fix(domain-and-input-skeleton): locate extra instance diagnostic

src/fesa/io/abaqus/semantic_mapper.cpp

@@ -181,10 +181,14 @@ private:
 
         active_assembly_ = &*deck_.assembly;
         if (active_assembly_->instances.size() != 1U) {
+            const SourceLocation& source =
+                active_assembly_->instances.size() > 1U
+                    ? active_assembly_->instances[1].source
+                    : active_assembly_->source;
             add_error(
                 "abaqus.semantic.instance_count",
                 "Phase 1 requires exactly one Instance.",
-                active_assembly_->source);
+                source);
             return false;
         }
 

tests/integration/io/minimal_deck_to_domain_test.cpp

@@ -256,7 +256,13 @@ TEST(ActiveInstance, RejectsMultipleInstances) {
     const auto result = parse_and_map(input.path());
 
     EXPECT_FALSE(result.domain.has_value());
-    EXPECT_TRUE(has_diagnostic(result, "abaqus.semantic.instance_count"));
+    const auto diagnostic = std::ranges::find(
+        result.diagnostics,
+        std::string_view{"abaqus.semantic.instance_count"},
+        &fesa::Diagnostic::code);
+    ASSERT_NE(diagnostic, result.diagnostics.end());
+    ASSERT_TRUE(diagnostic->source.has_value());
+    EXPECT_EQ(diagnostic->source->line, 6U);
 }
 
 }  // namespace