### Check for existing issues

- [x] I have searched the existing issues and checked that my issue is not a duplicate.

### What happened?

When using Claude Code through LiteLLM's Anthropic `/v1/messages` endpoint with `websearch_interception` enabled, the initial web search interception works, the search provider is called successfully, but the follow-up Anthropic request crashes inside LiteLLM because duplicate keyword arguments are passed to `anthropic_messages.acreate()`.

In my case, the search itself completed successfully, but the agentic follow-up failed with:

1. `got multiple values for keyword argument 'context_management'` 2. after locally hotfixing that, the next failure was `got multiple values for keyword argument 'output_config'`

As a result, Claude Code sees web search as unavailable / unusable even though LiteLLM did perform the search.

## Environment

- LiteLLM: `v1.83.9-nightly` - Release commit: `850fe59` - Claude Code: `2.1.116` - Endpoint used by Claude Code: LiteLLM unified Anthropic endpoint `/v1/messages` - Search provider: SearXNG - Upstream model provider: Anthropic-compatible third-party endpoint - Reproduced on: April 21, 2026

## Relevant config

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