TML-2839: prevent factory output from overriding bound scaffold fields in mongo buildBoundContract

Spread only the factory's declared outputs (models/valueObjects/roots) via
ifDefined instead of the whole factory return, so a factory cannot clobber the
pre-bound family/target/extensionPacks. Follow-up to the CodeRabbit finding on
#730 (TML-2817), which merged before it was addressed.

Signed-off-by: Will Madden <madden@prisma.io>

Author: wmadden

packages/2-mongo-family/2-authoring/contract-ts/src/contract-builder.ts

@@ -1721,7 +1721,13 @@ export function buildBoundContract<
       rel,
       valueObject,
     } as unknown as ContractAuthoringHelpers<F, T, NonNullable<Definition['extensionPacks']>>;
-    return buildContractFromDefinition({ ...full, ...factory(helpers) });
+    const built = factory(helpers);
+    return buildContractFromDefinition({
+      ...full,
+      ...ifDefined('models', built.models),
+      ...ifDefined('valueObjects', built.valueObjects),
+      ...ifDefined('roots', built.roots),
+    });
   }
 
   return buildContractFromDefinition(full);