The SDK control protocol gains a new file_suggestions request kind: callers can ask Claude Code's index for matching file paths and receive a list of { path } entries. This enables external tools (e.g. claude-code-vscode) to power the @ mention autocomplete from the host process.
Evidence
New SDK request branch (search for "file_suggestions" and "generateFileSuggestions").
Strings lifted out of the shipped bundle, so the claim above can be checked against them.