fix(task-10): $DIMBLK header carries the canonical arrowhead name; MLeaderStyle is authored on COM through the ACAD_MLEADERSTYLE dictionary

Two review findings, both root causes.

1. `_sync_header_to_dimstyle` copied the DIMSTYLE entry's ezdxf-internal
   arrowhead spelling (OBLIQUE) into the DXF-facing $DIMBLK/$DIMBLK1/$DIMBLK2
   header, so the saved file named a block it did not hold (the blocks are
   _OBLIQUE / _DOT) and `system_get_variable("DIMBLK")` answered "OBLIQUE"
   headlessly against "_OBLIQUE" on COM and in the same engine's own
   `dimstyle_list` row. The header write now goes through
   `reported_arrowhead` — the same read-side rule `_dimstyle_value` applies.
   Pinned by header, `system_get_variable`, save/reopen (`ezdxf.readfile`
   header equals the block the file holds) and the Restore-to-Standard
   empty-string case in `test_builtin_arrowheads_render_save_and_report_one_spelling`.

2. The `mleaderstyle` capability refusal rested on a false engine boundary.
   acax25enu.tlb (AutoCAD 2026) exposes IAcadMLeaderStyle with Name,
   ArrowSize, LandingGap, TextHeight, TextStyle, ... — exactly what
   `Dictionaries.Item("ACAD_MLEADERSTYLE").Item(i)` returns — and
   IAcadDictionary.AddObject(keyword, "AcDbMLeaderStyle") creates one.
   COM `mleaderstyle_list` now reads the four values off those objects
   (`values_available: True`); COM `mleaderstyle_create` validates every value
   (`validate_mleaderstyle`, shared with ezdxf), checks the clash and the text
   style before AddObject, then writes the four properties. The contract
   method is `@abstractmethod` again, the key is gone from both capability
   maps, the fake ActiveX surface models the real call shape, and the spec
   (§4.2, §8.1, §9) states the ActiveX route.

Live AutoCAD was not running on this machine (GetActiveObject: operation
unavailable; no acad.exe), so the COM route is type-library-verified and
fake-tested, not executed live — scripts/smoke_settings_com.py (Task 24)
owns that.

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

backends/com_backend.py

@@ -341,6 +341,39 @@ def _com_font_on_support_path(font_file: str) -> bool:
     return any((Path(folder) / font_file).is_file() for folder in support.split(";") if folder)
 
 
+_MLEADERSTYLE_DICTIONARY = "ACAD_MLEADERSTYLE"
+_MLEADERSTYLE_CLASS = "AcDbMLeaderStyle"
+
+
+def _com_mleaderstyle_dictionary(doc, *, create: bool = False):
+    """The ``ACAD_MLEADERSTYLE`` dictionary, or None when the drawing has none.
+
+    ActiveX exposes no ``MLeaderStyles`` *collection*, but the dictionary's
+    items are full ``IAcadMLeaderStyle`` objects (acax25enu.tlb: ``Name``,
+    ``ArrowSize``, ``LandingGap``, ``TextHeight``, ``TextStyle``, ...), and
+    ``IAcadDictionary.AddObject(keyword, "AcDbMLeaderStyle")`` — the
+    documented VBA route — creates one. Every drawing AutoCAD makes carries
+    the dictionary; ``create`` adds it to a foreign file that does not. The
+    route is verified against the AutoCAD 2026 type library and fake-tested;
+    its live execution is scripts/smoke_settings_com.py's job.
+    """
+    try:
+        return doc.Dictionaries.Item(_MLEADERSTYLE_DICTIONARY)
+    except Exception:
+        if not create:
+            return None
+    return doc.Dictionaries.Add(_MLEADERSTYLE_DICTIONARY)
+
+
+def _com_mleaderstyle_rows(dictionary) -> list[tuple[str, Any]]:
+    """``(name, AcadMLeaderStyle)`` for every item, named by the dictionary key."""
+    rows = []
+    for index in range(dictionary.Count):
+        style = dictionary.Item(index)
+        rows.append((str(dictionary.GetName(style)), style))
+    return rows
+
+
 def _ensure_com_textstyle(doc, name: str, *, refusal_key: str) -> tuple[str, bool]:
     """``(name as AutoCAD spells it, created)``; a preset is created, anything else missing is refused."""
     from engineering.standards.textstyles import TEXT_PRESETS
@@ -923,13 +956,6 @@ class ComBackend(AutoCADBackend):
                 "viewport_render": FeatureCapability(True, "native"),
                 "solid_3d": _solid_3d_capability(),
                 "lisp": FeatureCapability(True, "sanitized"),
-                "mleaderstyle": FeatureCapability(
-                    False,
-                    reason=(
-                        "no_activex_mleaderstyle_collection;"
-                        "use_leader_create_mleader_per_leader_parameters"
-                    ),
-                ),
             },
         )
 
