Function auto_format 

pub fn auto_format(path: &Path, config: &Config) -> (bool, Option<String>)

Auto-format a file using the detected formatter for its language.

Returns (formatted, skip_reason):

• (true, None) — file was successfully formatted
• (false, Some(reason)) — formatting was skipped, reason explains why

Skip reasons:

• "unsupported_language" — language has no formatter support in AFT
• "no_formatter_configured" — format_on_edit=false or no formatter detected for the language in the project
• "formatter_not_installed" — configured formatter binary missing on PATH and not in project’s node_modules/.bin
• "formatter_excluded_path" — formatter ran but refused to process this path because the project formatter config (e.g. biome.json files.includes, prettier .prettierignore) excludes it. NOT an error in AFT or the user’s formatter — the user told the formatter not to touch this path. Agents should treat this as informational.
• "timeout" — formatter exceeded formatter_timeout_secs
• "error" — formatter exited non-zero with an unrecognized error (likely a real bug in the user’s input or the formatter itself)