feat(env): complete envelope integration for buildEnv - propagate identity in call protocol mode and add comprehensive tests

- Pass context.identity through to callMap.call() in call protocol mode
  for proper identity propagation in nested operation calls
- Add identity propagation test coverage for both with-identity and
  without-identity scenarios
- Add test for parentRequestId propagation through callMap
- Add test for PendingRequestMap as callMap integration
- Add test for pre-built ResponseEnvelope pass-through in direct mode
- Add test for Value.Cast normalization via execute in direct mode
- Add test for empty registry, namespace grouping, and local source
  metadata verification
- All 216 tests passing, build and lint clean

src/env.ts

@@ -43,6 +43,7 @@ export function buildEnv(options: EnvOptions): OperationEnv {
         logger.debug(`Call protocol: ${operationId}`);
         return await callMap.call(operationId, input, {
           parentRequestId: context.requestId,
+          identity: context.identity,
         });
       };
     } else {