@@ -4420,21 +4446,19 @@ class ComBackend(AutoCADBackend):
     async def mleaderstyle_list(self) -> list[dict]:
         def _sync():
             doc = _acad_doc()
-            try:
-                dictionary = doc.Dictionaries.Item("ACAD_MLEADERSTYLE")
-            except Exception:
+            dictionary = _com_mleaderstyle_dictionary(doc)
+            if dictionary is None:
                 return []
             rows = []
-            for index in range(dictionary.Count):
+            for name, style in _com_mleaderstyle_rows(dictionary):
                 rows.append(
                     {
-                        "name": str(dictionary.GetName(dictionary.Item(index))),
-                        # ActiveX exposes no MLeaderStyle object: names only.
-                        "arrow_size": None,
-                        "landing_gap": None,
-                        "text_style": None,
-                        "text_height": None,
-                        "values_available": False,
+                        "name": name,
+                        "arrow_size": float(style.ArrowSize),
+                        "landing_gap": float(style.LandingGap),
+                        "text_style": str(style.TextStyle),
+                        "text_height": float(style.TextHeight),
+                        "values_available": True,
                     }
                 )
             rows.sort(key=lambda row: row["name"].lower())
@@ -4442,6 +4466,40 @@ class ComBackend(AutoCADBackend):
 
         return await self._run(_sync)
 
+    async def mleaderstyle_create(self, name: str, values: dict) -> dict:
+        from engineering.standards.mleaderstyles import validate_mleaderstyle
+
+        clean = sanitize_symbol_name(name, kind="mleaderstyle")
+        typed = validate_mleaderstyle(values)
+
+        def _sync():
+            doc = _acad_doc()
+            dictionary = _com_mleaderstyle_dictionary(doc, create=True)
+            wanted = clean.lower()
+            if any(
+                existing.lower() == wanted for existing, _ in _com_mleaderstyle_rows(dictionary)
+            ):
+                raise ValueError(f"mleaderstyle_create: leader style {clean!r} already exists")
+            # The text style must exist before TextStyle can name it — and a
+            # name that is neither present nor a preset is refused here,
+            # before AddObject, so a refusal leaves no half-made style behind.
+            text_style_name, textstyle_created = _ensure_com_textstyle(
+                doc, typed["text_style"], refusal_key="text_style"
+            )
+            style = dictionary.AddObject(clean, _MLEADERSTYLE_CLASS)
+            style.ArrowSize = typed["arrow_size"]
+            style.LandingGap = typed["landing_gap"]
+            style.TextHeight = typed["text_height"]
+            style.TextStyle = text_style_name
+            return {
+                "ok": True,
+                "name": clean,
+                "values": {**typed, "text_style": text_style_name},
+                "textstyle_created": textstyle_created,
+            }
+
+        return await self._run(_sync)
+
     # ── corner ops ──────────────────────────────────────────────────────────
 
     @staticmethod

backends/contracts/styles.py

@@ -14,8 +14,6 @@ from __future__ import annotations
 
 from abc import ABC, abstractmethod
 
-from backends.capability import capability
-
 
 class StylesContract(ABC):
     @abstractmethod
@@ -115,29 +113,24 @@ class StylesContract(ABC):
     async def mleaderstyle_list(self) -> list[dict]:
         """``[{name, arrow_size, landing_gap, text_style, text_height, values_available}]``.
 
-        Headless the values are read from the MLEADERSTYLE object (schema
-        defaults for an unset field). ActiveX exposes no MLeaderStyle object,
-        so the live engine reads the *names* from the ``ACAD_MLEADERSTYLE``
-        dictionary and reports the four values ``None`` with
-        ``values_available: False``.
+        Both engines report the four values (``values_available: True``).
+        Headless they are read from the MLEADERSTYLE object (schema defaults
+        for an unset field); live from the ``AcadMLeaderStyle`` objects the
+        ``ACAD_MLEADERSTYLE`` dictionary holds (``ArrowSize`` / ``LandingGap``
+        / ``TextHeight`` in drawing units, ``TextStyle`` a name) — ActiveX
+        exposes no *collection* property for them, but the dictionary items
+        are full ``IAcadMLeaderStyle`` objects.
         """
         ...
 
