Serializes the flow — plus every flow it references through subflow nodes — into a
tenant-neutral, credential-free JSON bundle that can be imported into any tenant with
the import operation. Tenant-scoped references (connections, Datastore tables, global
variables) are declared as named requirements and rebound at import time; policy and
Slack-channel references cannot travel and are recorded as unsupported references.
The bundle never contains credentials, tenant identifiers, schedules, or execution state.