Claude Code → Azure OpenAI: 400 Invalid 'user': string too long (metadata.user_id forwarded verbatim) #5705

Client or integration

Claude Code

Area

Proxy and routing

Summary

Claude Code requests routed to an Azure OpenAI model fail with HTTP 400, because anthropicToResponsesTranslation copies metadata.user_id verbatim into the Responses user field.

Claude Code sends metadata.user_id as a JSON string (device id, account uuid, session id) of about 186 characters. OpenAI-compatible Responses backends such as Azure OpenAI cap user at 64 characters and reject the request. The ChatGPT backend accepts it, so Codex-native routes work, while every Azure route from Claude Code or the Claude Desktop Code tab fails.

The value is copied at src/claude/inbound.ts:445 (body.user = raw.metadata.user_id;). The same block already hashes user_id to build prompt_cache_key.

Reproduction

1. Configure an azure-openai provider (adapter: "azure-openai", base URL https://<resource>.services.ai.azure.com/openai/v1) with gpt-6-astra.
2. Apply the first-party Claude Desktop profile with ocx claude desktop apply, or launch through ocx claude.
3. Run claude -p "Reply only: OK" --model <slot alias of azure-openai/gpt-6-astra>.
4. The request fails. The same prompt sent with curl to /v1/messages without metadata succeeds, and a Codex-native slot such as gpt-5.6-sol (native) succeeds from Claude Code.

Version

2.64.0 (npm, latest)

Operating system

macOS (Darwin 27.0.0, arm64)

Provider and model

azure-openai / gpt-6-astra, gpt-5.6-sol

Logs or error output

API Error: 400 Invalid 'user': string too long. Expected a string with maximum length 64, but got a string with length 186 instead.

Suggested fix

Keep user when it has 64 characters or fewer. Otherwise send the SHA-256 hex digest (64 characters) that the block already computes for prompt_cache_key. I verified this locally: Azure slots answer normally from Claude Code, and native and Anthropic routes are unaffected. A PR follows.