-    # B027 (empty method, no @abstractmethod) is what this pattern looks like
-    # from the outside: the decorator replaces the `...` body with the refusing
-    # default, so the source really is empty on purpose.
-    @capability(  # noqa: B027
-        "mleaderstyle",
-        reason=(
-            "ActiveX exposes no MLeaderStyle collection; use leader_create_mleader's "
-            "per-leader parameters (arrow size, landing, text height) or the headless "
-            "backend (AUTOCAD_MCP_BACKEND=ezdxf)"
-        ),
-    )
+    @abstractmethod
     async def mleaderstyle_create(self, name: str, values: dict) -> dict:
         """Create a multileader style from a resolved ``values`` dict
         (``engineering.standards.mleaderstyles.resolve_mleaderstyle``).
-        ezdxf only. Returns ``{ok, name, values, textstyle_created}``; the
-        text style follows the ``dimstyle_create`` rule (exists or preset,
-        else refused by name); a clash is refused."""
+        Both engines: ezdxf on ``doc.mleader_styles``; live through
+        ``Dictionaries.Item("ACAD_MLEADERSTYLE").AddObject(name,
+        "AcDbMLeaderStyle")`` and the object's property writes. Returns
+        ``{ok, name, values, textstyle_created}``; the text style follows the
+        ``dimstyle_create`` rule (exists or preset, else refused by name); a
+        clash is refused — before anything is written."""
         ...

backends/ezdxf_backend.py

@@ -830,8 +830,18 @@ def _sync_header_to_dimstyle(doc, style) -> None:
     `Standard` reproduces the header `drawing_new` made. `DIMTXSTY` has no
     schema default; AutoCAD reads ``Standard`` for it, as `_dimstyle_value`
     reports.
+
+    The arrowheads cross a vocabulary boundary here. The DIMSTYLE entry holds
+    ezdxf's writer spelling (``OBLIQUE``, see `_write_dimstyle_values`); the
+    ``$DIMBLK`` / ``$DIMBLK1`` / ``$DIMBLK2`` header variables are DXF-facing
+    and spell a built-in with its underscore (``_OBLIQUE``, what a live seat
+    stores and what `system_get_variable("DIMBLK")` returns on COM). Copied
+    raw, the saved file carried ``$DIMBLK "OBLIQUE"`` next to blocks named
+    ``_OBLIQUE`` — a current-override naming a block that does not exist —
+    and the two engines answered the same read two ways. `reported_arrowhead`
+    is the same read-side rule `_dimstyle_value` applies.
     """
-    from engineering.standards.dimstyles import DIM_VARIABLE_WHITELIST
+    from engineering.standards.dimstyles import DIM_VARIABLE_WHITELIST, reported_arrowhead
 
     for var in sorted(DIM_VARIABLE_WHITELIST):
         attr = var.lower()
@@ -840,6 +850,8 @@ def _sync_header_to_dimstyle(doc, style) -> None:
             value = _dimstyle_schema_default(var)
         if value is None and var == "DIMTXSTY":
             value = "Standard"
+        if var in _ARROWHEAD_VARS:
+            value = reported_arrowhead(value)
         key = f"${var}"
         if value is None:
             try:
@@ -1342,7 +1354,6 @@ class EzdxfBackend(AutoCADBackend):
                     False, reason="acis_generation_requires_live_autocad"
                 ),
                 "lisp": FeatureCapability(False, reason="live_com_only"),
-                "mleaderstyle": FeatureCapability(True, "native"),
             },
         )
 
@@ -6079,38 +6090,29 @@ class EzdxfBackend(AutoCADBackend):
         return await self._async(_sync)
 
     async def mleaderstyle_create(self, name: str, values: dict) -> dict:
-        from engineering.standards.mleaderstyles import MLEADER_KEYS
+        from engineering.standards.mleaderstyles import validate_mleaderstyle
         from security import sanitize_symbol_name
 
         clean = sanitize_symbol_name(name, kind="mleaderstyle")
-        missing = [key for key in MLEADER_KEYS if key not in values]
-        if missing:
-            raise ValueError(
-                f"mleaderstyle_create: values is missing {missing}; resolve a preset first"
-            )
+        typed = validate_mleaderstyle(values)
 
