diff --git a/backends/contracts/premium.py b/backends/contracts/premium.py
index a33679b..f1f090b 100644
--- a/backends/contracts/premium.py
+++ b/backends/contracts/premium.py
@@ -36,11 +36,18 @@ class PremiumContract(ABC):
 
     _plan_spec: PlanSpec | None = None
     _preflight_result: Any = None
+    # The standard `drawing_apply_iso_layers` last bootstrapped on *this*
+    # drawing (None until it runs) — `_active_layer_set_id` reads it ahead of
+    # the PlanSpec. Drawing-scoped like the plan: a live backend clears it
+    # when AutoCAD's active document changes, the headless registry keeps one
+    # per open document.
+    _active_layer_set: LayerSetId | None = None
 
     def _reset_document_state(self) -> None:
         """Clear metadata that is valid only for the current drawing."""
         self._plan_spec = None
         self._preflight_result = None
+        self._active_layer_set = None
         self._gdt_datums_defined = set()
         self._gdt_datums_referenced = set()
 
diff --git a/backends/ezdxf_backend.py b/backends/ezdxf_backend.py
index 92fa017..b119a58 100644
--- a/backends/ezdxf_backend.py
+++ b/backends/ezdxf_backend.py
@@ -977,6 +977,11 @@ class _DocState:
     transaction_stack: list[Path] = field(default_factory=list)
     plan_spec: Any = None
     preflight_result: Any = None
+    # `drawing_apply_iso_layers` records the standard here so `_role_layer`
+    # files dims / scaffolding on that standard's layer; it is per drawing,
+    # not per backend (an iso13567 sheet next to a mech one must not push
+    # the mech drawing's dimensions onto M-DIMEN-T-N).
+    active_layer_set: str | None = None
     gdt_datums_defined: set = field(default_factory=set)
     gdt_datums_referenced: set = field(default_factory=set)
     activated_seq: int = 0
@@ -1033,6 +1038,7 @@ class EzdxfBackend(AutoCADBackend):
     _transaction_stack = _ActiveField("transaction_stack")
     _plan_spec = _ActiveField("plan_spec")
     _preflight_result = _ActiveField("preflight_result")
+    _active_layer_set = _ActiveField("active_layer_set")
     _gdt_datums_defined = _ActiveField("gdt_datums_defined")
     _gdt_datums_referenced = _ActiveField("gdt_datums_referenced")
 
diff --git a/tests/test_documents.py b/tests/test_documents.py
index 7b3b600..4a159d3 100644
--- a/tests/test_documents.py
+++ b/tests/test_documents.py
@@ -88,6 +88,39 @@ async def test_per_document_state_follows_the_active_entry(backend):
     assert backend._dirty is False
 
 
+async def test_active_layer_set_is_per_document(backend):
+    """The standard ``drawing_apply_iso_layers`` bootstrapped is per drawing.
+
+    It drives ``_role_layer`` — where ``dimension_auto`` and
+    ``construction_xline`` file their output — and the critique that checks
+    them. Held on the backend it bled across documents: an iso13567 sheet
+    next to a mech one pushed the mech drawing's dimensions onto
+    ``M-DIMEN-T-N`` (created on demand), silently, and ``drawing_critique``
+    could not see it because the same stale set drove the critique.
+    """
+    await backend.drawing_apply_iso_layers("iso13567")
+    assert backend._role_layer("dim") == "M-DIMEN-T-N"
+
+    second = (await backend.drawing_new())["document"]
+    assert backend._active_layer_set is None, "a fresh drawing has no explicit set"
+    assert backend._role_layer("dim") == "DIM"
+    line = await backend.entity_create_line(0, 0, 50, 0)
+    dims = await backend.dimension_auto([line.handle], style="chain")
+    assert dims[0].layer == "DIM"
+    assert "M-DIMEN-T-N" not in [lyr.name for lyr in await backend.layer_list()]
+
+    # Bidirectional: switching back restores the first document's set …
+    await backend.document_activate("untitled-1")
+    assert backend._active_layer_set == "iso13567"
+    assert backend._role_layer("construction") == "M-CONST-E-N"
+    # … and a set applied on B while A is open does not reach A.
+    await backend.document_activate(second)
+    await backend.drawing_apply_iso_layers("pid")
+    assert backend._role_layer("dim") == "DIM"
+    await backend.document_activate("untitled-1")
+    assert backend._active_layer_set == "iso13567"
+
+
 async def test_opening_a_file_twice_reloads_it_instead_of_registering_twice(backend, tmp_path):
     path = tmp_path / "part.dxf"
     await backend.drawing_save(str(path))
@@ -495,6 +528,7 @@ async def test_com_activate_calls_activate_and_resets_document_scope(com_backend
     backend, app = com_backend
     await backend._ensure_document_state()
     backend._plan_spec = object()
+    backend._active_layer_set = "iso13567"
     result = await backend.document_activate("Second.dwg")
     assert result == {
         "ok": True,
@@ -505,6 +539,8 @@ async def test_com_activate_calls_activate_and_resets_document_scope(com_backend
     }
     assert app.Documents._docs[1].calls == [("Activate", ())]
     assert backend._plan_spec is None, "a document switch clears drawing-scoped state"
+    assert backend._active_layer_set is None, "the layer set is drawing-scoped too"
+    assert backend._role_layer("dim") == "DIM"
     with pytest.raises(ValueError, match="no open document named 'Third.dwg'"):
         await backend.document_activate("Third.dwg")