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Layer 5 — Vector Database (Qdrant)

Service: Qdrant 1.17+ (Docker) Collection: knowledge_base (4096d Cosine + BM25 sparse) Embedding: Qwen3-Embedding-8B via OpenRouter (default; configurable) Endpoint: http://localhost:6333

Why Qwen3-Embedding-8B

The default embedding model is Qwen3-Embedding-8B for four reasons:

Multilingual — strong performance across 50+ languages, including Portuguese, Spanish, and other non-English content common in real-world agent use
Quality — 4096-dimensional embeddings with high semantic fidelity; consistently ranks near the top of the MTEB leaderboard
Speed — fast inference at 8B parameters, suitable for hourly ingestion pipelines without bottlenecking the ARQ worker
Cost — affordable via OpenRouter ($0.025/1M tokens at time of writing); a full wiki re-index costs cents, not dollars

Users can switch to any OpenAI-compatible embedding API by setting EMBEDDING_API_BASE and EMBEDDING_MODEL in .env. If changing models, ensure EMBEDDING_DIMS matches both the new model's output and the Qdrant collection schema.

What it stores

All knowledge that benefits from semantic search — wiki pages, session transcripts, raw documents, technical references. Content is ingested via the continuous ingest pipeline (hourly) and the wiki agent (scheduled).

How the agent uses it

Two access patterns:

Explicit — qdrant_search(query="memory architecture", top_k=3) → agent calls the tool directly
Automatic — Icarus pre_llm_call injects relevant Qdrant results into the system prompt every turn (via _search_qdrant())

Search uses 4-level fallback cascade:

1. Hybrid: dense (4096d cosine) + sparse (BM25) → RRF fusion
2. Dense-only: if sparse fails → pure vector search
3. Lexical: if Qdrant offline → markdown file search in vault
4. SQLite: if vault inaccessible → keyword search in lineage table
5. None: all exhausted → return empty (fail-open)

Collection schema

{
  "vectors": {
    "dense": { "size": 4096, "distance": "Cosine" }
  },
  "sparse_vectors": {
    "sparse": { "index": { "on_disk": false } }
  }
}

Named vectors: Points must use {"dense": [...], "sparse": SparseVector(...)}. Must match schema exactly — unnamed vectors are rejected silently.

Decay and dedup

Mechanism	Schedule	What it does
Decay scanner	Weekly	Archives AI-generated points with low importance and high age. Exempts human-generated content and high-importance (>0.7) points. Formula: `decay_score = exp(-ln(2) * age_days / half_life)`
Semantic dedup	Monthly	Merges near-duplicate points (cosine > 0.92). Tags union, priority by source_type.

Context injection (Icarus enhancement)

_search_qdrant(query, top_k=2, threshold=0.55):
    1. Embed user message via context_enhancer pipeline
    2. search_with_fallback() → 4-level cascade
    3. Results labeled [qdrant] in system prompt
    4. Per-session dedup by point ID

Key injection pitfall: context_enhancer.py reads OPENROUTER_API_KEY (singular), but some environments use split keys. Before importing, inject: os.environ["OPENROUTER_API_KEY"] = resolved_key.

Social closer gate: Trivial messages ("ok", "thanks", emoji-only) skip Qdrant search entirely — no point embedding small talk.

Embedding pipeline

File in $VAULT_PATH/wiki/
    │
    ▼
wiki-continuous-ingest (hourly cron)
    │ SHA-256 diff detection
    ▼
Redis queue (ARQ job)
    │
    ▼
ARQ Worker (Docker)
    │ embed via configured backend (default: Qwen3-Embedding-8B)
    │ get_sparse_embedding() → BM25 (fastembed, local)
    ▼
Qdrant upsert (with dedup check)

Pitfalls

Named vectors are mandatory in Qdrant 1.17+: upsert requires "vector": {"dense": vec}, plain vectors are rejected silently
AsyncQdrantClient.search() doesn't exist in qdrant-client 1.18: Use REST API POST /collections/{name}/points/search
Embedding dimension mismatch is silent: If env says 1024 but collection is 4096, OpenRouter truncates via Matryoshka — vectors are valid but degraded
Decay scanner is inert without payload metadata: Requires importance_score, last_accessed_at, confidence_score in point payloads. Missing → all points get decay_score=1.0 → nothing archived
Isolate persona/relational collections from decay/dedup — they preserve temporal variation

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