depiedencap-rag — Discourse-embedded RAG agent

📘 Ce projet est également disponible en français 🇫🇷

⚠️ Work in progress. The agent is currently being tested on a restricted demo group and is not publicly deployed on the forum. This repository documents the work — no demo URL is published.

A Discourse plugin + a self-hosted RAG pipeline, built for a French community forum (Depiedencap — men's shoes, 424 835 posts / 22 230 topics). Product principle: the bot points members to existing threads instead of answering in their place.

What it does

• Post-grain retrieval (not topic-grain): bge-m3 embeddings in ai_posts_embeddings (pgvector inside the forum's Postgres on the VPS), top-25 by cosine then cross-encoder rerank (TEI on the mini PC), per-thread dedup.
• Multi-turn query rewriting: the latest message plus earlier turns are condensed into a standalone query (condense question / history-aware retriever). Same resident model as generation: qwen3:30b-a3b-q6k (MoE, ~3B active, think:false) — not a separate small rewriter.
• Server-side verified citations: the LLM only emits bare [[n]] markers; the plugin maps them to /t/slug/id/post_number links and discards any link that does not actually exist in Postgres (URL whitelist — the LLM never gets the last word on a link).
• Graduated evidence zones (abstain / cautious / normal) driven by reranker score + a deterministic input gate (intent regexes) for dangerous or out-of-role requests — zero LLM calls.
• Graceful degradation: embedding or reranker endpoint down → legacy fallback / honest abstention, never invention.

Architecture

The plugin runs inside Discourse on the VPS. The mini PC is only the inference backend (Ollama + TEI), reached over Tailscale. Gate, pgvector and the citation sanitizer never leave the VPS.

Member question
        │
        ▼
[VPS]  Discourse + this Ruby plugin
        │
        ├─ 1. gate        regex, local, 0 LLM
        │
        ├─ 2. rewrite     ──Tailscale──►  [mini PC] Ollama  qwen3:30b-a3b-q6k
        │
        ├─ 3. embed       ──Tailscale──►  [mini PC] Ollama  bge-m3
        │
        ├─ 4. pgvector    Postgres local, 424 835 posts, cosine top-25
        │
        ├─ 5. rerank      ──Tailscale──►  [mini PC] TEI     mmarco-mMiniLMv2
        │
        ├─ 6. generate    ──Tailscale──►  [mini PC] Ollama  qwen3:30b-a3b-q6k
        │
        └─ 7. sanitizer   URL whitelist, local Postgres
                │
                ▼
          answer + /t/slug/id/post_number links

Lives on the VPS	Lives on the mini PC (k3s, iGPU)
Discourse, this plugin, Postgres/pgvector	Ollama (bge-m3 + qwen3:30b-a3b-q6k) and TEI (mmarco)

qwen3:30b-a3b-q6k is a single resident MoE (~3B active) used for both rewrite (think:false) and generation.

Deliberate choice: no RAG framework (LangChain & co.) — a linear pipeline in direct code, instrumented for evaluation. Full reasoning: docs/rag/DESIGN.md §9.

Measured results (real corpus, 812-question eval set)

Metric	Value
Hit@5 retrieval	0.97
MRR	0.89
Safety (red-team, gate, refusal, evidence injection)	20/20
Rerank overhead	~100 ms

Details: docs/rag/EVAL.md · docs/rag/SAFETY.md · docs/rag/PIPELINE.md · docs/rag/REFERENCES.md

Repository layout

Path	Content
root (plugin.rb, lib/, app/, config/)	The Discourse plugin — installable via git clone into plugins/
docs/rag/	Design, evaluation, safety, references, local dev recipe
prompts/	Production system prompt (v3.1)
tools/	Live smoke test (Discourse API)

Security & privacy

• No internal endpoint, IP or account is published (sanitised export from the private working repo + automated denylist check).
• The agent stays limited to a demo group during the observation phase; documented < 5 min rollback.
• The bot refuses dangerous, illegal or generalist requests and ignores hostile instructions found inside retrieved forum excerpts.

License

AGPL-3.0 — see LICENSE.