[did2 #12] Corpus end-to-end tests for the migration path

[stevevanhooser]

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

Scope

Run real-world v1 datasets through migration and verify functional equivalence — pre-migration query results == post-migration query results for the same paths.

Pick 2–3 representative test datasets (similar in spirit to DID-matlab/tests/+did2/+unittest/testCorpus*). For each:

Test A: pre-migration baseline. Load v1 dataset, run a representative query mix:

• A few base.* paths (id, session_id, name).
• A few depends_on queries (both via .id legacy and .value V_delta — both must succeed thanks to the compat translator in issue 8).
• At least one collapsed-ontology field (probe_location.ontology_name legacy + probe_location.location.node V_delta).
  Record full result sets.

Test B: migration. Run ndi.migrate.local on the same dataset.

Test C: post-migration verification. Repeat the queries from Test A. Result sets must match Test A's recordings exactly.

Test D: write-path round trip. Open a migrated doc, modify a legacy alias (probe_location.ontology_name = 'new_value'), write back, re-read. The V_delta canonical field (probe_location.location.node) must reflect the new value on disk.

Out of scope

Cloud-side end-to-end — see issue 13.

Dependencies

Issues 3, 5, 6, 7, 8, 9.