Function build_segments 

pub fn build_segments(
    config: Option<&Config>,
    plugins: Option<(PluginRegistry, Arc<Engine>)>,
    warn: impl FnMut(&str),
) -> Vec<LineItem>

Build a segment list from an optional Config. None or a config without a [line] section uses the default order. warn receives a one-line diagnostic for each validation rule triggered (pass |_| {} to discard).

plugins carries the discovered PluginRegistry plus its shared engine. Built-in ids win on collision (the registry already rejects plugins shadowing built-ins at load time, so a plugin reaching this function can only collide with another plugin or stand alone).

Implements the validation rules in docs/specs/config.md §Validation rules: unknown ids skip with a warning, duplicates keep the first, an explicit segments = [] warns, inverted width bounds drop the override with a warning.

Single-line entry; multi-line callers should use build_lines. When this function is invoked against a layout = "multi-line" config, it returns line 1 (sorted by numbered key) and warns, rather than reading the empty [line].segments field and returning nothing. Without that fallback, embedders loading the multi-line power-user preset would silently render a blank status line.