Responsibility map

This note records which application owns which responsibility today, and the one move still planned. Read it before proposing a refactor that crosses app boundaries.

Where responsibilities live

Responsibility	App	Status
Document metadata, MVCC, changes, replication, history	barrel_docdb	exists
Object bytes (blobs)	barrel_docdb attachments (barrel_att_backend)	exists
Vector segments, ANN, BM25, hybrid search	barrel_vectordb	exists
Embedding generation	barrel_embed	exists
Reranking	barrel_rerank	exists
Encryption at rest	barrel_crypto	exists
One id over docs + blobs + vectors, record mode, timeline	barrel	exists
Agent layer: spaces, capabilities, sessions, handoffs	barrel_spaces	exists
Transports (REST/JSON, MCP)	barrel_server	exists
Durability, placement, replication orchestration, query routing across nodes	barrel_fabric	future

Settled decisions

• Object storage is not a separate app. Blobs are barrel_docdb attachments with a pluggable backend per database (barrel_att_backend): a document owns its blob, matching how vectors and metadata attach to the same id. See ../architecture/overview.md.
• The agent layer shipped as barrel_spaces plus the MCP surface in barrel_server, not as a separate barrel_agents app.

Still planned

• barrel_fabric: dataset agents, durability, placement, replication orchestration, and query routing across nodes. Moving cross-node concerns there is its own reviewable change with its own tests, not folded into any other app.