers are frozen",
+        ),
+    ),
+    "ucs_list": ToolAliases(
+        acad=("UCS", "UCSMAN"),
+        synonyms=("the current ucs", "list coordinate systems", "named ucs", "ucs manager"),
+    ),
+    "ucs_restore": ToolAliases(
+        acad=("UCS",),
+        synonyms=(
+            "back to world coordinates",
+            "reset the ucs",
+            "ucs world",
+            "switch to a saved ucs",
+            "make that coordinate system current",
+        ),
+    ),
+    "ucs_set": ToolAliases(
+        acad=("UCS",),
+        synonyms=(
+            "user coordinate system",
+            "define a ucs",
+            "new coordinate system at this origin",
+            "rotate the ucs",
+            "ucs origin",
+        ),
+    ),
+    "view_named_list": ToolAliases(
+        acad=("VIEW",),
+        synonyms=("saved views", "existing named views", "list the views"),
+    ),
+    "view_named_restore": ToolAliases(
+        acad=("VIEW",),
+        synonyms=(
+            "go to the saved view",
+            "restore a named view",
+            "jump to the detail view",
+            "recall the view",
+        ),
+    ),
+    "view_named_save": ToolAliases(
+        acad=("VIEW",),
+        synonyms=(
+            "save this view",
+            "named view",
+            "remember where i am looking",
+            "bookmark the view",
+            "save a detail view",
+        ),
+    ),
 }
 
 

docs/tool-inventory.json

@@ -3,7 +3,7 @@
   "schema_version": 1,
   "package_version": "1.5.1",
   "totals": {
-    "tools": 169,
+    "tools": 179,
     "resources": 8,
     "prompts": 5,
     "groups": 20
@@ -19,7 +19,7 @@
     "entity_creation": 18,
     "entity_modification": 16,
     "entity_query": 9,
-    "layers": 14,
+    "layers": 18,
     "layouts": 12,
     "pid": 9,
     "premium": 12,
@@ -28,7 +28,7 @@
     "templates": 2,
     "transactions": 3,
     "validation": 1,
-    "view": 4
+    "view": 10
   },
   "tools": [
     {
@@ -1611,6 +1611,60 @@
         "title": "Show Layer"
       }
     },
+    {
+      "name": "layer_state_delete",
+      "group": "layers",
+      "cost": "destructive",
+      "summary": "Delete one saved layer state from the drawing.",
+      "tags": [
+        "layer"
+      ],
+      "annotations": {
+        "title": "Delete Layer State",
+        "destructiveHint": true
+      }
+    },
+    {
+      "name": "layer_state_list",
+      "group": "layers",
+      "cost": "read",
+      "summary": "List the layer states saved in this drawing.",
+      "tags": [
+        "layer"
+      ],
+      "annotations": {
+        "title": "List Layer States",
+        "readOnlyHint": true
+      }
+    },
+    {
+      "name": "layer_state_restore",
+      "group": "layers",
+      "cost": "safe",
+      "summary": "Restore a saved layer state, all properties or a chosen subset.",
+      "tags": [
+        "layer"
+      ],
+      "annotations": {
+        "title": "Restore Layer State",
+        "readOnlyHint": false,
+        "destructiveHint": false
+      }
+    },
+    {
+      "name": "layer_state_save",
+      "group": "layers",
+      "cost": "safe",
+      "summary": "Save the layer table (on/frozen/locked/colour/linetype/lineweight/plot + current) under a name, in the file.",
+      "tags": [
+        "layer"
+      ],
+      "annotations": {
+        "title": "Save Layer State",
+        "readOnlyHint": false,
+        "destructiveHint": false
+      }
+    },
     {
       "name": "layer_thaw",
       "group": "layers",
@@ -2251,6 +2305,47 @@
         "destructiveHint": true
       }
     },
+    {
+      "name": "ucs_list",
+      "group": "view",
+      "cost": "read",
+      "summary": "List the user coordinate systems, with the implicit world one.",
+      "tags": [
+        "view"
+      ],
+      "annotations": {
+        "title": "List UCS",
+        "readOnlyHint": true
+      }
+    },
+    {
+      "name": "ucs_restore",
+      "group": "view",
+      "cost": "safe",
+      "summary": "Make a saved UCS current, or `world` to reset to WCS.",
+      "tags": [
+        "view"
+      ],
+      "annotations": {
+        "title": "Restore UCS",
+        "readOnlyHint": false,
+        "destructiveHint": false
+      }
+    },
+    {
+      "name": "ucs_set",
+      "group": "view",
+      "cost": "safe",
+      "summary": "Define (or replace) a named UCS from an origin and two perpendicular axes, and make it current.",
+      "tags": [
+        "view"
+      ],
+      "annotations": {
+        "title": "Set UCS",
+        "readOnlyHint": false,
+        "destructiveHint": false
+      }
+    },
     {
       "name": "validation_check",
       "group": "validation",
@@ -2265,6 +2360,47 @@
         "readOnlyHint": true
       }
     },
+    {
+      "name": "view_named_list",
+      "group": "view",
+      "cost": "read",
+      "summary": "List the named views saved in this drawing.",
+      "tags": [
+        "view"
+      ],
+      "annotations": {
+        "title": "List Named Views",
+        "readOnlyHint": true
+      }
+    },
+    {
+      "name": "view_named_restore",
+      "group": "view",
+      "cost": "safe",
+      "summary": "Restore a named view.",
+      "tags": [
+        "view"
+      ],
+      "annotations": {
+        "title": "Restore Named View",
+        "readOnlyHint": false,
+        "destructiveHint": false
+      }
+    },
+    {
+      "name": "view_named_save",
+      "group": "view",
+      "cost": "safe",
+      "summary": "Save a named view: a centre and height (and width) to come back to.",
+      "tags": [
+        "view"
+      ],
+      "annotations": {
+        "title": "Save Named View",
+        "readOnlyHint": false,
+        "destructiveHint": false
+      }
+    },
     {
       "name": "view_screenshot",
       "group": "view",

engineering/environment/__init__.py

@@ -0,0 +1,16 @@
+"""Environment helpers (v1.6 track E): portable layer states, view and UCS
+argument resolution. Pure data and validation — no ezdxf, no COM."""
+
+from .layer_states import (  # noqa: F401
+    DICT_NAME,
+    PROPERTIES,
+    decode_state,
+    diff_snapshot,
+    encode_state,
+    snapshot_from_layers,
+    validate_properties,
+    validate_state_name,
+)
+from .names import validate_name  # noqa: F401
+from .ucs import WORLD, resolve_ucs_axes  # noqa: F401
+from .views import resolve_view_args  # noqa: F401

