Read a file, optionally from offset (1-based) for limit lines.

Returns line-numbered content like cat -n. Records the file's content hash so a subsequent edit can enforce must-read-first.

Replace old_string with new_string in file_path.

Requirements (matches opencode):

• You must call read on this file in the same session first.

• old_string must appear exactly once in the current file content. Provide more surrounding context if it isn't unique.

• The file must not have changed since the last read.

Returns a unified diff of the change.

Write content to file_path, overwriting any existing content.

Parent directories are created if missing. The file's new content hash is recorded so a follow-up edit will require a fresh read.