[Bug] Headers are not propagated to scheduled workflows

[LarsAlmgren]

What are you really trying to do?

Headers was recently added (temporalio/features#703) but haven't been released yet.
I built the version from main branch and tested it, but it seems like headers are not propagated when I use them in schedules.
I expect headers to be included in the workflows triggered by schedules, in the same way as they are when I start workflows with the cli using --headers flag.

Describe the bug

Headers are not included in scheduled workflows.

Minimal Reproduction

Build from master branch and then schedule any workflow using the headers flag. When the workflow executes the headers will not be included.

go run ./cmd/temporal schedule update \
    --schedule-id "example_18_schedule" \
    --interval 5m \
    --task-queue master/etl \
    --type example \
    --input 'Hello world' \
    --input false \
    ----headers 'MyHeader={"ID":18}'

Environment/Versions

• OS and processor: M4 Pro Mac
• Temporal Version: Temporal Cloud
• Building the cli from source

Additional context

[chaptersix]

The --headers flag works for workflow start and workflow execute by injecting headers into the gRPC context at invocation time. However, for schedules, headers need to be stored on the schedule action itself since the workflow is started later by the server.

This requires changes in both the server (to accept and store headers on the schedule action) and the Go SDK (to add a Header field to ScheduleWorkflowAction). Once those are in place, the CLI can wire the --headers flag through to schedule create/update.

The linked feature (temporalio/features#703) was about adding --headers to the CLI for direct workflow starts, which is implemented. Propagating headers to scheduled workflows is a separate capability that requires server and SDK changes first.