engineering/environment/layer_states.py

@@ -0,0 +1,122 @@
+"""Portable layer states: a layer-table snapshot <-> XRECORD string chunks.
+
+These are the server's own layer states, not AutoCAD's. AutoCAD keeps its
+Layer States Manager entries under the layer table's extension dictionary in
+a layout neither engine authors; this codec stores a JSON snapshot as
+1000-code string chunks in an XRECORD under the drawing's named object
+dictionary ``ACADMCP_LAYERSTATES``. They live in the file and travel with it,
+and they do **not** appear in AutoCAD's Layer States Manager (LAYERSTATE).
+That sentence is repeated in the tool docstrings, in ``system_capabilities``
+(feature ``layer_states``) and in the README.
+
+Chunks are ASCII (``ensure_ascii``), so a 255-character boundary can never
+split a code point, and 255 is AutoCAD's ``SetXRecordData`` string limit —
+ezdxf itself would accept longer tags (measured: a 300-character tag
+round-trips through save/reopen unchanged).
+"""
+
+from __future__ import annotations
+
+import json
+from typing import TYPE_CHECKING
+
+from .names import validate_name
+
+if TYPE_CHECKING:
+    from backends.base import LayerInfo
+
+DICT_NAME = "ACADMCP_LAYERSTATES"
+PROPERTIES = ("on", "frozen", "locked", "color", "linetype", "lineweight", "plot", "current")
+LAYER_PROPERTIES = PROPERTIES[:-1]
+CHUNK_SIZE = 255
+FORMAT_VERSION = 1
+
+
+def validate_state_name(name) -> str:
+    return validate_name(name, what="layer state name")
+
+
+def validate_properties(properties) -> tuple[str, ...]:
+    """The subset of ``PROPERTIES`` to apply; ``None`` means all of them."""
+    if properties is None:
+        return PROPERTIES
+    if isinstance(properties, str) or not isinstance(properties, (list, tuple)):
+        raise TypeError("properties must be a list of property names")
+    out: list[str] = []
+    for index, prop in enumerate(properties):
+        if prop not in PROPERTIES:
+            raise ValueError(f"properties[{index}]: {prop!r} is not one of {PROPERTIES}")
+        if prop not in out:
+            out.append(prop)
+    if not out:
+        raise ValueError(f"properties must name at least one of {PROPERTIES}")
+    return tuple(out)
+
+
+def snapshot_from_layers(
+    layers: list[LayerInfo],
+    current_layer: str,
+    *,
+    plot: dict[str, bool] | None = None,
+    description: str | None = None,
+) -> dict:
+    """The state dict for a layer table.
+
+    ``plot`` is per-layer plottability (``LayerInfo`` has no such field; each
+    engine reads it and passes it in), defaulting to plottable.
+    """
+    plot = plot or {}
+    return {
+        "version": FORMAT_VERSION,
+        "description": description,
+        "current_layer": str(current_layer),
+        "layers": {
+            layer.name: {
+                "on": bool(layer.is_on),
+                "frozen": bool(layer.is_frozen),
+                "locked": bool(layer.is_locked),
+                "color": int(layer.color),
+                "linetype": str(layer.linetype),
+                "lineweight": int(round(float(layer.lineweight))),
+                "plot": bool(plot.get(layer.name, True)),
+            }
+            for layer in layers
+        },
+    }
+
+
+def encode_state(state: dict) -> list[str]:
+    text = json.dumps(state, separators=(",", ":"), sort_keys=True, ensure_ascii=True)
+    return [text[i : i + CHUNK_SIZE] for i in range(0, len(text), CHUNK_SIZE)] or [""]
+
+
+def decode_state(chunks) -> dict:
+    text = "".join(str(chunk) for chunk in chunks)
+    try:
+        state = json.loads(text)
+    except ValueError as exc:
+        raise ValueError(f"layer state payload is not valid JSON: {exc}") from exc
+    if not isinstance(state, dict) or state.get("version") != FORMAT_VERSION:
+        found = state.get("version") if isinstance(state, dict) else type(state).__name__
+        raise ValueError(
+            f"layer state payload is not a version {FORMAT_VERSION} state (got {found!r})"
+        )
+    layers = state.get("layers")
+    if not isinstance(layers, dict):
+        raise ValueError("layer state payload has no 'layers' mapping")
+    for name, props in layers.items():
+        if not isinstance(props, dict):
+            raise ValueError(f"layer state entry {name!r} is not a mapping")
+        missing = [prop for prop in LAYER_PROPERTIES if prop not in props]
+        if missing:
+            raise ValueError(f"layer state entry {name!r} lacks {missing}")
+    state.setdefault("description", None)
+    state.setdefault("current_layer", "0")
+    return state
+
+
+def diff_snapshot(state: dict, layers: list[LayerInfo]) -> tuple[list[str], list[str]]:
+    """``(missing, new)``: in the state but not the drawing / in the drawing but not the state."""
+    in_state = set(state["layers"])
+    in_drawing = {layer.name for layer in layers}
+    return sorted(in_state - in_drawing), sorted(in_drawing - in_state)

engineering/environment/names.py

@@ -0,0 +1,17 @@
+"""One rule for the names this package stores in the drawing."""
+
+from __future__ import annotations
+
+
+def validate_name(name, *, what: str, max_len: int = 255) -> str:
+    """A non-empty, stripped string without control characters, else ``ValueError``."""
+    if not isinstance(name, str):
+        raise ValueError(f"{what} must be a string, got {type(name).__name__}")
+    clean = name.strip()
+    if not clean:
+        raise ValueError(f"{what} must not be empty")
+    if len(clean) > max_len:
+        raise ValueError(f"{what} is longer than {max_len} characters")
+    if any(ord(ch) < 32 for ch in clean):
+        raise ValueError(f"{what} must not contain control characters")
+    return clean

engineering/environment/ucs.py

@@ -0,0 +1,54 @@
+"""UCS axes, validated and normalised before either engine writes.
+
+Tool coordinates stay WCS on both engines (the repository rule): a UCS is
+stored and made current for the operator's benefit, and nothing here starts
+interpreting inputs in it.
+"""
+
+from __future__ import annotations
+
+import math
+
+WORLD = "world"
+ORTHO_TOLERANCE_DEG = 1e-3
+
+
+def _vec3(value, where: str) -> tuple[float, float, float]:
+    if not isinstance(value, (list, tuple)) or len(value) != 3:
+        raise ValueError(f"{where} must be an [x, y, z] triple")
+    out = []
+    for axis, item in zip("xyz", value, strict=True):
+        if isinstance(item, bool) or not isinstance(item, (int, float)):
+            raise ValueError(f"{where}.{axis} must be a number, got {item!r}")
+        number = float(item)
+        if not math.isfinite(number):
+            raise ValueError(f"{where}.{axis} must be finite")
+        out.append(number)
+    return out[0], out[1], out[2]
+
+
+def _unit(vector, where: str) -> tuple[float, float, float]:
+    length = math.sqrt(sum(c * c for c in vector))
+    if length < 1e-12:
+        raise ValueError(f"{where} must not be a zero vector")
+    return vector[0] / length, vector[1] / length, vector[2] / length
+
+
+def resolve_ucs_axes(origin, x_axis, y_axis) -> dict:
+    """Unit axes plus the measured angle; non-orthogonal axes are refused by that angle."""
+    o = _vec3(origin, "origin")
+    x = _unit(_vec3(x_axis, "x_axis"), "x_axis")
+    y = _unit(_vec3(y_axis, "y_axis"), "y_axis")
+    dot = max(-1.0, min(1.0, sum(a * b for a, b in zip(x, y, strict=True))))
+    angle = math.degrees(math.acos(dot))
+    if abs(angle - 90.0) > ORTHO_TOLERANCE_DEG:
+        raise ValueError(
+            f"ucs_set: x_axis and y_axis must be perpendicular; measured {angle:.2f}° "
+            f"between them (tolerance {ORTHO_TOLERANCE_DEG}°)"
+        )
+    z = (
+        x[1] * y[2] - x[2] * y[1],
+        x[2] * y[0] - x[0] * y[2],
+        x[0] * y[1] - x[1] * y[0],
+    )
+    return {"origin": o, "x_axis": x, "y_axis": y, "z_axis": z, "angle_deg": angle}

