[did2 #13] Cross-version cloud test: old NDI + new NDI on the same dataset

[stevevanhooser]

Part of the NDI-matlab did2 migration. Target branch: Vnext.

Scope

The migration window must not break customers running older NDI versions against a shared cloud dataset. Verify that an old client (v1-only) and a new client (V_delta-with-compat) can both read the same cloud dataset before, during, and after migration.

Test harness with two MATLAB processes/configurations:

• Old client: NDI at main-version (v1-only).
• New client: NDI at Vnext (V_delta with +ndi/+compat/ layer).

Scenarios:

Scenario 1 — pre-migration coexistence. Both clients read a v1 dataset on the cloud. Both succeed for paths they understand.

Scenario 2 — during migration. New client holds the migrationState lease (issue 11) and is pushing converted docs. Old client attempts reads (must succeed) and writes (must receive 423 Locked).

Scenario 3 — post-migration. Dataset is fully V_delta. New client succeeds on all paths. Old client succeeds on reads thanks to the cloud's existing dual-format tolerance (document_properties.base.* fallback chains in DocumentService) — but may not see V_delta-only fields (e.g., the composite probe_location.location.*). Explicitly: "reads succeed" is the promise; "all fields visible to old client" is not.

Out of scope

Making the old client handle V_delta natively. The compat surface is intentionally one-way.

Dependencies

Issues 10, 11.