The worker hardcoded response_format={type:json_object}, which LM Studio
rejects with 400 ('must be json_schema or text'); it also leaves
reasoning models (Gemma) with an empty `content`. Fix:
- Default to response_format=json_schema with the real analysis schema
(prompt::output_json_schema), which LM Studio accepts and which forces
clean JSON into message.content. Configurable via ANALYSIS_RESPONSE_FORMAT
= json_schema (default) | json_object | none (config::ResponseFormat).
- build_request_body is now a pure, unit-tested function.
- Vision errors now include the server's response body (status + text)
instead of a bare status, so a 400's reason is visible in logs.
Tests: response-format body shapes (none/json_object/json_schema), schema
shape + round-trip with the DTO, config parsing/defaults.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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