engineering/environment/views.py

@@ -0,0 +1,32 @@
+"""Named-view arguments, validated before either engine writes."""
+
+from __future__ import annotations
+
+import math
+
+
+def _finite(value, where: str) -> float:
+    if isinstance(value, bool) or not isinstance(value, (int, float)):
+        raise ValueError(f"{where} must be a number, got {value!r}")
+    number = float(value)
+    if not math.isfinite(number):
+        raise ValueError(f"{where} must be finite")
+    return number
+
+
+def resolve_view_args(center, height, width) -> dict:
+    """``{"center": (x, y) | None, "height": float | None, "width": float | None}``."""
+    out: dict = {"center": None, "height": None, "width": None}
+    if center is not None:
+        if not isinstance(center, (list, tuple)) or len(center) != 2:
+            raise ValueError("center must be an [x, y] pair")
+        out["center"] = (_finite(center[0], "center.x"), _finite(center[1], "center.y"))
+    if height is not None:
+        out["height"] = _finite(height, "height")
+        if out["height"] <= 0:
+            raise ValueError(f"height must be > 0, got {out['height']}")
+    if width is not None:
+        out["width"] = _finite(width, "width")
+        if out["width"] <= 0:
+            raise ValueError(f"width must be > 0, got {out['width']}")
+    return out

server.py

@@ -6819,7 +6819,7 @@ async def pid_tag_parse(
 
 
 # ---------------------------------------------------------------------------
-# ── SECTION 20: Environment (3 tools) ───────────────────────────────────────
+# ── SECTION 20: Environment (13 tools) ──────────────────────────────────────
 # ---------------------------------------------------------------------------
 
 
@@ -6904,6 +6904,207 @@ async def document_close(
     return await _backend(ctx).document_close(name_or_path, save, discard)
 
 
+@cad_tool(
+    summary="Save the layer table (on/frozen/locked/colour/linetype/lineweight/plot + current) under a name, in the file.",
+    cost="safe",
+)
+@mcp.tool(
+    annotations={"title": "Save Layer State", "readOnlyHint": False, "destructiveHint": False},
+    tags={"layer"},
+)
+async def layer_state_save(
+    name: Annotated[str, "State name, e.g. PLOT-SET or DESIGN"],
+    description: Annotated[str | None, "Free text stored with the state"] = None,
+    ctx: Context = None,
+) -> dict:
+    """Snapshot every layer's on/frozen/locked/color/linetype/lineweight/plot
+    flags plus the current layer as a named state stored in the drawing.
+
+    These are the server's own portable layer states: JSON chunks in an XRECORD
+    under the `ACADMCP_LAYERSTATES` dictionary. They live in the file and
+    travel with it, work on both engines, and do **not** appear in AutoCAD's
+    Layer States Manager (LAYERSTATE). Same name replaces (`replaced: true`).
+    Refusals: an empty or control-character name, a non-string description.
+    Pack: settings · lean: no.
+    """
+    await ctx.info(f"Saving layer state {name!r}")
+    return await _backend(ctx).layer_state_save(name, description)
+
+
+@cad_tool(summary="Restore a saved layer state, all properties or a chosen subset.", cost="safe")
+@mcp.tool(
+    annotations={"title": "Restore Layer State", "readOnlyHint": False, "destructiveHint": False},
+    tags={"layer"},
+)
+async def layer_state_restore(
+    name: Annotated[str, "A name from layer_state_list"],
+    properties: Annotated[
+        list[str] | None,
+        "Subset of on, frozen, locked, color, linetype, lineweight, plot, current; omit for all",
+    ] = None,
+    ctx: Context = None,
+) -> dict:
+    """Apply a saved state to the layers that still exist.
+
+    `missing_layers` (in the state, not in the drawing) are skipped, never
+    created; `new_layers` (in the drawing, not in the state) are untouched;
+    `applied` says how many layers and which properties moved. Refusals: an
+    unknown state name (lists the saved ones), a property outside the eight
+    (names the index). Live, a layer AutoCAD refuses to change (freezing the
+    active layer) lands in `warnings` instead of failing the call. Portable
+    server states, not Layer States Manager entries. Pack: settings · lean: no.
+    """
+    await ctx.info(f"Restoring layer state {name!r}")
+    return await _backend(ctx).layer_state_restore(name, properties)
+
+
+@cad_tool(summary="List the layer states saved in this drawing.", cost="read")
+@mcp.tool(
+    annotations={"title": "List Layer States", "readOnlyHint": True},
+    tags={"layer"},
+)
+async def layer_state_list(ctx: Context = None) -> dict:
+    """Every state under `ACADMCP_LAYERSTATES` with its description and layer
+    count. These are the server's portable states, not AutoCAD Layer States
+    Manager entries. No refusals. Pack: settings · lean: no."""
+    rows = await _backend(ctx).layer_state_list()
+    return {"states": rows, "count": len(rows)}
+
+
+@cad_tool(summary="Delete one saved layer state from the drawing.", cost="destructive")
+@mcp.tool(
+    annotations={"title": "Delete Layer State", "destructiveHint": True},
+    tags={"layer"},
+)
+async def layer_state_delete(
+    name: Annotated[str, "A name from layer_state_list"],
+    ctx: Context = None,
+) -> dict:
+    """Remove the named state's XRECORD. Layers themselves are untouched.
+    Refusal: an unknown name (lists the saved ones). Pack: settings · lean: no."""
+    await ctx.info(f"Deleting layer state {name!r}")
+    return await _backend(ctx).layer_state_delete(name)
+
+
+@cad_tool(
+    summary="Save a named view: a centre and height (and width) to come back to.", cost="safe"
+)
+@mcp.tool(
+    annotations={"title": "Save Named View", "readOnlyHint": False, "destructiveHint": False},
+    tags={"view"},
+)
+async def view_named_save(
+    name: Annotated[str, "View name, e.g. DETAIL-A"],
+    center: Annotated[
+        list[float] | None,
+        "[x, y] in WCS; default: the current view (live) or the drawing extents (headless)",
+    ] = None,
+    height: Annotated[float | None, "View height in drawing units; default as for center"] = None,
+    width: Annotated[
+        float | None, "View width; default: height × the current viewport aspect"
+    ] = None,
+    ctx: Context = None,
+) -> dict:
+    """Store a VIEW table entry (AutoCAD's VIEW command). Same name replaces
+    (`replaced: true`). Refusals: `height`/`width` ≤ 0 or non-finite, a
+    malformed `center`, and headless an empty drawing with no `center`/`height`
+    (there are no extents to default to). Pack: settings · lean: no."""
+    await ctx.info(f"Saving named view {name!r}")
+    return await _backend(ctx).view_named_save(name, center, height, width)
+
+
+@cad_tool(summary="Restore a named view.", cost="safe")
+@mcp.tool(
+    annotations={"title": "Restore Named View", "readOnlyHint": False, "destructiveHint": False},
+    tags={"view"},
+)
+async def view_named_restore(
+    name: Annotated[str, "A name from view_named_list"],
+    ctx: Context = None,
+) -> dict:
+    """Live: sets the active viewport to the saved centre/height/width
+    (`applied: "active_viewport"`). Headless there is no display: the saved
+    window is written to the `*Active` VPORT — the view AutoCAD opens the file
+    on — and the result says `applied: "header_only"`, the same reported-no-op
+    rule as `view_zoom_extents`. Refusal: an unknown name (lists the saved
+    views). Pack: settings · lean: no."""
+    return await _backend(ctx).view_named_restore(name)
+
+
+@cad_tool(summary="List the named views saved in this drawing.", cost="read")
+@mcp.tool(
+    annotations={"title": "List Named Views", "readOnlyHint": True},
+    tags={"view"},
+)
+async def view_named_list(ctx: Context = None) -> dict:
+    """Every VIEW table entry with centre, height and width. No refusals.
+    Pack: settings · lean: no."""
+    rows = await _backend(ctx).view_named_list()
+    return {"views": rows, "count": len(rows)}
+
+
+@cad_tool(summary="List the user coordinate systems, with the implicit world one.", cost="read")
+@mcp.tool(
+    annotations={"title": "List UCS", "readOnlyHint": True},
+    tags={"view"},
+)
+async def ucs_list(ctx: Context = None) -> dict:
+    """The `world` row first, then every UCS table entry with origin and unit
+    axes, `current` on the active one. Tool coordinates stay WCS on both
+    engines whatever is current. No refusals. Pack: settings · lean: no."""
+    rows = await _backend(ctx).ucs_list()
+    return {
+        "ucs": rows,
+        "count": len(rows),
+        "current": next((r["name"] for r in rows if r["current"]), None),
+    }
+
+
+@cad_tool(
+    summary="Define (or replace) a named UCS from an origin and two perpendicular axes, and make it current.",
+    cost="safe",
+)
+@mcp.tool(
+    annotations={"title": "Set UCS", "readOnlyHint": False, "destructiveHint": False},
+    tags={"view"},
+)
+async def ucs_set(
+    name: Annotated[str, "UCS name"],
+    origin: Annotated[list[float], "[x, y, z] in WCS"],
+    x_axis: Annotated[list[float], "Direction of the new X axis (any length)"],
+    y_axis: Annotated[list[float], "Direction of the new Y axis; must be perpendicular to x_axis"],
+    ctx: Context = None,
+) -> dict:
+    """Store a UCS table entry and make it current (AutoCAD's UCS command).
+
+    Axes are normalised to unit vectors. **Every tool keeps taking and
+    returning WCS coordinates** — the repository rule; a UCS is for the
+    operator's own drafting, and no tool starts interpreting inputs in it.
+    Refusals, before any write: a name of `world` (reserved), a zero-length
+    axis, and non-perpendicular axes — the message carries the measured angle
+    (tolerance 0.001°). Pack: settings · lean: no.
+    """
+    await ctx.info(f"Setting UCS {name!r}")
+    return await _backend(ctx).ucs_set(name, origin, x_axis, y_axis)
+
+
+@cad_tool(summary="Make a saved UCS current, or `world` to reset to WCS.", cost="safe")
+@mcp.tool(
+    annotations={"title": "Restore UCS", "readOnlyHint": False, "destructiveHint": False},
+    tags={"view"},
+)
+async def ucs_restore(
+    name: Annotated[str, "A name from ucs_list, or `world`"],
+    ctx: Context = None,
+) -> dict:
+    """Live: `ActiveUCS` for a named entry; `world` runs `UCS World`, which is
+    refused while AutoCAD has an active command (CMDACTIVE — press ESC).
+    Headless: the `$UCSNAME/$UCSORG/$UCSXDIR/$UCSYDIR` header variables.
+    Refusal: an unknown name (lists the saved ones). Tool coordinates stay
+    WCS. Pack: settings · lean: no."""
+    return await _backend(ctx).ucs_restore(name)
+
+
 # ---------------------------------------------------------------------------
 # ── RESOURCES ───────────────────────────────────────────────────────────────
 # ---------------------------------------------------------------------------

