[parbhatkapila4]

What was changed

With external storage configured, the payload converter and failure converter lose their serialization context. _with_contexts calls with_context() and then _with_store_context(). The second step uses dataclasses.replace, which reruns __post_init__ and builds new payload and failure converters from their classes, so the context-bound instances are dropped. Only the codec keeps its context, because it's an init field.

So any converter that implements WithSerializationContext gets None instead of the workflow or activity context on client calls and in the workflow and activity workers, as soon as external storage is set. This happens for every payload, not just those that go to storage.

The fix keeps the current converters on the clone, as with_context() does.

How was this tested

Parametrized test_payload_conversion_calls_follow_expected_sequence_and_contexts to also run with external storage (in-memory driver). On main, the new case fails with "Unexpected context type: NoneType" in the payload converter. With the fix, both cases pass. The rest of test_serialization_context.py and the extstore and converter tests pass the same as on main.