[Fix] Prefer operational_dataset_hex over live OTBR dataset in ThreadAutoConfig

[rquidute]

Fixes NFC-Thread commissioning failures (TC-DD-3.23, TC-DD-3.24) where the Thread dataset passed to the SDK diverged from the dataset encoded in the NFC tag, causing ContinueCommissioningAfterConnectNetworkRequest to time out on FindOperationalForStayActive.

Changes

• backend/app/schemas/test_environment_config.py

  • Added operational_dataset_hex: Optional[str] = None to ThreadAutoConfig

• backend/test_collections/matter/sdk_tests/support/python_testing/models/utils.py

  • In __thread_dataset_hex(), when ThreadAutoConfig has operational_dataset_hex set, use it directly instead of querying the live OTBR via ot-ctl dataset active -x

Motivation

When a project config contains ThreadAutoConfig fields (rcp_serial_path, dataset, etc.) alongside operational_dataset_hex, Pydantic was silently dropping operational_dataset_hex because the field was not declared on the model. As a result, __thread_dataset_hex() always fell through to border_router.active_dataset, which queries the live OTBR and may return a different dataset than what the NFC tag was programmed with. The DUT would join a Thread network the TH controller didn't know about, and operational mDNS discovery would time out after 45 seconds.

This was confirmed by testing: creating a new CLI project via scripts populated the config with the full ThreadAutoConfig shape plus operational_dataset_hex. The hex was dropped by Pydantic, the live OTBR returned a mismatched dataset, and commissioning failed. Using a config with only operational_dataset_hex (matching the GUI project shape) passed in all scenarios.

Impact

• No breaking changes. The fix is purely additive — operational_dataset_hex is optional with a None default, so existing ThreadAutoConfig configs without the field are unaffected.
• When operational_dataset_hex is not set, behaviour is identical to before: the live OTBR dataset is fetched via active_dataset.
• Fixes TC-DD-3.23 and TC-DD-3.24 for CLI projects configured with ThreadAutoConfig + operational_dataset_hex.

Releated Issue

[#1004](project-chip/certification-tool#1004

Testing

Unit tests passing

Requesting originator to test in PRs branch - Waiting for feedbacks

[gemini-code-assist]

Code Review

This pull request introduces the operational_dataset_hex field to the ThreadAutoConfig schema and updates the Thread dataset retrieval logic to support this new optional configuration. However, a critical issue was identified: wrapping the OTBR startup and topology formation inside the else block prevents the OTBR container from starting when operational_dataset_hex is provided. The reviewer suggested a code modification to ensure the OTBR container is always started and configured, using the hex dataset as an override only for the returned value.

[oxesoft]

Cherry-picked to v2.16-develop