[Feature Request] Keep an explicit header converter on all outgoing paths #851

Related problems

A Header can carry its own data converter: Header::fromValues($values, $converter).
Most outgoing paths ignore it and always set the client or worker converter:

• workflow start: src/Internal/Client/WorkflowStarter.php:385
• ActivityClient: src/Client/ActivityClient.php:266
• schedules: src/Internal/Mapper/ScheduleMapper.php:42
• worker commands: src/Worker/Transport/Codec/ProtoCodec/Encoder.php:53, src/Worker/Transport/Codec/JsonCodec/Encoder.php:48

After #839, update and update-with-start keep the explicit converter. So the behavior now differs by path.

In Go, Java, Python and TypeScript, the code that writes a header picks the encoding. The SDK does not apply the client converter to header values.

Solution

Use one rule on all paths: the header converter if set, else the client or worker converter.
Prebuilt Payload entries stay unchanged, as now.

This changes current behavior for headers with an explicit converter. Align it with the cross-SDK decision in temporalio/features#850 (possibly opt-in).

Additional context

• Normalize Header Data Conversion across languages features#850
• Fix data converter assignment for update headers #839