         def _sync():
             doc = self._require_doc()
             if doc.mleader_styles.has_entry(clean):
                 raise ValueError(f"mleaderstyle_create: leader style {clean!r} already exists")
             text_style_name, textstyle_created = _ensure_textstyle(
-                doc, str(values["text_style"]), refusal_key="text_style"
+                doc, typed["text_style"], refusal_key="text_style"
             )
             style = doc.mleader_styles.new(clean)
-            style.dxf.arrow_head_size = float(values["arrow_size"])
-            style.dxf.landing_gap_size = float(values["landing_gap"])
-            style.dxf.char_height = float(values["text_height"])
+            style.dxf.arrow_head_size = typed["arrow_size"]
+            style.dxf.landing_gap_size = typed["landing_gap"]
+            style.dxf.char_height = typed["text_height"]
             style.dxf.text_style_handle = doc.styles.get(text_style_name).dxf.handle
             self._mark_dirty()
             return {
                 "ok": True,
                 "name": clean,
-                "values": {
-                    "arrow_size": float(values["arrow_size"]),
-                    "landing_gap": float(values["landing_gap"]),
-                    "text_style": text_style_name,
-                    "text_height": float(values["text_height"]),
-                },
+                "values": {**typed, "text_style": text_style_name},
                 "textstyle_created": textstyle_created,
             }
 

docs/superpowers/specs/2026-09-16-v1.6-settings-design.md

@@ -118,7 +118,7 @@ name.
 - `dimstyle_modify(name, overrides)` — `changed` reports only variables that actually moved (the `hatch_edit` rule). Dimensions already using the style are listed in `dimensions_using_style` with `rerender_required: true` on the headless engine: AutoCAD re-renders them on the next regen, but a headless DIMENSION carries its rendered block, so the drawing shows the old style until the dimension is redrawn — stated rather than silent.
 - `dimstyle_set_current(name)` — `$DIMSTYLE`; the dimension tools then use it (the existing per-dimension override path stays as is).
 - `textstyle_list()`, `textstyle_create(name, font: "isocp.shx"|"isocpeur.ttf"|"arial.ttf"|"romans.shx"|<file>, height=0.0, width_factor=1.0, oblique_deg=0.0, set_current=False)`, `textstyle_set_current(name)` — `$TEXTSTYLE`; a font file that is neither a bundled preset nor present in the engine's font path is written but reported `font_resolved: false` (AutoCAD substitutes at open; the headless renderer falls back), never refused, because DXF only stores the name.
-- `mleaderstyle_list()`, `mleaderstyle_create(name, preset: "iso"|"ansi", overrides)` — arrow size, landing gap, text style, text height on ezdxf's `doc.mleader_styles`. ActiveX exposes no MLeaderStyle collection, so the COM engine refuses both with `capability: "mleaderstyle"` (the reason names `leader_create_mleader`'s existing per-leader parameters as the route); `mleaderstyle_list` on COM still reads the names from the `ACAD_MLEADERSTYLE` dictionary.
+- `mleaderstyle_list()`, `mleaderstyle_create(name, preset: "iso"|"ansi", overrides)` — arrow size, landing gap, text style, text height, both engines: ezdxf on `doc.mleader_styles`; COM through the `ACAD_MLEADERSTYLE` dictionary, whose items are `IAcadMLeaderStyle` objects (`ArrowSize` / `LandingGap` / `TextHeight` in drawing units, `TextStyle` a name — verified against the AutoCAD 2026 type library), created with `Dictionaries.Item("ACAD_MLEADERSTYLE").AddObject(name, "AcDbMLeaderStyle")` followed by the property writes. ActiveX has no `MLeaderStyles` *collection* property, which is not an engine boundary — no `mleaderstyle` capability key exists.
 - `drawing_apply_standard(standard: "iso"|"ansi", layers: bool = True, units: bool = True)` — one call: the dimstyle preset (created and set current), its text style, `drawing_settings` (units mm, decimal linear and angular units, LTSCALE 1, DIMSCALE 1; the decimal separator comes from the preset) and, with `layers`, the `mech` layer set for both standards (ANSI layer naming is company-specific; the set reuses the mech names with ISO 128 lineweights — only styles and the separator differ between the two). Returns, per item, whether it was created or was already present.
 
 ## 5. Settings (SECTION 20 shares these; 3 tools + facade growth)
@@ -187,9 +187,10 @@ A state is the layer table snapshot `{layer: {on, frozen, locked, color, linetyp
 
 ### 8.1 Capability keys (added to **both** maps)
 
-`mleaderstyle` (COM false), `dwgprops` (ezdxf false: summary fields), `dwt_write`
-(ezdxf false), `live_application`, `preferences`, `interactive_prompt` (ezdxf
-false). `tests/test_capability_contract.py` enforces both maps.
+`dwgprops` (ezdxf false: summary fields), `dwt_write` (ezdxf false),
+`live_application`, `preferences`, `interactive_prompt` (ezdxf false).
+`tests/test_capability_contract.py` enforces both maps. (`mleaderstyle` was
+listed here as COM false; the ActiveX route exists — §4.2 — so there is no key.)
 
