Define ScheduleUpdate null and omission semantics during schedule implementation

[coderabbitai]

Summary

Define the update semantics for ScheduleUpdate when the schedule persistence and update flow are implemented.

ScheduleUpdate currently permits null for fields that are non-nullable on Schedule:

• modules
• module_configuration
• recurrence_rule
• timezone
• enabled

The published OpenAPI contract currently makes these fields nullable. A client can therefore send explicit JSON null. The API contract must distinguish an omitted field from an explicitly supplied null value.

Required changes

• Decide the API behavior for explicit JSON null values in PATCH /api/v1/schedules/{schedule_id}.
• Keep omitted fields unchanged during a partial update.
• Reject explicit null values for fields that cannot be null on Schedule, unless the final persistence model intentionally supports null for that field.
• Implement the selected behavior in the request schema and schedule update merge/application flow.
• Update the generated OpenAPI contract if the selected behavior changes the schema.
• Add tests for omitted fields, valid field updates, and explicit null values.

Affected areas

• src/nc3_testing_platform/domains/schedules/schemas.py
• src/nc3_testing_platform/domains/schedules/router.py
• Future schedule service and repository modules
• api/openapi.json
• Schedule update tests

Acceptance criteria

• An omitted update field does not modify the stored Schedule value.
• A valid supplied update field modifies the stored Schedule value.
• An explicit null value cannot produce a Schedule with null values for modules, module_configuration, recurrence_rule, timezone, or enabled.
• The generated OpenAPI schema matches the implemented request behavior.
• Tests cover the selected semantics.

Backlinks

• PR: feat(api): v4.0.1 OpenAPI contract, contract-first source, and specs #1
• Review comment: feat(api): v4.0.1 OpenAPI contract, contract-first source, and specs #1 (comment)

Requested by: @t0kubetsu