Admit Scenario layout through the ordinary source parser inventory

crates/oa-core/src/source_defaults.rs

@@ -52,7 +52,13 @@ pub(crate) fn parser_fields(context: Context) -> Map<String, Value> {
                 _ => &["source", "target"],
             }
         }
-        Context::Diagram => &[],
+        Context::Diagram => {
+            // Admit the optional payload without restoring a synthetic null in
+            // CompleteForEdit: absence there distinguishes a real layout clear
+            // from an unrelated edit beside an authored explicit `layout none`.
+            fields.insert("layout".into(), Value::Null);
+            &[]
+        }
         Context::Node => &["element"],
         Context::Artifact => &["owner"],
         Context::Trace => &["oa", "sa"],

harness/scenario-text-union-20260923.md

@@ -52,8 +52,15 @@ child 1, preserving the Properties/Connections reconciliation fix.
 
 ## Verification to perform after compiler lease
 
-Rustfmt parsing and Git whitespace/conflict-marker checks precede the source
-commit. No compiler, tests or GUI have run for this candidate at this checkpoint.
+Rustfmt parsing and Git whitespace/conflict-marker checks preceded the initial
+source commit. The first frozen `0b61771` core listing compiled and listed 129
+tests. Its `scenario_layout` run passed 20 and failed seven source lifecycle
+cases: the ordinary parser's field inventory did not admit `layout`. The repair
+adds the optional field to Diagram's parser inventory only, preserving the
+CompleteForEdit omission/clear distinction above. These first receipts bind 742
+unchanged inputs and the actual executable; they are failed-run evidence, not
+acceptance of the repaired source. A fresh listing and affected runs are required.
+No desktop runtime or GUI gate has run at this checkpoint.
 New discriminating tests combine ordinary omitted/authored defaults with
 Scenario row reorder, alias rename and layout clear, and retain a live saved
 spacing gesture across stale Text commands and prior Scenario visit messages.