Function classify_io_error 

pub fn classify_io_error(err: &Error) -> ToolErrorCategory

Classify an io::Error into a ToolErrorCategory.

Note on io::ErrorKind::NotFound

NotFound from an Execution error means a file or binary was not found at the OS level (e.g., bash: command not found). This is NOT the same as “tool not found in registry” (ToolNotFound). We map it to PermanentFailure to avoid incorrectly penalizing the model for OS-level path issues.