fix(openai): require nested strict schema fields

[Seth Juarez (sethjuarez)]

Summary

• make OpenAI strict JSON Schema conversion recursively include every nested object key in required
• preserve Prompty optionality by rendering non-required fields as nullable unions
• pin the behavior in the canonical shared wire vectors and specification
• load generated property subtypes in the TypeScript vector harness so nested schemas are exercised faithfully
• exercise the exact nested optional case in the ignored live Rust integration test

Runtime audit

Runtime	Result
Rust	Fixed recursive nested required generation
Python	Already compliant; new shared vector passes
TypeScript	Provider already compliant; vector harness now preserves nested generated properties
C#	Already compliant; new shared vector passes
Go / Swift	No OpenAI provider surface on main
Java	Matching fix and live regression coverage are in PR #444 (2355dbe1, da5a3f6e)

Verification

• cargo test -p prompty-openai
• cargo fmt --all -- --check
• uv run pytest tests/test_spec_vectors.py tests/test_executor.py tests/test_structured.py -q (219 passed, 17 skipped)
• npm run test --workspace @prompty/core -- spec-vectors.test.ts (140 passed, 17 skipped)
• npm run test --workspace @prompty/openai (91 passed, 18 skipped)
• npm run lint --workspace @prompty/core
• C# SpecVectorWireTests assembly run (25 passed)
• live OpenAI test_structured_output E2E: accepted the nested strict schema and returned {"style":{"border":null,"color":"blue"}}
• Java PR Add a Java runtime built on generated models #444: the canonical vector passes unmodified; reverting Java's one-line fix creates exactly one failure at response_format.json_schema.schema.properties.style.required (expected 2 keys, got 1), then the restored fix passes all 695 tests

The live Java negative check also reproduced OpenAI's nested-schema rejection verbatim: In context=('properties', 'address'), 'required' is required to be supplied and to be an array including every key in properties. Missing 'postcode'.

The contract matches OpenAI's Structured Outputs guidance: all fields must be required, optional fields are modeled with null, and the rule applies to nested object schemas.

[Copilot]

Pull request overview

This PR tightens Prompty’s OpenAI Structured Outputs “strict” wire contract so that every object property is listed in required recursively, while Prompty-optional fields are modeled as nullable unions (e.g., type: ["string", "null"]). It updates both the normative spec/docs and the shared wire vectors, and adjusts harnesses/tests so nested schemas are exercised end-to-end.

Changes:

• Updated the wire-format specification/docs to define strict-mode recursive required behavior and nullable modeling for optional fields.
• Added a new canonical wire vector (structured_output_nested_optional) that asserts nested optional handling in strict mode.
• Updated TypeScript vector harness loading to use generated Property.load(...) (preserving nested property shapes) and updated Rust wire/tests to require nested properties under strict mode.

Show a summary per file

File	Description
web/src/content/docs/specification/wire-format.mdx	Documents strict-mode recursive required + nullable optionals in schema conversion.
spec/vectors/wire/wire_vectors.json	Adds canonical nested-optional structured output wire vector + expected strict schema.
spec/spec.md	Updates normative spec text/pseudocode for strict schema generation rules.
runtime/typescript/packages/core/tests/spec-vectors.test.ts	Uses Property.load so vectors preserve generated nested property subtypes.
runtime/rust/prompty-openai/tests/wire_vectors.rs	Exercises the new vector and updates strict nested required assertions.
runtime/rust/prompty-openai/tests/integration.rs	Updates ignored live test to validate nested optional strict output is nullable + required.
runtime/rust/prompty-openai/src/wire.rs	Ensures strict mode includes nested properties in required arrays (recursive behavior).

Review details

• Files reviewed: 7/7 changed files
• Comments generated: 0
• Review effort level: Lite