 ### 8.2 Packs, profiles, discovery
 
@@ -219,7 +220,9 @@ shop-floor synonyms; the discovery golden set gains ≥ 10 queries for them
   (A0 841×1189 … A4 210×297; ANSI A 216×279 … E 864×1118), every catalog
   sysvar has type+meaning+engines.
 - Dual-engine tests for every tool (ezdxf real; COM fake-ActiveX asserting call
-  shapes: `DimStyles.Add`, `TextStyles.Add`, `Layout.ConfigName/…`,
+  shapes: `DimStyles.Add`, `TextStyles.Add`,
+  `Dictionaries.Item("ACAD_MLEADERSTYLE").AddObject(name, "AcDbMLeaderStyle")`,
+  `Layout.ConfigName/…`,
   `Documents.Item().Activate`, `Dictionaries.Add`+`AddXRecord`, `Views.Add`,
   `UserCoordinateSystems.Add`, `Preferences.OpenSave.*`, `SummaryInfo.*`,
   `Utility.GetPoint`).

engineering/standards/__init__.py

@@ -23,7 +23,11 @@ from engineering.standards.dimstyles import (
     resolve_dimstyle,
     validate_overrides,
 )
-from engineering.standards.mleaderstyles import MLEADER_PRESETS, resolve_mleaderstyle
+from engineering.standards.mleaderstyles import (
+    MLEADER_PRESETS,
+    resolve_mleaderstyle,
+    validate_mleaderstyle,
+)
 from engineering.standards.textstyles import TEXT_PRESETS, resolve_font, validate_textstyle
 
 __all__ = [
@@ -42,6 +46,7 @@ __all__ = [
     "resolve_dimstyle",
     "resolve_font",
     "resolve_mleaderstyle",
+    "validate_mleaderstyle",
     "validate_overrides",
     "validate_textstyle",
 ]

engineering/standards/mleaderstyles.py

@@ -2,8 +2,10 @@
 
 Sized to match the dimension presets they sit beside (ISO-25: 2.5 mm arrows
 and lettering; ANSI: 3 mm), so a leader note and a dimension on the same
-sheet read at one size. Only ezdxf can author an MLEADERSTYLE object;
-ActiveX exposes no collection for it (see ``backends/contracts/styles.py``).
+sheet read at one size. Both engines author the style: ezdxf on
+``doc.mleader_styles``, ActiveX through the ``ACAD_MLEADERSTYLE`` dictionary's
+``AddObject(name, "AcDbMLeaderStyle")`` and the ``IAcadMLeaderStyle``
+properties (see ``backends/contracts/styles.py``).
 """
 
 from __future__ import annotations
@@ -13,7 +15,7 @@ from typing import Any
 
 from engineering.standards.names import check_name
 
-__all__ = ["MLEADER_KEYS", "MLEADER_PRESETS", "resolve_mleaderstyle"]
+__all__ = ["MLEADER_KEYS", "MLEADER_PRESETS", "resolve_mleaderstyle", "validate_mleaderstyle"]
 
 MLEADER_PRESETS: dict[str, dict[str, Any]] = {
     "iso": {"arrow_size": 2.5, "landing_gap": 1.0, "text_style": "ISOCP", "text_height": 2.5},
@@ -57,3 +59,27 @@ def resolve_mleaderstyle(preset: str, overrides: dict | None = None) -> dict[str
         else:
             values[name] = _positive(name, value)
     return values
+
+
+def validate_mleaderstyle(values: Any) -> dict[str, Any]:
+    """The four ``MLEADER_KEYS`` of ``values``, typed, or a refusal naming the key.
+
+    What both engines' ``mleaderstyle_create`` run before touching a table:
+    a missing key is ``ValueError`` (``resolve a preset first``), and each
+    value is checked exactly as :func:`resolve_mleaderstyle` checks an
+    override — so a hand-built dict is held to the preset's rules too.
+    Unknown keys are ignored: the row shape is the contract, not the input.
+    """
+    if not isinstance(values, dict):
+        raise TypeError(f"values: expected a mapping, got {type(values).__name__}")
+    missing = [key for key in MLEADER_KEYS if key not in values]
+    if missing:
+        raise ValueError(
+            f"mleaderstyle_create: values is missing {missing}; resolve a preset first"
+        )
+    return {
+        "arrow_size": _positive("arrow_size", values["arrow_size"]),
+        "landing_gap": _positive("landing_gap", values["landing_gap"], allow_zero=True),
+        "text_style": check_name("text_style", values["text_style"], what="text style name"),
+        "text_height": _positive("text_height", values["text_height"]),
+    }

tests/test_standards_presets.py

@@ -30,6 +30,7 @@ from engineering.standards.mleaderstyles import (
     MLEADER_KEYS,
     MLEADER_PRESETS,
     resolve_mleaderstyle,
+    validate_mleaderstyle,
 )
 from engineering.standards.textstyles import TEXT_PRESETS, resolve_font, validate_textstyle
 
