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Write a Rule Plug-in

Rule plug-ins let you extend validation and scoring without forking the engine.

  1. Define a validator. Implement RulePlugin in Rust and register it under a ruleset ID.
  2. Expose knobs. Serialize parameters (JSON or TOML) so configs can toggle the behavior.
  3. Wire into bindings. Export the new hook through FFI so Python/WASM/Unity/Godot can opt-in.
  4. Test it. Build fixture moves and cover failure cases in both unit tests and end-to-end demos.
no_short_words.rs
use engine::rules::{PluginContext, RuleFailure, RulePlugin};

#[derive(Default)]
pub struct NoShortWords;

impl RulePlugin for NoShortWords {
    fn validate(&self, ctx: &PluginContext) -> Result<(), RuleFailure> {
        if ctx.main_word.len() < 4 {
            return Err(RuleFailure::reject("Words must be at least four letters"));
        }
        Ok(())
    }
}