tests/test_layer_states.py

@@ -0,0 +1,444 @@
+"""Portable layer states: save → change → restore equals the snapshot.
+
+These are the server's own layer states — JSON chunks in an XRECORD under
+``ACADMCP_LAYERSTATES`` in the drawing's named object dictionary. They live
+in the file and travel with it; they do NOT appear in AutoCAD's Layer States
+Manager. The codec is engine-neutral, so the ezdxf tests prove the format and
+the COM tests prove the ActiveX call shapes.
+"""
+
+from __future__ import annotations
+
+import json
+import types
+
+import pytest
+
+from backends.base import LayerInfo
+from engineering.environment.layer_states import (
+    DICT_NAME,
+    PROPERTIES,
+    decode_state,
+    diff_snapshot,
+    encode_state,
+    snapshot_from_layers,
+    validate_properties,
+)
+
+pytestmark = pytest.mark.asyncio
+
+
+def _layer(name, **overrides) -> LayerInfo:
+    base = dict(
+        name=name,
+        color=7,
+        linetype="Continuous",
+        lineweight=-3,
+        is_on=True,
+        is_frozen=False,
+        is_locked=False,
+        is_current=False,
+    )
+    base.update(overrides)
+    return LayerInfo(**base)
+
+
+# ── codec ───────────────────────────────────────────────────────────────────
+
+
+def test_snapshot_records_every_property_and_the_current_layer():
+    state = snapshot_from_layers(
+        [_layer("0"), _layer("HIDDEN", color=8, linetype="HIDDEN", lineweight=35, is_frozen=True)],
+        "HIDDEN",
+        plot={"HIDDEN": False},
+        description="before plotting",
+    )
+    assert state == {
+        "version": 1,
+        "description": "before plotting",
+        "current_layer": "HIDDEN",
+        "layers": {
+            "0": {
+                "on": True,
+                "frozen": False,
+                "locked": False,
+                "color": 7,
+                "linetype": "Continuous",
+                "lineweight": -3,
+                "plot": True,
+            },
+            "HIDDEN": {
+                "on": True,
+                "frozen": True,
+                "locked": False,
+                "color": 8,
+                "linetype": "HIDDEN",
+                "lineweight": 35,
+                "plot": False,
+            },
+        },
+    }
+
+
+def test_encode_chunks_are_at_most_255_ascii_characters_and_round_trip():
+    layers = [_layer(f"LAYER-{i:03d}-{'x' * 40}") for i in range(60)]
+    state = snapshot_from_layers(layers, "0")
+    chunks = encode_state(state)
+    assert len(chunks) > 5
+    assert all(len(c) <= 255 and c.isascii() for c in chunks)
+    assert decode_state(chunks) == state
+
+
+def test_unicode_layer_names_survive_the_ascii_chunking():
+    state = snapshot_from_layers([_layer("KÖRPER-Ø20")], "KÖRPER-Ø20")
+    chunks = encode_state(state)
+    assert all(c.isascii() for c in chunks), "escaped so a chunk boundary never splits a code point"
+    assert decode_state(chunks)["current_layer"] == "KÖRPER-Ø20"
+
+
+@pytest.mark.parametrize(
+    "chunks, fragment",
+    [
+        (["not json"], "not valid JSON"),
+        ([json.dumps({"version": 2, "layers": {}})], "version"),
+        ([json.dumps({"version": 1, "layers": {"A": {"on": True}}})], "lacks"),
+        ([json.dumps([1, 2])], "version"),
+    ],
+)
+def test_decode_refuses_anything_that_is_not_a_state(chunks, fragment):
+    with pytest.raises(ValueError, match=fragment):
+        decode_state(chunks)
+
+
+def test_diff_reports_missing_and_new_layers_sorted():
+    state = snapshot_from_layers([_layer("A"), _layer("B"), _layer("C")], "0")
+    missing, new = diff_snapshot(state, [_layer("C"), _layer("Z"), _layer("A"), _layer("Y")])
+    assert missing == ["B"] and new == ["Y", "Z"]
+
+
+def test_validate_properties_defaults_to_all_and_names_the_bad_one():
+    assert validate_properties(None) == PROPERTIES
+    assert validate_properties(["color", "on", "color"]) == ("color", "on")
+    with pytest.raises(ValueError, match=r"properties\[1\]: 'colour'"):
+        validate_properties(["on", "colour"])
+    with pytest.raises(TypeError, match="list"):
+        validate_properties("on")
+    with pytest.raises(ValueError, match="at least one"):
+        validate_properties([])
+
+
+# ── headless engine ─────────────────────────────────────────────────────────
+
+
+async def _seed(backend):
+    await backend.layer_create("GEOMETRY", color=7, linetype="Continuous", lineweight=50)
+    await backend.layer_create("HIDDEN", color=8, linetype="HIDDEN", lineweight=35)
+    await backend.layer_create("CENTER", color=1, linetype="CENTER", lineweight=25)
+    await backend.layer_set_current("GEOMETRY")
+    await backend.layer_freeze("CENTER")
+    await backend.layer_hide("HIDDEN")
+
+
+async def _table(backend) -> dict:
+    return {
+        lyr.name: (
+            lyr.color,
+            lyr.linetype,
+            lyr.lineweight,
+            lyr.is_on,
+            lyr.is_frozen,
+            lyr.is_locked,
+            lyr.is_current,
+        )
+        for lyr in await backend.layer_list()
+    }
+
+
+async def test_save_change_restore_equals_the_snapshot(backend):
+    await _seed(backend)
+    before = await _table(backend)
+    saved = await backend.layer_state_save("PLOT", description="plot set")
+    # measured: ezdxf.new() already has "0" and "Defpoints", so the seeded
+    # table is five layers and serialises to three <= 255-character chunks
+    assert saved == {
+        "ok": True,
+        "name": "PLOT",
+        "layer_count": 5,
+        "replaced": False,
+        "chunks": 3,
+        "backend": "ezdxf",
+    }
+
+    await backend.layer_thaw("CENTER")
+    await backend.layer_show("HIDDEN")
+    await backend.layer_lock("GEOMETRY")
+    await backend.layer_modify("HIDDEN", color=3, linetype="Continuous", lineweight=13)
+    await backend.layer_set_current("0")
+    assert await _table(backend) != before
+
+    restored = await backend.layer_state_restore("PLOT")
+    assert restored["applied"] == {
+        "layers": 5,
+        "properties": list(PROPERTIES),
+        "current_layer": "GEOMETRY",
+    }
+    assert restored["missing_layers"] == [] and restored["new_layers"] == []
+    assert await _table(backend) == before
+
+
+async def test_restore_applies_only_the_requested_properties(backend):
+    await _seed(backend)
+    await backend.layer_state_save("S")
+    await backend.layer_thaw("CENTER")
+    await backend.layer_modify("CENTER", color=5)
+    result = await backend.layer_state_restore("S", properties=["color"])
+    assert result["applied"]["properties"] == ["color"]
+    center = next(lyr for lyr in await backend.layer_list() if lyr.name == "CENTER")
+    assert center.color == 1 and center.is_frozen is False, "frozen was not requested"
+
+
+async def test_restore_reports_missing_and_new_layers_and_never_creates(backend):
+    await _seed(backend)
+    await backend.layer_state_save("S")
+    await backend.layer_delete("CENTER")
+    await backend.layer_create("NEW-ONE")
+    result = await backend.layer_state_restore("S")
+    assert result["missing_layers"] == ["CENTER"] and result["new_layers"] == ["NEW-ONE"]
+    assert "CENTER" not in [lyr.name for lyr in await backend.layer_list()]
+
+
+async def test_plot_flag_and_current_layer_round_trip(backend):
+    await _seed(backend)
+    backend._doc.layers.get("HIDDEN").dxf.plot = 0
+    await backend.layer_state_save("S")
+    backend._doc.layers.get("HIDDEN").dxf.plot = 1
+    await backend.layer_set_current("0")
+    await backend.layer_state_restore("S", properties=["plot", "current"])
+    assert backend._doc.layers.get("HIDDEN").dxf.plot == 0
+    assert backend._current_layer == "GEOMETRY"
+    assert backend._doc.header["$CLAYER"] == "GEOMETRY"
+
+
+async def test_state_survives_save_and_reopen(backend, tmp_path):
+    await _seed(backend)
+    await backend.layer_state_save("PLOT", description="d")
+    path = tmp_path / "states.dxf"
+    await backend.drawing_save(str(path))
+    await backend.document_close(None)
+    await backend.drawing_open(str(path))
+    assert await backend.layer_state_list() == [
