fix(honeydew): read and write flat semantic model documents

[baruchoxman]

Summary

Part of #418, for converters/honeydew. #383 moved the Ossie document schema to a single semantic model at the document root, and #397 dropped root-level dialects/vendors. This converter still required the semantic_model: [...] wrapper, so it could not read any current Ossie document — including examples/tpcds_semantic_model.yaml, which its own round-trip test loads. Its CI has not re-triggered since #383, so the break has been latent: test_ossie_roundtrip_tpcds_example is red on main today.

What changed

• Ossie → Honeydew: read the model from the document root; removed the wrapper handling and the multi-model warning (a document now holds exactly one model). A document that still carries the legacy wrapper gets an explicit error telling the author to move the model's properties up to the root, rather than a confusing "missing name".
• Honeydew → Ossie: emit version plus the model's properties at the root, with no wrapper.
• Dropped the vendors round-trip: root-level vendors no longer exists in the schema, and the root is now additionalProperties: false, so emitting it made the output invalid. This also removes the extra_vendors plumbing through the ossie metadata section and the test_vendors_roundtrip case that covered it.
• README: the mapping tables now name name at the document root instead of semantic_model.name.
• Tests: helpers build and assert the flat shape; added a case asserting the legacy wrapper is rejected with the migration message.

Verification

The TPC-DS round-trip now works end to end, and its output validates against the official schema — the converter's first output that the validator has ever accepted since #383:

$ uv run ossie-honeydew ossie-to-honeydew -i examples/tpcds_semantic_model.yaml -o /tmp/hd_ws
Wrote 20 file(s) to /tmp/hd_ws
$ uv run ossie-honeydew honeydew-to-ossie -i /tmp/hd_ws -o /tmp/roundtrip.yaml
$ python3 validation/validate.py /tmp/roundtrip.yaml
Validation PASSED: roundtrip.yaml

Test plan

• cd converters/honeydew && uv sync && uv run pytest — 126 passed (128 on main, of which 1 failed; net −3 test_vendors_roundtrip params, +1 legacy-wrapper case)
• test_ossie_roundtrip_tpcds_example passes, having been red on main
• python3 validation/validate.py accepts the round-tripped TPC-DS document

🤖 Generated with Claude Code

[baruchoxman]

@jbonofre would appreciate you taking a look

[jbonofre]

@baruchoxman absolutely. Thanks!