WebSearch tool returns 400 invalid request parameters on all queries

Summary

WebSearch tool consistently returns API Error: 400 invalid request parameters: invalid request for valid queries. Reproduced just now across three different multi-word queries in a single session.

Repro

In Claude Code session (Opus 4.7), invoke WebSearch with any reasonable query, e.g.:

• agentic second brain LLM memory system best practices 2026 hierarchical retrieval
• Claude Code hooks memory file based agent context engineering patterns
• PARA method Zettelkasten LLM agent retrieval team knowledge base

All three returned identically:

API Error: 400 invalid request parameters: invalid request

No domain filters, no allowed_domains / blocked_domains, just the query field.

Expected

Search results, or at minimum a more actionable error (rate-limit, auth, query-too-long, region-restricted, etc).

Environment

• macOS (Darwin 25.5.0)
• Claude Code, model claude-opus-4-7
• Date: 2026-05-26
• Reproduced in 3/3 attempts in same session

Notes

The tool prompt mentions web search is US-only — if that's the cause, the error message should say so rather than returning a generic 400. From the user's perspective WebSearch just looks broken.