Design principles

The eight rules the codebase keeps to:

1. No base classes. No inheritance. No registration. No config files.
2. User code is plain functions: extract(), train(), predict().
3. Every public function has typed arguments and a typed return.
4. One name, one meaning. No overloaded types.
5. Errors tell you what to write, not what went wrong.
6. The entire public API fits on one page.
7. Each widget is a single public function, no inheritance. Implementation may be split into private _<widget>_<aspect>.py helpers (state, plot, controls) when a widget grows beyond ~200 LOC. See widgets/signal.py plus its _signal_viewer_*.py helpers for the canonical pattern. Aim to keep the public entry file under 200 lines and any single helper under ~350.
8. Immediate-mode rendering. Widget state, when needed, is keyed by widget identity and lives in a private _<widget>_state.py module.

These aren't aesthetic preferences. They're a hard contract: a library small enough to fit in one LLM context window, where every widget is a single function with no class hierarchy.