Read the UTF-8 text content of a single file from managed workspace. Returns file content as a string.

Use this sparingly. Preferred use is very small text notes/snippets where reading the raw text is directly required.

Do NOT use read_file before sending files to the user. If user wants the file delivered, use filesystem action=send directly.

Do NOT use this for large files, binary files, or general inspection workflows. For images/documents to analyze in context, use self_insert_artifact. For metadata checks, use filesystem action=info.

Large files are truncated at 128 KB; response includes truncated=true when truncation happens.
