Bound intermediate text while rendering compact schema composites #558

Motivation

An audit at 6ed3894 found that compact schema output is byte-bounded, but composite rendering accumulates child strings before checking the combined result. Individually valid property descriptions can therefore produce megabytes of temporary text that will be discarded against the 8 KiB describe limit. A synthetic 1,000-property schema with 4,000-character descriptions exhibited roughly 5.5 MB of transient heap growth in a local Node probe. This is illustrative allocation evidence, not a stable performance benchmark.

Behavioral requirements

• Composite schema rendering stops consuming later members once its output byte budget cannot be satisfied.
• Within-budget schemas retain their existing rendered output, ordering, constraints, and reference behavior.
• Oversized schemas retain the existing explicit truncation behavior.
• Count UTF-8 bytes, including composite punctuation and property comments.
• Preserve shared work limits and Node/Workers portability.

Acceptance criteria

• Regression coverage proves rendering stops before visiting later members of an oversized composite, rather than merely bounding the final response.
• Cover wide objects and composite forms, including multibyte text and valid near-boundary output.
• Compare the motivating synthetic case before and after, with measurement limitations stated.
• npm run check passes.

Related prior discovery bounds: #82. Reference investigation: UsefulSoftwareCo/executor#1977. This issue concerns intermediate rendering cost, not OpenAPI ingestion or a new compiler.