Preserve authored projection content and contextual canvas selection

docs/api.rst

@@ -570,8 +570,15 @@ retain their identities and contracts; migration does not silently replace them.
 ``coverage`` and ``work_contexts``, and ``Name`` for ``exchange_labels``.
 ``{"Only":[]}`` hides all relation and trace lines; ``{"Any":[]}`` preserves
 an explicit empty category/context selection. Category members union within
-each family, and independent filters intersect. ``Traceability`` permits
-references from both layers; ordinary projections require the diagram's layer.
+each family, and independent filters intersect. String projections permit saved
+references and placements from both layers. Only ``Traceability`` renders both;
+other string projections filter to the diagram's declared layer. ``EditDiagram``
+may change between these projections without deleting latent placements, routes
+or visibility choices. Returning to Traceability restores their applicability.
+Typed StateMachine/Scenario views retain their strict membership and layer checks.
+Missing objects, wrong reference kinds/families and duplicate selections remain
+invalid. Frozen versions 1–6 keep their prior layer admission before migration;
+older version-7 implementations may reject these newly accepted ordinary views.
 These presentation choices preserve semantic records, routes, placements and
 the automatic port positions derived from unfiltered eligible exchanges.
 

docs/language.rst

@@ -409,8 +409,12 @@ filters rather than widening them to All.
 
 Traceability views retain their established two-layer projection: default options
 preserve eligible OA and SA lines. Their hidden-edge, category and context
-references may therefore select either layer. All ordinary projections require
-these references in the declared diagram layer. A filter never hides the other
+references may therefore select either layer. Ordinary string projections retain
+these references from either layer as saved presentation choices; they still
+render only their declared layer. Switching projections MUST preserve those
+choices, including explicit empty selections. Existing-object, reference-kind,
+family and uniqueness constraints still apply. Typed StateMachine and Scenario
+views retain layer-scoped reference admission. A filter never hides the other
 layer merely because the Traceability diagram has an OA or SA layer label.
 
 Versions 1–5 reject the new relation, category constructor, diagram field (even
@@ -1073,6 +1077,20 @@ capabilities with their involvement, exploitation, include, extend and
 generalization links. Decomposition and Overview retain general containment;
 Overview also exposes all relationships. These string projections hide
 inapplicable placements without deleting them or changing semantic records.
+This includes opposite-layer placements retained after leaving Traceability.
+Changing between string projections changes only the projection value; placement
+identities, positions, sizes, collapsed state, port anchors, routes and visibility
+choices remain authored. Returning to Traceability restores their applicability.
+Ordinary views MUST NOT render opposite-layer nodes, parents, ports or lines.
+This current-version admission correction does not broaden frozen source/JSON
+versions 1–6: their layer-scoped placement and visibility checks remain required
+before migration. Earlier version-7 implementations can reject ordinary views
+containing these retained opposite-layer records.
+
+The explicit RelocateNode operation moves a placement to a different diagram
+only when its element belongs to the destination layer or the destination is
+Traceability. Retaining an existing hidden placement through a projection change
+does not authorize a relocation that immediately hides it in another layer.
 
 A StateMachine projection MUST reference an existing StateMachine in the
 diagram's layer. Its placements MUST refer to that machine, its Regions, or

docs/openapi.json

@@ -12490,7 +12490,7 @@
         },
         "required": [],
         "additionalProperties": false,
-        "description": "Presentation only. Independent predicates intersect; category members union within a family. Only([]) hides all relations and traces. Any([]) remains an explicit empty selection. Traceability permits both-layer hidden/category/context references; ordinary projections require the diagram layer. Filtering preserves unfiltered automatic port positions."
+        "description": "Presentation only. Independent predicates intersect; category members union within a family. Only([]) hides all relations and traces. Any([]) remains an explicit empty selection. String projections preserve both-layer hidden/category/context references and latent placements; only Traceability renders both layers. Typed StateMachine/Scenario views retain layer-scoped admission. Filtering preserves unfiltered automatic port positions."
       },
       "CommunicationPortChoice": {
         "oneOf": [