chore(rag): PR #170 회차 1 리뷰 반영

(A) ScriptedLm doc 의 `Arc<Vec<String>>` 표기 → 실제 구현 (`Vec<String>` +
    `AtomicUsize`, 외부에서 `Arc::new(ScriptedLm::new(...))` 로 wrap)
    반영.
(B) ScriptedLm::new doc 의 미존재 `with_*` builder 언급 제거.
(C) refuse path 의 hops 보존 회귀 핀 2 건 추가 (`tests/multi_hop.rs`):
    - `multi_hop_refuse_no_chunks_preserves_hops_trace`: empty pool →
      `refuse_no_chunks(Some(hops))` → Answer.hops = Some([Decompose,
      Decide]).
    - `multi_hop_refuse_score_gate_preserves_hops_trace`: top score 0.10
      < 0.30 gate → `refuse_score_gate(Some(hops))` → 같은 shape.
    refuse_* widening + ask_multi_hop 의 forwarding wiring 이 reverting
    되면 두 test 가 회귀 잡음.
(D) test 5 의 redundant `assert_ne!(.., Some(MultiHopDecomposeFailed))`
    제거 — `assert_eq!(.., None)` 이미 함의. 메시지에 의도 통합.

검증
- `cargo test -p kebab-rag -j 1 --test multi_hop` — 7 (5+2) 모두 통과.
- `cargo clippy -p kebab-rag --all-targets -j 1 -- -D warnings` clean.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

crates/kebab-rag/tests/common/mod.rs

@@ -266,10 +266,11 @@ pub fn id32(prefix: &str) -> String {
 /// of `RagPipeline::ask_multi_hop` — each can return a different
 /// payload (`["q1","q2"]`, `[]`, `"final answer [#1]"`, etc.).
 ///
-/// Internally `Arc<Vec<String>> + AtomicUsize` so the type is
-/// `Send + Sync` and can be wrapped in `Arc<dyn LanguageModel>`.
-/// Tests can read `calls()` for an assertion on the expected LLM
-/// call count.
+/// Internally `Vec<String>` (immutable after construction) plus an
+/// `AtomicUsize` index counter, so the type is `Send + Sync` and
+/// tests wrap it in `Arc::new(ScriptedLm::new(...))` to share with
+/// the pipeline. Tests can read `calls()` for an assertion on the
+/// expected LLM call count.
 ///
 /// Exhaustion (more calls than scripted responses) panics — tests
 /// that need an "infinite" final response can supply a longer
@@ -291,8 +292,10 @@ pub struct ScriptedLm {
 impl ScriptedLm {
     /// Build a scripted LM with the default model_id/provider used by
     /// the rest of the test suite (`mock-lm` / `mock`) and the
-    /// MockLanguageModel-equivalent canned usage. Call `with_*`
-    /// builders if a test needs to override the defaults.
+    /// MockLanguageModel-equivalent canned usage. No knobs are
+    /// exposed today — every multi-hop test exercises the pipeline
+    /// flow, not the LM identity. Add builders only when a test
+    /// genuinely needs to override defaults.
     pub fn new(responses: Vec<&str>) -> Self {
         Self {
             model_id: "mock-lm".to_string(),