MCP config files are tracked, and a host can hand over a ready-made tool listing

What

MCP servers are outside programs that give Claude Code extra tools. --mcp-config is the option that loads them from JSON files or strings. Two related things changed in how this configuration is read:

• File paths: the paths of files given to --mcp-config are now kept for the whole session (flagMcpConfigFilePaths, cleared on reset). For each one that is a file, both the path and its real location on disk are collected and passed to a new registration step, which checks them against the scan of allowed folders. Before, the file was read with no path registration.
• Handed listings: a server's config can now include a handed_listing string next to its url. The parser returns these as handedListings, and startup passes them on as handedMcpListings. In headless mode, a listing (its startup handshake plus tools_list, with an at timestamp) is accepted only for a dynamic http server whose URL matches. A listing older than 600 seconds is dropped. When connecting, cached servers can now have their capabilities, server details and instructions filled from a stored handshake. What supplies this data and whether it is switched on was not traced.

Why

A program hosting Claude Code can hand over a server's tool list ahead of time, so Claude Code can skip asking the server for it, which affects how quickly tools are available at startup.