Summary

• Preserve JSON Schema union type lists when sanitizing Moonshot tool schemas
• Avoid unhashable-list crashes in _fill_missing_type() and scalar enum cleanup
• Add a regression test for sanitize_moonshot_tools() with type: ["number", "string"]

Fixes #28291

Test Plan

• RED: python -m pytest tests/agent/test_moonshot_schema.py::TestToolListSanitizer::test_preserves_json_schema_union_type_lists -q failed with TypeError: unhashable type: 'list'
• GREEN: python -m pytest tests/agent/test_moonshot_schema.py -q → 43 passed, 11 warnings
• python -m ruff check agent/moonshot_schema.py tests/agent/test_moonshot_schema.py → All checks passed
• git diff --check