Struct Selection 

pub struct Selection {
    pub candidates: BTreeMap<String, Candidate>,
    pub unresolved: Vec<(String, String)>,
    pub diagnostics: Vec<Diagnostic>,
}

The candidates a request reaches, and everything the walk learned on the way.

Keyed by canonical identifier, which is what makes structural deduplication a property of the type rather than a step: one identifier cannot be in here twice, so the question “was this reached more than once” is answered by a candidate’s discovered_by and never by scanning for duplicates.

The other two fields are what the walk could not do, and neither is an error. unresolved is a name the layer declares and this repository holds nothing under — a dangling reference, which is a fact about the repository worth reporting. diagnostics is what could not be read. The budget turns both into rows of the answer rather than swallowing them.

use std::collections::BTreeMap;

use majordomus_cli::devcontext::select::{Candidate, Selection};
use majordomus_cli::devcontext::{Discovery, Selector, Tier};

let uri = "majordomus://adr/0052";
let candidate = Candidate {
    uri: uri.into(),
    kind: "adr".into(),
    title: None,
    tier: Tier::Decision,
    relevance: 0.8,
    depth: 1,
    discovered_by: vec![Discovery {
        selector: Selector::Relation,
        reason: "the decision in force over this scope".into(),
        via: Some("majordomus://issue/I0301".into()),
        edge: Some("governed_by".into()),
        depth: 1,
        confidence: 1.0,
        weight: 0.9,
    }],
    object: None,
    path: None,
    status: None,
    facts: BTreeMap::new(),
};

let selection = Selection {
    candidates: BTreeMap::from([(uri.to_string(), candidate)]),
    // a reference the layer declares and nothing answers: reported, not dropped
    unresolved: vec![("majordomus://rule/gone@1".into(), "depends_on".into())],
    diagnostics: Vec::new(),
};

// the identifier is the key, so one thing is one entry however many paths found it
assert_eq!(selection.candidates.len(), 1);
assert_eq!(selection.candidates[uri].discovered_by.len(), 1);
assert!(selection.candidates.contains_key(uri));

// and a dangling reference survives to be reported as one
assert_eq!(selection.unresolved[0].0, "majordomus://rule/gone@1");

Fields

candidates: BTreeMap<String, Candidate>

By canonical identifier.

unresolved: Vec<(String, String)>

Names the layer declares that resolve to nothing this repository holds.

diagnostics: Vec<Diagnostic>

What could not be read, never an error.