@@ -564,3 +565,28 @@ def test_resolve_mleaderstyle_applies_overrides():
 def test_resolve_mleaderstyle_refuses_by_name(preset, overrides, exc, fragment):
     with pytest.raises(exc, match=fragment):
         resolve_mleaderstyle(preset, overrides)
+
+
+def test_validate_mleaderstyle_types_the_four_keys_and_refuses_by_name():
+    """What both engines' ``mleaderstyle_create`` run before any write: a
+    hand-built dict is held to the same rules as a preset override."""
+    assert validate_mleaderstyle(resolve_mleaderstyle("iso")) == MLEADER_PRESETS["iso"]
+    typed = validate_mleaderstyle(
+        {"arrow_size": 3, "landing_gap": 0, "text_style": " arial ", "text_height": 2, "extra": 1}
+    )
+    assert typed == {
+        "arrow_size": 3.0,
+        "landing_gap": 0.0,
+        "text_style": "arial",
+        "text_height": 2.0,
+    }
+    with pytest.raises(ValueError, match=r"missing \['landing_gap', 'text_style', 'text_height'\]"):
+        validate_mleaderstyle({"arrow_size": 2.5})
+    with pytest.raises(ValueError, match="arrow_size"):
+        validate_mleaderstyle({**MLEADER_PRESETS["iso"], "arrow_size": 0})
+    with pytest.raises(ValueError, match="text_style"):
+        validate_mleaderstyle({**MLEADER_PRESETS["iso"], "text_style": "a|b"})
+    with pytest.raises(TypeError, match="text_height"):
+        validate_mleaderstyle({**MLEADER_PRESETS["iso"], "text_height": "2.5"})
+    with pytest.raises(TypeError, match="values"):
+        validate_mleaderstyle(["arrow_size"])

tests/test_styles.py

@@ -16,7 +16,6 @@ import ezdxf
 import pytest
 
 import config
-from backends.base import UnsupportedCapabilityError
 from backends.capability import is_capability_default
 from backends.ezdxf_backend import _current_dimstyle_name, _current_textstyle_name
 from engineering.standards.dimstyles import PRESET_VARIABLES, resolve_dimstyle
@@ -162,13 +161,31 @@ async def test_builtin_arrowheads_render_save_and_report_one_spelling(backend, t
     )
     again = await backend.dimstyle_modify("ISO-25", {"DIMBLK": "OBLIQUE", "DIMBLK1": "_dot"})
     assert again["changed"] == {}, "re-setting a value to itself is not a change (spec §8.3)"
+    # The style is current, so Restore loaded it into the $DIM* header. The
+    # header is DXF-facing: a built-in is spelled with its underscore there
+    # (what a live seat stores and what COM's system_get_variable returns),
+    # never ezdxf's writer spelling the DIMSTYLE entry holds.
+    header = backend._doc.header
+    assert (header["$DIMBLK"], header["$DIMBLK1"], header["$DIMBLK2"]) == ("_OBLIQUE", "_DOT", "")
+    assert await backend.system_get_variable("DIMBLK") == "_OBLIQUE", "the same answer as COM"
     path = str(tmp_path / "arrows.dxf")
     await backend.drawing_save_as(path)
+    saved = ezdxf.readfile(path)
+    assert saved.header["$DIMBLK"] == "_OBLIQUE" and saved.header["$DIMBLK1"] == "_DOT", (
+        "the file names the block it actually holds, not a block that does not exist"
+    )
+    assert "_OBLIQUE" in saved.blocks and "_DOT" in saved.blocks
     await backend.drawing_open(path)
     rows = {r["name"]: r for r in await backend.dimstyle_list()}
     assert rows["ISO-25"]["values"]["DIMBLK"] == "_OBLIQUE", "reloaded, the same spelling"
+    assert await backend.system_get_variable("DIMBLK") == "_OBLIQUE"
     reopened = await backend.dimstyle_modify("ISO-25", {"DIMBLK": "oblique"})
     assert reopened["changed"] == {}
+    await backend.dimstyle_set_current("Standard")
+    header = backend._doc.header  # drawing_open replaced the document
+    assert (header["$DIMBLK"], header["$DIMBLK1"], header["$DIMBLK2"]) == ("", "", ""), (
+        "closed filled is the empty string in the header, as in a fresh drawing"
+    )
 
 
 async def test_user_arrowhead_block_must_exist_before_anything_is_written(backend):
@@ -434,12 +451,20 @@ async def test_mleaderstyle_refusals_write_nothing(backend):
     assert not backend._doc.mleader_styles.has_entry("X")
 
