test(rag): add rag-v3 dispatch integration test + refresh stale rag-v2 docs (code-review)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

crates/kebab-rag/src/pipeline.rs

@@ -11,8 +11,8 @@
 //!    until the `max_context_tokens` budget is exhausted (estimated at
 //!    ~4 chars / token, matching the kb-chunk convention).
 //! 4. Render the configured `prompt_template_version` prompt (system +
-//!    user) verbatim per design — `rag-v1` legacy or `rag-v2` (default,
+//!    user) verbatim per design — `rag-v3` (default), `rag-v1`/`rag-v2`
-//!    fb-40) selected via `system_prompt_for`.
+//!    legacy, selected via `system_prompt_for`.
 //! 5. Generate via `LanguageModel::generate_stream`. The token loop runs
 //!    on the calling thread; `opts.stream_sink` (if any) emits
 //!    `StreamEvent::RetrievalDone` once after retrieve+stale-stamp,

crates/kebab-rag/tests/pipeline.rs

@@ -675,7 +675,7 @@ fn ask_with_multi_hop_false_keeps_single_pass_path() {
     assert_eq!(
         answer.prompt_template_version.0,
         // Single-pass stamps the config's prompt_template_version
-        // (config default = "rag-v2"), NOT "rag-multi-hop-v1".
+        // (config default = "rag-v3"), NOT "rag-multi-hop-v1".
         env.config.rag.prompt_template_version,
         "multi_hop=false must keep the config's prompt template (single-pass)"
     );

crates/kebab-rag/tests/prompt_template_dispatch.rs

@@ -151,6 +151,29 @@ fn ask_with_rag_v2_uses_v2_system_prompt() {
     );
 }
 
+#[test]
+fn ask_with_rag_v3_uses_v3_system_prompt() {
+    let (pipeline, captured, _env) = build_pipeline_with_template("rag-v3");
+    let _ = pipeline.ask("hello", lexical_opts());
+    let s = captured
+        .lock()
+        .unwrap()
+        .clone()
+        .expect("system prompt captured");
+    assert!(
+        s.contains("로컬 KB 위에서 동작"),
+        "shared prefix expected, got: {s}"
+    );
+    assert!(
+        s.contains("학습 지식"),
+        "V3 must contain 학습 지식 rule, got: {s}"
+    );
+    assert!(
+        s.contains("원본 질문"),
+        "V3 must contain language-matching rule (v3-only), got: {s}"
+    );
+}
+
 #[test]
 fn ask_with_unknown_template_returns_early_error() {
     let (pipeline, _captured, _env) = build_pipeline_with_template("rag-v99");