+        {"name": "PLOT", "description": "d", "layer_count": 5}
+    ]
+    await backend.layer_thaw("CENTER")
+    await backend.layer_state_restore("PLOT")
+    center = next(lyr for lyr in await backend.layer_list() if lyr.name == "CENTER")
+    assert center.is_frozen is True
+
+
+async def test_xrecord_chunks_stay_under_256_characters(backend):
+    for i in range(80):
+        await backend.layer_create(f"LONG-LAYER-NAME-{i:03d}-{'x' * 30}")
+    saved = await backend.layer_state_save("BIG")
+    assert saved["chunks"] > 10
+    xrecord = backend._doc.rootdict.get(DICT_NAME).get("BIG")
+    tags = [t for t in xrecord.tags if t.code == 1000]
+    assert len(tags) == saved["chunks"]
+    assert all(len(t.value) <= 255 for t in tags)
+
+
+async def test_replace_delete_and_missing_names(backend):
+    await backend.layer_state_save("S")
+    again = await backend.layer_state_save("s")
+    assert again["replaced"] is True, "AutoCAD dictionaries are case-insensitive"
+    assert [row["name"] for row in await backend.layer_state_list()] == ["s"]
+    assert await backend.layer_state_delete("S") == {"ok": True, "deleted": "s", "backend": "ezdxf"}
+    assert await backend.layer_state_list() == []
+    with pytest.raises(ValueError, match="no layer state named 'S'"):
+        await backend.layer_state_restore("S")
+    with pytest.raises(ValueError, match="no layer state named 'S'"):
+        await backend.layer_state_delete("S")
+
+
+async def test_refusals_happen_before_any_write(backend):
+    with pytest.raises(ValueError, match="layer state name"):
+        await backend.layer_state_save("   ")
+    with pytest.raises(TypeError, match="description"):
+        await backend.layer_state_save("S", description=3)
+    assert DICT_NAME not in backend._doc.rootdict, "a refused save creates no dictionary"
+    await backend.layer_state_save("S")
+    with pytest.raises(ValueError, match=r"properties\[0\]: 'plottable'"):
+        await backend.layer_state_restore("S", properties=["plottable"])
+    assert len(list(backend._doc.rootdict.get(DICT_NAME).keys())) == 1
+
+
+# ── live engine, against a fake ActiveX surface ──────────────────────────────
+
+
+class _FakeXRecord:
+    def __init__(self, name):
+        self.name = name
+        self.types = None
+        self.values = None
+        self.deleted = False
+
+    def SetXRecordData(self, types_, values):
+        self.types, self.values = list(types_), list(values)
+
+    def GetXRecordData(self):
+        return self.types, self.values
+
+    def Delete(self):
+        self.deleted = True
+
+
+class _FakeDict:
+    def __init__(self, name):
+        self.Name = name
+        self.entries: list[_FakeXRecord] = []
+        self.calls: list[tuple[str, tuple]] = []
+
+    @property
+    def Count(self):
+        return len(self.entries)
+
+    def Item(self, index):
+        return self.entries[index]
+
+    def GetName(self, obj):
+        return obj.name
+
+    def AddXRecord(self, keyword):
+        self.calls.append(("AddXRecord", (keyword,)))
+        rec = _FakeXRecord(keyword)
+        self.entries.append(rec)
+        return rec
+
+    def Remove(self, name):
+        self.calls.append(("Remove", (name,)))
+        rec = next(e for e in self.entries if e.name == name)
+        self.entries.remove(rec)
+        return rec
+
+
+class _FakeDictionaries:
+    def __init__(self):
+        self.dicts: dict[str, _FakeDict] = {}
+        self.calls: list[tuple[str, tuple]] = []
+
+    def Item(self, name):
+        self.calls.append(("Item", (name,)))
+        if name not in self.dicts:
+            raise RuntimeError(f"no dictionary {name}")
+        return self.dicts[name]
+
+    def Add(self, name):
+        self.calls.append(("Add", (name,)))
+        self.dicts[name] = _FakeDict(name)
+        return self.dicts[name]
+
+
+class _FakeLayer:
+    def __init__(self, name, **props):
+        self.Name = name
+        self.Color = props.get("color", 7)
+        self.Linetype = props.get("linetype", "Continuous")
+        self.LineWeight = props.get("lineweight", -3)
+        self.LayerOn = props.get("on", True)
+        self.Freeze = props.get("frozen", False)
+        self.Lock = props.get("locked", False)
+        self.Plottable = props.get("plot", True)
+
+
+class _FakeLayers:
+    def __init__(self, layers):
+        self._layers = layers
+
+    @property
+    def Count(self):
+        return len(self._layers)
+
+    def Item(self, key):
+        if isinstance(key, int):
+            return self._layers[key]
+        for lyr in self._layers:
+            if lyr.Name == key:
+                return lyr
+        raise RuntimeError(f"no layer {key}")
+
+
+@pytest.fixture
+def com_backend(monkeypatch):
+    pytest.importorskip("win32com.client", reason="pywin32 not installed")
+    from backends import com_backend as module
+
+    layers = [
+        _FakeLayer("0"),
+        _FakeLayer("GEOMETRY", lineweight=50),
+        _FakeLayer("HIDDEN", color=8, linetype="HIDDEN", frozen=True, plot=False),
+    ]
+    document = types.SimpleNamespace(
+        Dictionaries=_FakeDictionaries(),
+        Layers=_FakeLayers(layers),
+        ActiveLayer=layers[1],
+    )
+    monkeypatch.setattr(module, "_acad_doc", lambda: document)
+    monkeypatch.setattr(module, "_ensure_linetype_loaded", lambda name: None)
+    monkeypatch.setattr(module, "_regen", lambda: None)
+    monkeypatch.setattr(module, "_ai", lambda values: list(values))
+    monkeypatch.setattr(module, "_avar", lambda values: list(values))
+    backend = module.ComBackend()
+
+    async def _run_inline(func, *args, **kwargs):
+        return func(*args, **kwargs)
+
+    monkeypatch.setattr(backend, "_run", _run_inline)
+    return backend, document
+
+
+async def test_com_save_creates_the_dictionary_and_one_xrecord_of_1000_chunks(com_backend):
+    backend, document = com_backend
+    result = await backend.layer_state_save("PLOT", description="d")
+    assert result["ok"] and result["backend"] == "com" and result["replaced"] is False
+    assert document.Dictionaries.calls == [("Item", (DICT_NAME,)), ("Add", (DICT_NAME,))]
+    states = document.Dictionaries.dicts[DICT_NAME]
+    assert states.calls == [("AddXRecord", ("PLOT",))]
+    (rec,) = states.entries
+    assert rec.types == [1000] * len(rec.values)
+    assert all(len(v) <= 255 for v in rec.values)
+    state = decode_state(rec.values)
+    assert state["current_layer"] == "GEOMETRY"
+    assert state["layers"]["HIDDEN"]["plot"] is False
+    again = await backend.layer_state_save("plot")
+    assert again["replaced"] is True and again["name"] == "PLOT"
+    assert len(states.entries) == 1, "SetXRecordData on the existing record, no second AddXRecord"
+
+
+async def test_com_restore_reads_the_xrecord_and_writes_layer_properties(com_backend):
+    backend, document = com_backend
+    await backend.layer_state_save("S")
+    hidden = document.Layers.Item("HIDDEN")
+    hidden.Freeze = False
+    hidden.Color = 3
+    hidden.Plottable = True
+    document.ActiveLayer = document.Layers.Item("0")
+    result = await backend.layer_state_restore("S")
+    assert result["applied"]["layers"] == 3
+    assert result["applied"]["current_layer"] == "GEOMETRY"
+    assert hidden.Freeze is True and hidden.Color == 8 and hidden.Plottable is False
+    assert document.ActiveLayer.Name == "GEOMETRY"
+    assert result["missing_layers"] == [] and result["new_layers"] == []
+
+
+async def test_com_list_and_delete(com_backend):
+    backend, document = com_backend
+    await backend.layer_state_save("A", description="one")
+    await backend.layer_state_save("B")
+    assert await backend.layer_state_list() == [
+        {"name": "A", "description": "one", "layer_count": 3},
+        {"name": "B", "description": None, "layer_count": 3},
+    ]
+    assert (await backend.layer_state_delete("a"))["deleted"] == "A"
+    states = document.Dictionaries.dicts[DICT_NAME]
+    assert states.calls[-1] == ("Remove", ("A",))
+    with pytest.raises(ValueError, match="no layer state named 'A'"):
+        await backend.layer_state_delete("A")