 
-async def test_both_capability_maps_declare_mleaderstyle(backend):
+async def test_mleaderstyle_is_not_a_capability_boundary_on_either_engine(backend):
+    """The v1.6 plan declared `mleaderstyle` COM-unsupported ("ActiveX exposes
+    no MLeaderStyle collection"). The type library says otherwise: the
+    ACAD_MLEADERSTYLE dictionary items are IAcadMLeaderStyle objects and
+    AddObject(name, "AcDbMLeaderStyle") creates one. A refusal resting on a
+    false premise is exactly what CLAUDE.md forbids `@capability` for, so
+    neither map declares the key and neither engine inherits a default."""
     from backends.com_backend import ComBackend
 
-    assert backend.capabilities().to_dict()["features"]["mleaderstyle"]["supported"] is True
-    com = ComBackend().capabilities().to_dict()["features"]["mleaderstyle"]
-    assert com["supported"] is False and "leader_create_mleader" in com["reason"]
+    assert "mleaderstyle" not in backend.capabilities().to_dict()["features"]
+    assert "mleaderstyle" not in ComBackend().capabilities().to_dict()["features"]
+    for engine in (type(backend), ComBackend):
+        assert not is_capability_default(engine, "mleaderstyle_create")
+        assert not is_capability_default(engine, "mleaderstyle_list")
 
 
 # ── live engine, against a fake ActiveX surface ──────────────────────────────
@@ -506,9 +531,32 @@ class _FakeLayouts:
         return self.layouts[index]
 
 
+class _FakeMLeaderStyle:
+    """An AcadMLeaderStyle: the properties acax25enu.tlb's IAcadMLeaderStyle
+    exposes that the backend reads or writes (doubles in drawing units, the
+    text style by name), with AutoCAD's defaults for a fresh style."""
+
+    PROPERTIES = ("ArrowSize", "LandingGap", "TextHeight", "TextStyle")
+
+    def __init__(self, name, calls):
+        self.Name = name
+        self.ObjectName = "AcDbMLeaderStyle"
+        self.ArrowSize, self.LandingGap, self.TextHeight, self.TextStyle = 4.0, 2.0, 4.0, "Standard"
+        self._calls = calls  # last: property writes are recorded from here on
+
+    def __setattr__(self, key, value):
+        if key in self.PROPERTIES and "_calls" in vars(self):
+            self._calls.append(("MLeaderStyle." + key, self.Name, value))
+        super().__setattr__(key, value)
+
+
 class _FakeDictionary:
-    def __init__(self, *names):
-        self.objects = [types.SimpleNamespace(mleader_name=name) for name in names]
+    """The ACAD_MLEADERSTYLE dictionary: Count/Item/GetName over its objects
+    and AddObject(keyword, class_name), the documented VBA route."""
+
+    def __init__(self, calls, *names):
+        self._calls = calls
+        self.objects = [_FakeMLeaderStyle(name, calls) for name in names]
 
     @property
     def Count(self):
@@ -518,7 +566,15 @@ class _FakeDictionary:
         return self.objects[index]
 
     def GetName(self, obj):
-        return obj.mleader_name
+        return obj.Name
+
+    def AddObject(self, keyword, class_name):
+        self._calls.append(("Dictionary.AddObject", keyword, class_name))
+        if class_name != "AcDbMLeaderStyle":
+            raise RuntimeError(f"cannot create {class_name} here")
+        style = _FakeMLeaderStyle(keyword, self._calls)
+        self.objects.append(style)
+        return style
 
 
 class _FakeDictionaries:
@@ -570,7 +626,7 @@ class _FakeDocument:
         )
         self.Layouts = _FakeLayouts(_FakeBlock(dim, line), _FakeBlock(sheet_dim))
         self.Dictionaries = _FakeDictionaries(
-            {"ACAD_MLEADERSTYLE": _FakeDictionary("Standard", "Annotative")}
+            {"ACAD_MLEADERSTYLE": _FakeDictionary(self.calls, "Standard", "Annotative")}
         )
 
     def GetVariable(self, name):
@@ -751,36 +807,74 @@ async def test_com_textstyle_create_sets_font_width_oblique_height(com_backend):
     assert back == {"ok": True, "current": "Standard", "previous": "ISOCP", "changed": True}
 
