WebSearch gains a standard/extended mode that is off unless configured

What

The WebSearch tool, which Claude uses to search the web, has a new optional search mode that stays off unless a server config or environment variable turns it on. When it is on:

• The tool gets a mode input with two values: "standard", the normal web search that is quick and cheap, and "extended". A "standard" search is sent as a fast search.
• A system hint tells Claude to use "standard" by default and "extended" only when results are thin, out of date or hard to find. It is added to the headless and SDK system prompt and to agent prompts, but only when a WebSearch tool is in the tool list.
• The config can override the mode description and the system hint, and can supply a web_search_addendum that is appended to the WebSearch tool's prompt.

When the feature is off and Claude sends a mode anyway, the field is now removed from the request instead of causing an error.

The feature only turns on when all of these hold: the session uses Anthropic's own API with its own base URL; the config comes from CLAUDE_CODE_WEB_SEARCH_FAST_ARG or, if that is unset, the remote switch tengu_sleepy_shore, and has enabled set to true; and CLAUDE_CODE_WEBSEARCH_USE_CCR_PROXY is not set without CLAUDE_CODE_WEBSEARCH_CCR_PROXY_FAST. tengu_sleepy_shore falls back to no config, and nothing has been read about it yet. A prompt capture taken under this release shows the stock WebSearch description unchanged from the previous release, at 1,322 characters.

Why

None of this changes WebSearch unless the config is set. Once it is, Claude can choose between a cheaper and a more thorough search, and the tool's text can be changed from the server without a new release.