New agent and mcp_tool hook types, enabled through a remote list

What

Hooks are commands or prompts you configure to run automatically at certain moments, such as before a tool runs. Two new hook types are being added:

• An agent hook type, with the fields prompt, if, timeout, model, status_message and once.
• An mcp_tool hook type, which calls a tool on an MCP server (an add-on that supplies tools), with server, tool, input, if, timeout, status_message and once.
• Hooks of these types are only accepted when a list fetched from Anthropic's remote settings, tengu_woven_ladder, contains "agent" or "mcp_tool". The list defaults to empty, and with it empty these hooks are treated as an unknown kind, as before. Nothing has been read about this list yet.
• mcp_tool hooks are kept in a separate "not connected" group, their number is capped, and their server name must match a pattern. A pattern for plugin-qualified names (plugin:<name>:...) is also added.
• A new error says mcp_tool hooks are not available for a hook event that has no MCP connection behind it, naming the event.

Before, only prompt and command hooks were read.

Why

Once enabled, hooks could start a subagent or call an MCP tool directly. If you configure an mcp_tool hook on an event that does not support it, you now get an explicit error.