 
-async def test_com_mleaderstyle_list_reads_the_dictionary_names_only(com_backend):
+async def test_com_mleaderstyle_list_reads_the_values_off_the_dictionary_objects(com_backend):
     backend, document = com_backend
+    dictionary = document.Dictionaries.Item("ACAD_MLEADERSTYLE")
+    dictionary.objects[1].ArrowSize = 3.0
+    dictionary.objects[1].TextStyle = "ISOCP"
+    document.calls.clear()  # fixture setup, not backend calls
     rows = await backend.mleaderstyle_list()
     assert rows == [
         {
             "name": "Annotative",
-            "arrow_size": None,
-            "landing_gap": None,
-            "text_style": None,
-            "text_height": None,
-            "values_available": False,
+            "arrow_size": 3.0,
+            "landing_gap": 2.0,
+            "text_style": "ISOCP",
+            "text_height": 4.0,
+            "values_available": True,
         },
         {
             "name": "Standard",
-            "arrow_size": None,
-            "landing_gap": None,
-            "text_style": None,
-            "text_height": None,
-            "values_available": False,
+            "arrow_size": 4.0,
+            "landing_gap": 2.0,
+            "text_style": "Standard",
+            "text_height": 4.0,
+            "values_available": True,
         },
     ]
+    assert document.calls == [], "a list reads; it writes nothing"
 
 
-async def test_com_mleaderstyle_create_refuses_with_the_capability_key(com_backend):
-    from backends.com_backend import ComBackend
-
+async def test_com_mleaderstyle_create_adds_the_object_then_writes_its_properties(com_backend):
     backend, document = com_backend
-    assert is_capability_default(ComBackend, "mleaderstyle_create")
-    with pytest.raises(UnsupportedCapabilityError) as excinfo:
-        await backend.mleaderstyle_create("ISO", resolve_mleaderstyle("iso", None))
-    assert excinfo.value.capability == "mleaderstyle"
-    assert "leader_create_mleader" in str(excinfo.value)
-    assert document.calls == []
+    result = await backend.mleaderstyle_create("ISO", resolve_mleaderstyle("iso", None))
+    assert result == {
+        "ok": True,
+        "name": "ISO",
+        "values": {
+            "arrow_size": 2.5,
+            "landing_gap": 1.0,
+            "text_style": "ISOCP",
+            "text_height": 2.5,
+        },
+        "textstyle_created": True,
+    }
+    names = [call[0] for call in document.calls]
+    assert names.index("TextStyles.Add") < names.index("Dictionary.AddObject"), (
+        "the text style exists before TextStyle names it"
+    )
+    assert ("Dictionary.AddObject", "ISO", "AcDbMLeaderStyle") in document.calls
+    writes = [call for call in document.calls if call[0].startswith("MLeaderStyle.")]
+    assert writes == [
+        ("MLeaderStyle.ArrowSize", "ISO", 2.5),
+        ("MLeaderStyle.LandingGap", "ISO", 1.0),
+        ("MLeaderStyle.TextHeight", "ISO", 2.5),
+        ("MLeaderStyle.TextStyle", "ISO", "ISOCP"),
+    ]
+    rows = {row["name"]: row for row in await backend.mleaderstyle_list()}
+    assert rows["ISO"] == {**result["values"], "name": "ISO", "values_available": True}
+
+
+async def test_com_mleaderstyle_refusals_write_nothing(com_backend):
+    backend, document = com_backend
+    dictionary = document.Dictionaries.Item("ACAD_MLEADERSTYLE")
+    with pytest.raises(ValueError, match="already exists"):
+        await backend.mleaderstyle_create("standard", resolve_mleaderstyle("iso", None))
+    with pytest.raises(ValueError, match="text_style"):
+        await backend.mleaderstyle_create("X", resolve_mleaderstyle("iso", {"text_style": "NOPE"}))
+    with pytest.raises(ValueError, match="missing"):
+        await backend.mleaderstyle_create("X", {"arrow_size": 2.5})
+    with pytest.raises(ValueError, match="arrow_size"):
+        await backend.mleaderstyle_create("X", {**resolve_mleaderstyle("iso"), "arrow_size": 0})
+    assert document.calls == [], "nothing reached ActiveX"
+    assert [obj.Name for obj in dictionary.objects] == ["Standard", "Annotative"]