* fix(oauth): inject billing header for non-Haiku model access
The Anthropic Messages API requires a billing identification block
in the system prompt when using Claude Code OAuth tokens (sk-ant-oat*)
to access non-Haiku models (Opus, Sonnet). Without it, the API returns
a generic 400 "Error" with no actionable detail.
This was discovered by intercepting Claude Code CLI requests — the CLI
injects an `x-anthropic-billing-header` text block as the first system
prompt entry on every request. Third-party consumers of the same OAuth
tokens must do the same.
Changes:
- Add `_apply_oauth_billing()` to `ClaudeChatModel` that prepends the
billing header block to the system prompt when `_is_oauth` is True
- Add `metadata.user_id` with device/session identifiers (required by
the API alongside the billing header)
- Called from `_get_request_payload()` before prompt caching runs
Verified with Claude Max OAuth tokens against all three model tiers:
- claude-opus-4-6: 200 OK
- claude-sonnet-4-6: 200 OK
- claude-haiku-4-5-20251001: 200 OK (was already working)
Closes#1245
* fix(oauth): address review feedback on billing header injection
- Make OAUTH_BILLING_HEADER configurable via ANTHROPIC_BILLING_HEADER env var
- Normalize billing block to always be first in system list (strip + reinsert)
- Guard metadata with isinstance check for non-dict values
- Replace os.uname() with socket.gethostname() for Windows compat
- Fix docstrings to say "all OAuth requests" instead of "non-Haiku"
- Move inline imports to module level (fixes ruff I001)
- Add 9 unit tests for _apply_oauth_billing
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
---------
Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>
