Migrate frozen data contracts and authored source to schema 4

crates/oa-core/src/migration_v2/README.md

@@ -11,10 +11,12 @@ but constructs and validates the frozen DTO, preserves located old-contract
 errors, then calls `adapter.rs`. Original staged scenario/state defaults and
 generic port/optional FE endpoint contracts therefore remain explicit.
 
-`adapter.rs` budgets generated data, validates V2, transforms only the changed
-payloads, and validates schema 3. Serialization between the two typed DTOs copies
-unchanged fields; original input bytes are never deserialized into the new
-`Project`. V1 normalization also constructs this V2 DTO before the shared stage.
+`adapter.rs` budgets generated data, validates V2 and transforms only the changed
+port/endpoint payloads into an explicit schema 3 candidate. The schema 3 reader
+then performs the data-contract upgrade and validates schema 4. Serialization
+between compatibility DTOs copies unchanged fields; original input bytes are
+never deserialized into the new `Project`. V1 normalization also constructs this
+V2 DTO before the shared stages. Combined generation stays within one budget.
 
 Do not update these frozen shapes when extending the current model. Add another
 versioned migration when the persistent contract changes again. Golden V2

crates/oa-core/src/migration_v2/adapter.rs

@@ -62,16 +62,9 @@ pub(crate) fn migrate(
             }],
         });
     }
-    let mut report = MigrationReport {
-        from_schema: 2,
-        to_schema: 3,
-        preserved_ports: vec![],
-        generated_endpoints: vec![],
-        orientation_defaults: vec![],
-        required_resolutions: vec![],
-    };
+    let mut report = MigrationReport::data_upgrade(2);
     let mut value = serde_json::to_value(&old)?;
-    value["schema_version"] = Value::from(SCHEMA_VERSION);
+    value["schema_version"] = Value::from(3);
     for element in old.elements.values() {
         if let Some(super::model::SharedBody::Port {
             direction,
@@ -204,11 +197,23 @@ pub(crate) fn migrate(
             _ => {}
         }
     }
-    let project: Project = serde_json::from_value(value)?;
-    limits.check_model(&project).map_err(FileError::Limit)?;
-    super::super::validate_project(&project)?;
+    // Carry the endpoint-generation reference charge into the next migration;
+    // independent per-stage checks would undercount the combined generated graph.
+    let data_limits = ParseLimits {
+        max_step_references: limits
+            .max_step_references
+            .saturating_sub(additional_references),
+        ..limits
+    };
+    let migrated = super::super::v3::migrate(serde_json::from_value(value)?, data_limits)?;
+    let data = migrated
+        .migration
+        .expect("the schema3 adapter reports its defaults");
+    report.semantic_defaults = data.semantic_defaults;
+    report.generated_interface_allocations = data.generated_interface_allocations;
+    report.unresolved_message_values = data.unresolved_message_values;
     Ok(DecodeResult {
-        project,
+        project: migrated.project,
         migration: Some(report),
     })
 }