A command line tool usually knows all of its commands. The main class lists them, and adding a command means changing the tool. That is right for a tool with one purpose and one team. A platform is different: its capabilities come from modules written by different people and released at different times, and its command line should be the sum of the modules it runs with.

This book describes the cli module of the Nasdanika SDK Runtime, which builds a picocli command tree from whatever modules are on the module path. Nothing lists all the commands. Add a module and its commands appear; remove it and they are gone, with no other change.

Placed by type

The harder question is where each command goes. A command that saves a model needs a parent that can give it model objects; it does not care whether they come from a file, a Draw.io diagram or a database. So it says so, with generic types, and the runtime places it under every parent that can provide what it needs, before anything runs. Supplier<String> and Supplier<EObject> are one class at run time, but here they are two different contracts, matched the way the Java compiler matches them.

• Commands and factories contributed as capabilities, through the module descriptor.
• Wiring by type: what a command needs from its parent, what it asks for lazily, and what it accepts as sub-commands.
• Mix-ins contributed and matched by type, and overriding commands by subclassing or by declaration.
• The runtime's own commands, shell, distributions and launcher.

Commands placed by what they need form pipelines that read as sentences: load a diagram, turn it into a model, generate a site, each word from a module that knows nothing of the others. The last part shows the pipelines being rebuilt on this foundation.

Built on picocli, not beside it

picocli does argument parsing, help and completion superbly, and the runtime does not redo any of it. Commands are written with picocli's annotations; what this module adds is assembly by type.

Who it is for

• Java developers who build command line tools that grow by modules.
• Developers contributing commands to a modular platform.
• Architects who want a command line as the first user interface of a platform, for people, build pipelines and AI agents. The first part needs no code.

How it keeps you honest

Every listing is included from the module's sources or tests and runs when the book is built. Status labels mark what is PLANNED and what is a SKETCH.

This is a Nasdanika Zephyr Book, an in-depth manual for one module of the Nasdanika SDK Runtime, and it stands on its own. The code needs Java 25, and some familiarity with picocli helps. The text is licensed under CC BY 4.0 and the code under EPL-2.0.