Small vision models (qwen3-vl-4b) sometimes loop the OCR array, running
the response into the token ceiling (finish_reason: length) and failing to
parse. Layered guardrails:
- Prompts: explicit "transcribe each element once, never repeat/loop, at
most N, STOP when done" in the OCR, grounding and combined prompts.
- Schema: hard maxItems on ocr_results/tagging_results/content_type and
maxLength on text/scene — LM Studio's grammar enforces these, so a loop
is grammar-bounded rather than relying on max_tokens.
- Sampling: a configurable frequency_penalty (ANALYSIS_FREQUENCY_PENALTY,
default 0.3) sent with each request — the decode-time lever that actually
breaks loops.
- Code: sanitize() collapses runaway consecutive duplicates (same
normalized text + kind) so a loop that slips through still can't flood
the row.
Tests: schema caps present, frequency_penalty included only when nonzero,
sanitize collapses consecutive repeats; config default.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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