tests/test_tool_registry.py

@@ -519,7 +519,10 @@ async def test_tool_group_sizes_are_unchanged():
     tag is ranked first in `_GROUP_TAG_PRIORITY` so those tools file under
     `pid` rather than under their secondary `query` / `create` tags. `drawing`
     moved 11 -> 14 when v1.6's `document_list` / `document_activate` /
-    `document_close` (multi-document on both engines) opened SECTION 20. Every
+    `document_close` (multi-document on both engines) opened SECTION 20;
+    `layers` moved 14 -> 18 with the four `layer_state_*` tools and `view`
+    4 -> 10 with `view_named_*` and `ucs_*` (UCS files under `view`, where
+    AutoCAD's own ribbon keeps it) when v1.6's SECTION 20 grew. Every
     other number here has been unchanged since the snapshot was taken.
     """
     sizes = {label: len(names) for label, names in (await server._tool_groups()).items()}
@@ -534,7 +537,7 @@ async def test_tool_group_sizes_are_unchanged():
         "entity_creation": 18,
         "entity_modification": 16,
         "entity_query": 9,
-        "layers": 14,
+        "layers": 18,
         "layouts": 12,
         "pid": 9,
         "premium": 12,
@@ -543,6 +546,6 @@ async def test_tool_group_sizes_are_unchanged():
         "templates": 2,
         "transactions": 3,
         "validation": 1,
-        "view": 4,
+        "view": 10,
     }
-    assert sum(sizes.values()) == 169
+    assert sum(sizes.values()) == 179

