#60: streamText had no maxOutputTokens, so one anonymous request could run up
the provider bill. Add maxOutputTokens (env SHARE_AI_MAX_OUTPUT_TOKENS, default
512) via resolveShareAiMaxOutputTokens().
#95: the anonymous path hand-built error strings, diverging from the unified
describeProviderError format used on the authenticated path; both onError blocks
now call describeProviderError so a share reader sees 402/429/503 causes in the
same form (and the stack is still logged). Both changes are in this one file and
share hunks, hence one commit.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>