Shell completion scripts for the dcode command line.
dcode completion <shell> prints a completion script for bash, zsh, or fish.
The candidates are read from the same argparse parser that handles real
invocations, so a new flag or subcommand appears after regenerating the script
instead of needing a second list kept in sync by hand.
Generated scripts are static: write one to a file and source it from the
shell's startup file. dcode completion -h prints the per-shell setup.
