raise the Anthropic request body limit to 64 MiB

[rikbrown]

Problem

MAX_OPENAI_REQUEST_BYTES is 16 MiB. An image-heavy Claude Code session (~490k tokens of screenshots) pushes the request body past that, and because Claude Code re-sends the full history on every turn, the gate then rejects every subsequent request on that session — the session is unrecoverable without dropping the transcript.

Fix

Raise the limit to 64 MiB, matching the Codex image edit cap already used in providers::codex::images, so the two paths agree on how large an image-bearing request may be.

MAX_PROVIDER_STREAM_BYTES (32 MiB) and MAX_SSE_EVENT_BYTES (2 MiB) are untouched — those bound responses, which this does not change.

Verification

Tests in tests/server.rs cover the boundary directly:

• a body at the limit clears the gate
• a body over the limit still returns the length error
• a body over the old 16 MiB limit now clears the gate

cargo clippy --all-targets -- -D warnings clean, cargo fmt --check clean, full suite green.

🤖 Generated with Claude Code

[RichAyotte]

Raising MAX_OPENAI_REQUEST_BYTES also raises /v1/chat/completions and /v1/responses, which still read that constant.

messages_body_over_limit_returns_length_error still expects 400 with length limit exceeded. Anthropic's Messages and Token Counting APIs document 413 request_too_large for overflow (https://platform.claude.com/docs/en/api/errors#request-size-limits).

[raine]

Thanks for this! The larger limit fixes the image-heavy session case nicely. I split the Anthropic limit from the OpenAI-compatible endpoints and corrected oversized Anthropic requests to return 413 request_too_large. Merged.