Function collect_input 

pub fn collect_input(
    stdin_flag: Option<&str>,
    cli_kwargs: HashMap<String, Value>,
    large_input: bool,
) -> Result<HashMap<String, Value>, CliError>

Merge CLI keyword arguments with optional JSON input.

Resolution order (highest priority first):

1. CLI flags (non-Null values in cli_kwargs)
2. JSON from stdin_flag:
   • Some("-") → read from stdin
   • Some(path) → read from file at path
   • None → no JSON input, return CLI kwargs only

Arguments

• stdin_flag — Some("-") for stdin, Some(path) for a file, None to skip
• cli_kwargs — map of flag name → value (Null values are ignored)
• large_input — if false, reject payloads exceeding 10 MiB

Errors

Returns CliError (exit code 2) on oversized input, invalid JSON, non-object JSON, or file open failures.