Thread existing JSON schemas from prompt definitions through the
text-completion service to LLM backends' native structured output
APIs. When a prompt has response-type "json" and a strict-mode
compatible schema, the LLM constrains token selection at the logit
level to guarantee schema-valid output.
Wire-level changes:
- Add response_format and schema fields to TextCompletionRequest
- Update translator to encode/decode new fields
- Pass new fields through LlmService, TextCompletionClient, and
PromptManager
Runtime schema compatibility checker:
- New is_strict_mode_compatible() utility validates schemas against
LLM provider constraints (additionalProperties, required fields,
no unsupported constraints, no open-ended objects)
- Per-prompt eligibility decision: compliant schemas use structured
output, non-compliant schemas fall back to free-text + post-hoc
validation
LLM backend implementations:
- OpenAI: response_format with json_schema, variant-aware top-level
array rejection (openai variant blocks, llama/vllm variants allow)
- New vllm variant for the OpenAI backend
- vLLM (dedicated): response_format in raw HTTP body
- Ollama: format=<schema> parameter
- Claude: tool-use trick (forced tool call with schema as input_schema)
- Mistral: native json_schema response_format
- Llamafile, LM Studio: OpenAI SDK response_format
- Azure OpenAI: AzureOpenAI SDK response_format
- Azure serverless: response_format in raw HTTP body
- TGI: response_format in raw HTTP body
- VertexAI Gemini: response_mime_type + response_schema
- VertexAI Claude: tool-use trick
- Google AI Studio: response_mime_type + response_schema
- Bedrock, Cohere: signature-only (no structured output yet)
Post-hoc jsonschema.validate() retained as defence-in-depth.
Tech spec added: docs/tech-specs/structured-output.md
Update tests
