fix shared variant ordering bug

[joe-clickhouse]

Summary

ClickHouse's DataTypeVariant constructor sorts its members alphabetically by name, and the wire-format discriminator byte indexes into that sorted order. The client was appending SharedVariant to the end of the variant list without sorting, so any Dynamic/JSON path whose type name sorted after "SharedVariant" (e.g. UInt*, Tuple(...), UUID) was decoded through the wrong variant reader.

The fix is one line in read_dynamic_prefix where we sort variant_types by name after appending SharedVariant.

Closes #712.

Checklist

Delete items not relevant to your PR:

• Unit and integration tests covering the common scenarios were added
• A human-readable description of the changes was provided to include in CHANGELOG

[joe-clickhouse]

@codex[agent] can you review this PR according to the guide in .agents/review.md

[Codex]

@codex[agent] can you review this PR according to the guide in .agents/review.md

Findings: no issues spotted. Sorting SharedVariant into the variant list before reading discriminators matches the server’s sorted ordering, and the new JSON/Dynamic cases exercise both clients via param_client. Open: I did not rerun the suite locally; relying on the added coverage and existing CI.

[joe-clickhouse]

@claude[agent] can you review this PR according to the guide in .agents/review.md

[Claude]

@claude[agent] can you review this PR according to the guide in .agents/review.md

Review of PR #[Fix shared variant ordering bug]

I've reviewed this PR according to .agents/review.md. The fix is correct and well-tested.

Findings

No material issues found. The PR correctly addresses the root cause.

Code Analysis

Core fix (dynamic.py:224): The one-line sort is correct. I verified against the ClickHouse server source:

• Server code in src/DataTypes/DataTypeVariant.cpp:26-47 uses std::map<String, DataTypePtr> to sort variants alphabetically by name before pushing them to the variants list
• Server code in src/DataTypes/Serializations/SerializationDynamic.cpp:398-399 appends SharedVariant and passes to DataTypeVariant constructor, which sorts
• Client now replicates this exact behavior

Sync/async parity: ✓ No issue. The fix is in read_dynamic_prefix, which is shared serialization logic called by both sync and async read paths through _read_column_binary.

Tests: ✓ Well-covered

• test_json_path_sorts_after_shared_variant and test_dynamic_uint64_single_variant use param_client and call fixtures from conftest.py:221-240,134-139, which run tests in both sync and async modes
• test_dynamic_prefix_sorts_shared_variant is a focused unit test that validates the sorting directly on wire-format bytes

CHANGELOG: ✓ Entry is clear, accurate, and follows repo style. Explains the problem and the fix at the right level of detail.

Public API: ✓ No changes to public surface. This is pure read-path correctness.

Compatibility: ✓ No compatibility concerns. This is a bug fix that restores correct behavior for types sorting after "SharedVariant" alphabetically (UInt*, Tuple, UUID, etc.). There is no backward compatibility to preserve here, the old behavior was wrong.

Minor Observations

• The fix is extremely surgical and focused
• Test coverage is appropriate for the bug class
• No performance impact
• No optional dependency or packaging changes

The PR is ready to merge.