tests/test_views_ucs.py

@@ -0,0 +1,338 @@
+"""Named views and UCS on both engines.
+
+Headless, a named view is a VIEW table entry and "restore" writes the
+``*Active`` VPORT (the view the file opens on) — ezdxf's header has no
+``$VIEWCTR``; measured. A UCS is a UCS table entry plus the ``$UCS*`` header
+variables. Tool coordinates stay WCS on both engines: a UCS is stored and
+made current for the operator, and no tool interprets its inputs in it.
+"""
+
+from __future__ import annotations
+
+import types
+
+import pytest
+
+from engineering.environment.ucs import resolve_ucs_axes
+from engineering.environment.views import resolve_view_args
+
+pytestmark = pytest.mark.asyncio
+
+
+# ── pure helpers ────────────────────────────────────────────────────────────
+
+
+def test_view_args_validate_before_any_write():
+    assert resolve_view_args([10, 20], 50, None) == {
+        "center": (10.0, 20.0),
+        "height": 50.0,
+        "width": None,
+    }
+    assert resolve_view_args(None, None, None) == {"center": None, "height": None, "width": None}
+    with pytest.raises(ValueError, match="height must be > 0"):
+        resolve_view_args(None, 0, None)
+    with pytest.raises(ValueError, match="width must be > 0"):
+        resolve_view_args(None, 10, -1)
+    with pytest.raises(ValueError, match="center"):
+        resolve_view_args([1], None, None)
+    with pytest.raises(ValueError, match="finite"):
+        resolve_view_args([float("nan"), 0], None, None)
+
+
+def test_ucs_axes_are_normalised_and_orthogonality_is_measured():
+    axes = resolve_ucs_axes([10, 10, 0], [0, 2, 0], [-3, 0, 0])
+    assert axes["origin"] == (10.0, 10.0, 0.0)
+    assert axes["x_axis"] == (0.0, 1.0, 0.0) and axes["y_axis"] == (-1.0, 0.0, 0.0)
+    assert axes["z_axis"] == (0.0, 0.0, 1.0)
+    assert axes["angle_deg"] == pytest.approx(90.0)
+    with pytest.raises(ValueError, match=r"measured 45\.00"):
+        resolve_ucs_axes([0, 0, 0], [1, 0, 0], [1, 1, 0])
+    with pytest.raises(ValueError, match="x_axis.*zero"):
+        resolve_ucs_axes([0, 0, 0], [0, 0, 0], [0, 1, 0])
+    with pytest.raises(ValueError, match="origin"):
+        resolve_ucs_axes([0, 0], [1, 0, 0], [0, 1, 0])
+
+
+# ── headless: named views ───────────────────────────────────────────────────
+
+
+async def test_view_defaults_to_the_drawing_extents(backend):
+    await backend.entity_create_line(0, 0, 100, 50)
+    result = await backend.view_named_save("OVERALL")
+    assert result["ok"] and result["replaced"] is False
+    assert result["center"] == [50.0, 25.0]
+    # extents 100 x 50 at the *Active VPORT's default aspect 1.34: the width
+    # is the binding side, so height = 100 / 1.34
+    assert result["height"] == pytest.approx(100.0 / 1.34)
+    assert result["width"] == pytest.approx(100.0)
+    view = backend._doc.views.get("OVERALL")
+    assert tuple(view.dxf.center)[:2] == (50.0, 25.0)
+
+
+async def test_view_on_an_empty_drawing_needs_an_explicit_window(backend):
+    with pytest.raises(ValueError, match="no extents"):
+        await backend.view_named_save("EMPTY")
+    assert "EMPTY" not in backend._doc.views
+    result = await backend.view_named_save("EMPTY", center=[0, 0], height=10)
+    assert result["center"] == [0.0, 0.0] and result["height"] == 10.0
+    assert result["width"] == pytest.approx(13.4)
+
+
+async def test_view_replace_restore_and_list(backend):
+    await backend.view_named_save("V", center=[1, 2], height=10, width=15)
+    again = await backend.view_named_save("v", center=[5, 5], height=20)
+    assert again["replaced"] is True and again["name"] == "V"
+    assert len(list(backend._doc.views)) == 1
+    restored = await backend.view_named_restore("v")
+    assert restored == {
+        "ok": True,
+        "name": "V",
+        "center": [5.0, 5.0],
+        "height": 20.0,
+        "width": pytest.approx(26.8),
+        "applied": "header_only",
+        "store": "vport_active",
+        "backend": "ezdxf",
+    }
+    (vport,) = backend._doc.viewports.get("*Active")
+    assert tuple(vport.dxf.center)[:2] == (5.0, 5.0) and vport.dxf.height == 20.0
+    assert await backend.view_named_list() == [
+        {"name": "V", "center": [5.0, 5.0], "height": 20.0, "width": pytest.approx(26.8)}
+    ]
+    with pytest.raises(ValueError, match="no named view 'NOPE'"):
+        await backend.view_named_restore("NOPE")
+    with pytest.raises(ValueError, match="height must be > 0"):
+        await backend.view_named_save("BAD", center=[0, 0], height=0)
+    assert "BAD" not in backend._doc.views
+
+
+# ── headless: UCS ───────────────────────────────────────────────────────────
+
+
+async def test_ucs_set_stores_the_entry_and_makes_it_current(backend):
+    result = await backend.ucs_set("FRONT", [10, 10, 0], [0, 1, 0], [-1, 0, 0])
+    assert result == {
+        "ok": True,
+        "name": "FRONT",
+        "origin": [10.0, 10.0, 0.0],
+        "x_axis": [0.0, 1.0, 0.0],
+        "y_axis": [-1.0, 0.0, 0.0],
+        "replaced": False,
+        "current": True,
+        "backend": "ezdxf",
+    }
+    header = backend._doc.header
+    assert header["$UCSNAME"] == "FRONT" and tuple(header["$UCSORG"]) == (10.0, 10.0, 0.0)
+    assert tuple(header["$UCSXDIR"]) == (0.0, 1.0, 0.0)
+    rows = await backend.ucs_list()
+    assert rows[0] == {
+        "name": "world",
+        "origin": [0.0, 0.0, 0.0],
+        "x_axis": [1.0, 0.0, 0.0],
+        "y_axis": [0.0, 1.0, 0.0],
+        "current": False,
+    }
+    assert rows[1]["name"] == "FRONT" and rows[1]["current"] is True
+
+
+async def test_ucs_non_orthogonal_is_refused_before_any_write(backend):
+    with pytest.raises(ValueError, match="measured 60"):
+        await backend.ucs_set("SKEW", [0, 0, 0], [1, 0, 0], [0.5, 0.8660254, 0])
+    assert "SKEW" not in backend._doc.ucs and backend._doc.header["$UCSNAME"] == ""
+
+
+async def test_ucs_restore_world_and_named(backend):
+    await backend.ucs_set("FRONT", [10, 10, 0], [0, 1, 0], [-1, 0, 0])
+    world = await backend.ucs_restore("world")
+    assert world["name"] == "world" and backend._doc.header["$UCSNAME"] == ""
+    assert tuple(backend._doc.header["$UCSXDIR"]) == (1.0, 0.0, 0.0)
+    assert (await backend.ucs_list())[0]["current"] is True
+    named = await backend.ucs_restore("front")
+    assert named["name"] == "FRONT" and backend._doc.header["$UCSNAME"] == "FRONT"
+    with pytest.raises(ValueError, match="no UCS named 'NOPE'"):
+        await backend.ucs_restore("NOPE")
+    with pytest.raises(ValueError, match="reserved"):
+        await backend.ucs_set("world", [0, 0, 0], [1, 0, 0], [0, 1, 0])
+
+
+async def test_ucs_replace_keeps_one_entry(backend):
