feat(adapter): support nested XML data

[isaacbmiller]

Closes #8481.
Closes #10102.
Supersedes #8482 with an implementation based on current main.

Summary

• format nested Pydantic outputs, TypedDicts, and lists as nested XML
• show the nested XML schema consistently in system instructions and the final user reminder, including TypedDict child fields
• parse nested and repeated XML elements into signature field types\n- bound recursive Pydantic schema expansion so self-referential models format safely
• retain support for legacy JSON values inside outer XML field tags
• XML-escape string output values so embedded closing tags round-trip safely
• reject malformed XML with AdapterParseError instead of silently truncating values
• preserve existing DSPy transport and multimodal input formatting

What the final prompt looks like

Given a Person output containing a nested Address and list[str] interests, the LM receives this schema in both the system instructions and final user request:

<person><name>...</name><age>...</age><address><city>...</city><country>...</country></address><interests>...</interests> <interests>...</interests></person>

The final user message looks like:

<text>
Ada, 36, lives in London, UK and likes math and machines.
</text>

Respond with the corresponding output fields wrapped in XML tags `<person>`. Use this nested XML structure: <person><name>...</name><age>...</age><address><city>...</city><country>...</country></address><interests>...</interests> <interests>...</interests></person>

A matching response is parsed directly into the declared Pydantic types:

<person>
  <name>Ada</name>
  <age>36</age>
  <address><city>London</city><country>UK</country></address>
  <interests>math</interests>
  <interests>machines</interests>
</person>

The XMLAdapter documentation includes the runnable example, complete system and user prompt, matching response, and parsed result types.

Testing

• pytest -q tests/adapters/test_xml_adapter.py (24 passed)
• pytest -q tests/adapters (278 passed)
• ruff check dspy/adapters/xml_adapter.py
• ruff format --check dspy/adapters/xml_adapter.py
• git diff --check

[greptile-apps]

Greptile Summary

This change adds XML rendering and parsing for nested Pydantic models, TypedDicts, dictionaries, and repeated lists. It also bounds recursive model schema rendering, preserves JSON-in-XML compatibility, and documents the nested XML response format.

Confidence Score: 5/5

No blocking failure remains.

No accepted blocking findings remain after exercising nested TypedDict, recursive Pydantic, XML escaping, and parse round-trip behavior.

T-Rex Logs

What T-Rex did

• Ran the standalone XML adapter nested-path runtime validation script.
• The script exercised module-scope TypedDict fields, self-recursive and mutually recursive Pydantic models, and XML-sensitive nested string values.
• The exact standalone validation source and its captured execution output were verified, and all three scenario assertions passed with no security-impacting XML escaping failure observed.

_{Ran code and verified through T-Rex}

_{Reviews (5): Last reviewed commit: "refactor(adapter): unify XML schema hand..." | Re-trigger Greptile}

[isaacbmiller]

superseded by #10239.