Conditions and passes

ConditionType

The routing tree partitions routes on a ConditionType:

Variant	Check	Status
`SegmentCount(usize)`	number of path segments	implemented
`Length(usize)`	path string length	implemented
`Prefix(String)`	shared path prefix	planned
`Custom(Arc<dyn CustomCondition>)`	user-defined	supported

Equality is structural for the built-ins and pointer-identity for Custom.

A Pass inserts a condition level into the tree by partitioning the current routes:

impl Pass for Length {
    fn run(&mut self, tree: &mut ConditionTree) {
        tree.insert_root_condition(self, Self::partition);
    }
}

Built-in passes: Length, Segcount, and Prefix (planned). Passes are run in sequence on the tree; their order determines the tree's shape.

A custom condition implements:

trait CustomCondition {
    fn get_type(&self) -> &'static str;
    fn gen_code(&self, writer, indent, nodes) -> Result<usize, _>;
}

gen_code emits the decision code for that condition, so new routing strategies can be added without touching the core generator.