+    await backend.ucs_set("A", [0, 0, 0], [1, 0, 0], [0, 1, 0])
+    again = await backend.ucs_set("a", [1, 1, 0], [1, 0, 0], [0, 1, 0])
+    assert again["replaced"] is True and again["name"] == "A"
+    assert len(list(backend._doc.ucs)) == 1
+
+
+# ── live engine, against a fake ActiveX surface ──────────────────────────────
+
+
+class _FakeView:
+    def __init__(self, name):
+        self.Name = name
+        self.Center = (0.0, 0.0)
+        self.Height = 100.0
+        self.Width = 150.0
+
+
+class _FakeViews:
+    def __init__(self):
+        self.views: list[_FakeView] = []
+        self.calls: list[tuple[str, tuple]] = []
+
+    @property
+    def Count(self):
+        return len(self.views)
+
+    def Item(self, key):
+        if isinstance(key, int):
+            return self.views[key]
+        for v in self.views:
+            if v.Name.lower() == key.lower():
+                return v
+        raise RuntimeError(f"no view {key}")
+
+    def Add(self, name):
+        self.calls.append(("Add", (name,)))
+        v = _FakeView(name)
+        self.views.append(v)
+        return v
+
+
+class _FakeUcs:
+    def __init__(self, name, origin, xv, yv):
+        self.Name = name
+        self.Origin = origin
+        self.XVector = xv
+        self.YVector = yv
+
+
+class _FakeUcsCollection:
+    def __init__(self):
+        self.items: list[_FakeUcs] = []
+        self.calls: list[tuple[str, tuple]] = []
+
+    @property
+    def Count(self):
+        return len(self.items)
+
+    def Item(self, key):
+        if isinstance(key, int):
+            return self.items[key]
+        for u in self.items:
+            if u.Name.lower() == key.lower():
+                return u
+        raise RuntimeError(f"no ucs {key}")
+
+    def Add(self, origin, x_point, y_point, name):
+        self.calls.append(("Add", (origin, x_point, y_point, name)))
+        # ActiveX stores unit vectors derived from the two points.
+        xv = tuple(p - o for p, o in zip(x_point, origin, strict=True))
+        yv = tuple(p - o for p, o in zip(y_point, origin, strict=True))
+        u = _FakeUcs(name, origin, xv, yv)
+        self.items.append(u)
+        return u
+
+
+class _FakeDocument:
+    def __init__(self):
+        self.Views = _FakeViews()
+        self.UserCoordinateSystems = _FakeUcsCollection()
+        self._viewport = types.SimpleNamespace(Center=(30.0, 40.0), Height=100.0, Width=150.0)
+        self.viewport_sets = 0
+        self.ActiveUCS = None
+        self.commands: list[str] = []
+
+    @property
+    def ActiveViewport(self):
+        return self._viewport
+
+    @ActiveViewport.setter
+    def ActiveViewport(self, value):
+        self._viewport = value
+        self.viewport_sets += 1
+
+    def SendCommand(self, macro):
+        self.commands.append(macro)
+
+
+@pytest.fixture
+def com_backend(monkeypatch):
+    pytest.importorskip("win32com.client", reason="pywin32 not installed")
+    from backends import com_backend as module
+
+    document = _FakeDocument()
+    variables = {"CMDACTIVE": 0, "UCSNAME": ""}
+    app = types.SimpleNamespace(GetVariable=lambda name: variables[name])
+    monkeypatch.setattr(module, "_acad_doc", lambda: document)
+    monkeypatch.setattr(module, "_acad_app", lambda: app)
+    monkeypatch.setattr(module, "_regen", lambda: None)
+    monkeypatch.setattr(module, "_apoint", lambda x, y, z=0.0: (float(x), float(y), float(z)))
+    monkeypatch.setattr(module, "_av", lambda values: tuple(float(v) for v in values))
+    backend = module.ComBackend()
+
+    async def _run_inline(func, *args, **kwargs):
+        return func(*args, **kwargs)
+
+    monkeypatch.setattr(backend, "_run", _run_inline)
+    return backend, document, variables
+
+
+async def test_com_view_save_defaults_to_the_active_viewport(com_backend):
+    backend, document, _ = com_backend
+    result = await backend.view_named_save("HOME")
+    assert document.Views.calls == [("Add", ("HOME",))]
+    (view,) = document.Views.views
+    assert view.Center == (30.0, 40.0) and view.Height == 100.0 and view.Width == 150.0
+    assert result["center"] == [30.0, 40.0] and result["replaced"] is False
+    again = await backend.view_named_save("home", center=[1, 2], height=10)
+    assert again["replaced"] is True and len(document.Views.views) == 1
+    assert view.Center == (1.0, 2.0) and view.Height == 10.0 and view.Width == 15.0
+
+
+async def test_com_view_restore_sets_the_active_viewport(com_backend):
+    backend, document, _ = com_backend
+    await backend.view_named_save("HOME", center=[5, 6], height=20, width=30)
+    result = await backend.view_named_restore("HOME")
+    assert result["applied"] == "active_viewport"
+    assert document.ActiveViewport.Center == (5.0, 6.0)
+    assert document.ActiveViewport.Height == 20.0 and document.ActiveViewport.Width == 30.0
+    assert document.viewport_sets == 1, "ActiveX applies a viewport change only on re-assignment"
+    assert await backend.view_named_list() == [
+        {"name": "HOME", "center": [5.0, 6.0], "height": 20.0, "width": 30.0}
+    ]
+
+
+async def test_com_ucs_add_uses_points_on_the_axes_not_vectors(com_backend):
+    backend, document, variables = com_backend
+    result = await backend.ucs_set("FRONT", [10, 10, 0], [0, 5, 0], [-1, 0, 0])
+    assert document.UserCoordinateSystems.calls == [
+        ("Add", ((10.0, 10.0, 0.0), (10.0, 11.0, 0.0), (9.0, 10.0, 0.0), "FRONT"))
+    ]
+    assert document.ActiveUCS is document.UserCoordinateSystems.items[0]
+    assert result["x_axis"] == [0.0, 1.0, 0.0] and result["current"] is True
+    variables["UCSNAME"] = "FRONT"
+    rows = await backend.ucs_list()
+    assert rows[0]["name"] == "world" and rows[0]["current"] is False
+    assert rows[1] == {
+        "name": "FRONT",
+        "origin": [10.0, 10.0, 0.0],
+        "x_axis": [0.0, 1.0, 0.0],
+        "y_axis": [-1.0, 0.0, 0.0],
+        "current": True,
+    }
+
+
+async def test_com_ucs_restore_world_sends_the_ucs_command_when_idle(com_backend):
+    backend, document, variables = com_backend
+    result = await backend.ucs_restore("world")
+    assert document.commands == ["_.UCS _W\n"] and result["name"] == "world"
+    variables["CMDACTIVE"] = 1
+    with pytest.raises(RuntimeError, match="CMDACTIVE"):
+        await backend.ucs_restore("world")
+    assert len(document.commands) == 1
+
+
+async def test_com_ucs_refuses_before_activex(com_backend):
+    backend, document, _ = com_backend
+    with pytest.raises(ValueError, match="measured"):
+        await backend.ucs_set("SKEW", [0, 0, 0], [1, 0, 0], [1, 1, 0])
+    assert document.UserCoordinateSystems.calls == []