Editing documents

The document tools (read_file, edit_file, write_file, find_in_file, list_files) work over a workspace, and a workspace can be anything: a directory, memory, ActiveRecord, or one database column holding a page.

workspace = Mistri::Workspace::Single.new(
  read: -> { page.html },
  write: ->(html) { page.update!(html: html) },
  path: "hero.html",
)

agent = Mistri.agent("claude-opus-4-8",
                     tools: Mistri::Tools.files(workspace))

Now “edit the hero” is a real agent capability with no filesystem in sight.

The edit engine

edit_file matches exactly first, then whitespace-tolerantly. An ambiguous match refuses rather than silently editing the wrong place, and a near-miss error names the closest region it found, so the model’s retry is usually one-shot.