Edit or create a file. There is no separate write or create tool in this environment — this tool does both: without `old_string` (or when `old_string` is empty) it creates a new file with `new_string` as content (refuses to overwrite an existing file); with `old_string` it replaces that text in the existing file (semi-insensitive to whitespace in code files). `path` is required on every call. `old_string` and `new_string` must differ — identical strings are rejected as a no-op. To replace every occurrence of `old_string` (more-than-one match), pass `multiple: true`.