MCP tool search is tried behind custom endpoints and held off in conversations that ran without it

What

MCP tool search lets Claude look up extra tools when it needs them instead of loading them all at the start, through the ToolSearch tool. This release changes two situations where Claude Code turns it off by itself.

• Custom API endpoints. ANTHROPIC_BASE_URL points Claude Code at a proxy or gateway instead of Anthropic's own servers. Before, tool search was switched off straight away when that address was not a first-party Anthropic host. Now the request is sent with tool search anyway. If the endpoint refuses it and answers without tool search, Claude Code stores the time of the refusal (toolSearchRefusedAt) for that endpoint and model, logs a warning, and keeps tool search off there for a day.
• Conversations that ran without it. If a conversation has already run without ToolSearch, tool search now stays off for the rest of that conversation, until it is compacted (shortened into a summary) or cleared. A message says so, and the decision is recorded with the reason held_off.

The ENABLE_TOOL_SEARCH setting controls both:

• ENABLE_TOOL_SEARCH=false skips the request that would be refused.
• ENABLE_TOOL_SEARCH=true always sends tool search, turns off the one-day recovery, and overrides the hold-off in a conversation.

The stock ToolSearch description in v2.1.304 is 953 characters, from a capture taken under this release.

Why

If you use a proxy, you are no longer locked out of tool search just because of the address. You get it automatically when the proxy supports it, and after one refusal Claude Code stops trying for a day. Within one conversation the set of available tools now stays the same, which affects how deferred tools such as EndConversation load.