Refactor: Extract shared column validation logic into helper function

[codekiln]

Summary

The column validation logic for --columns and --show-columns flags is duplicated across three commands:

• assistant list (cli/src/commands/assistant.rs:219-242)
• deployment list (cli/src/commands/deployment.rs:224-245)
• model-config list (cli/src/commands/model_config.rs:172-193)

Proposed Solution

Extract this pattern into a shared helper function in cli/src/output.rs:

pub fn validate_and_show_columns(
    columns: &Option<Vec<String>>,
    show_columns: bool,
    available_columns: &[&str],
    command_name: &str,
) -> Result<()> {
    if show_columns {
        println!("Available columns for {} list:", command_name);
        for col in available_columns {
            println!("  {}", col);
        }
        println!("\nUsage: langstar {} list -f text --columns <col1,col2>", command_name);
        return Ok(());
    }

    if let Some(cols) = columns {
        for col in cols {
            if !available_columns.contains(&col.as_str()) {
                return Err(CliError::Config(format!(
                    "Invalid column '{}'. Available columns: {}",
                    col,
                    available_columns.join(", ")
                )));
            }
        }
    }
    Ok(())
}

Related

• Raised in PR ✨ feat(cli): add text output support for assistant, deployment, and model-config list #692 review: ✨ feat(cli): add text output support for assistant, deployment, and model-config list #692 (comment)
• Part of text output rollout (529.2-cli-output-implementation Implement text output format and column selection for AI-friendly CLI #584)

Benefits

• Reduces code duplication
• Improves maintainability
• Makes it easier to add consistent behavior across commands