kebab/tasks/p9/p9-fb-15-rag-multi-turn-core.md

phase, component, task_id, title, status, depends_on, unblocks, contract_source, contract_sections, source_feedback

phase	component	task_id	title	status	depends_on	unblocks	contract_source	contract_sections	source_feedback
P9	kebab-rag + kebab-app	p9-fb-15	RAG multi-turn — history-aware prompt + token budget	completed		p9-fb-16 p9-fb-17 p9-fb-18	../../docs/superpowers/specs/2026-04-27-kebab-final-form-design.md	§7 RAG	p9-dogfooding-feedback.md item 13

p9-fb-15 — RAG multi-turn core

Goal

kebab-rag 가 conversation history (Vec<Turn>) 를 받아 prompt 빌드. token budget 안에서 retrieval k 와 history truncation 정책으로 fit.

Allowed dependencies

• 기존 kebab-rag deps.
• tiktoken-rs 또는 LLM family-specific tokenizer (gemma 토큰화). 우선 char 기반 ÷4 근사 (cheap & 의존 X).

Public surface

pub struct Turn {
    pub question: String,
    pub answer: String,
    pub citations: Vec<Citation>,
    pub ts: OffsetDateTime,
}

pub fn ask_with_history(
    cfg: &Config,
    new_question: &str,
    history: &[Turn],
    stream: Sender<RagEvent>,
) -> anyhow::Result<Answer>;

kebab-app 도 ask_with_config_and_history(cfg, q, history, stream) 추가.

Behavior contract

• prompt 구조: system_prompt + history_serialized + retrieved_chunks + new_question. 형식 (roles 또는 plain text) 는 prompt_template_version bump (rag-v1 → rag-v2).
• token budget: cfg.rag.max_context_tokens.
  • 우선순위: system + new_question 항상 포함.
  • 다음: retrieved chunks (k=cfg.search.default_k 부터, budget 초과시 k 감소).
  • 마지막: history. budget 남은 만큼 newest turn 부터 포함, 부족하면 oldest turn drop. 최소 0 turn 까지 가능.
• retrieval query: new_question + " " + last_turn.answer.first_N_chars(200) concat (cheap query expansion). LLM 기반 standalone question rewriting 은 P+.
• streaming: RagEvent::Token(s) / RagEvent::Done(answer) / RagEvent::Error(e).

Test plan

kind	description
unit	history 5 turn → token budget 초과 시 oldest 부터 drop
unit	retrieved_chunks vs history 의 priority
integration	가짜 history (Q1/A1) + new Q2 → prompt 에 Q1/A1 포함 (snapshot)

DoD

• cargo test -p kebab-rag -p kebab-app 통과
• prompt_template_version bump (rag-v2)
• HOTFIXES X (신규)
• frozen design §7 RAG 절 갱신 (multi-turn 정책)

Out of scope

• LLM 기반 question rewriting (P+)
• conversation 영속화 (p9-fb-17)
• UI (p9-fb-16, p9-fb-18)