---
id: "0012"
date: 2026-06-04
status: Accepted
supersedes:
superseded-by:
affected-paths: []
affected-components: []
migration_confidence: medium
migration_source: "docs/memory-system/03-architecture-decisions.md### ADR-012 — Reuse the existing SecondBrain vault as the knowledge vault"
---

# 0012 — Reuse the existing SecondBrain vault as the knowledge vault

## Context

The design called for a flat markdown vault as the semantic knowledge layer
  (ADR-003/008/010). The question was whether to stand up a new `~/brain` vault from scratch
  or adopt the existing `~/Documents/SecondBrain` vault.

## Decision

**Adopt `~/Documents/SecondBrain`** as the knowledge vault rather than
  creating a new vault.
- **Rationale**: Assessment found the SecondBrain vault is already flat (all notes at root,
  only a `_templates/` exception — exactly what the design permits), already articulates the
  correct "durable knowledge, not working memory" role in its `CLAUDE.md` and
  `vault-conventions.md`, and contains ~20 real notes. It also includes two patterns that
  **improve on the current design** and should be adopted:
  1. `vault-conventions.md`'s "act without being asked" section specifying *when* the AI
     should proactively query the vault — a behavioral spec the cc-os docs lacked.
  2. Project-config hub notes with a tag-inference table (auto-tag by path pattern) that
     operationalizes *how* to tag a note from a given project.
- **Adaptations required (migration cost)**:
  - Add `summary:` frontmatter to existing notes.
  - Migrate flat unnamespaced tags to the six-facet namespaced form (per ADR-011).
  - Add `scope/global` or `scope/project` to each note.
  - Initialize git in the vault (no `.git` exists yet — required by ADR-008's sync strategy).
  - Replace the vault's `~/.claude/scripts/vault_search.rb` reference (script does not exist)
    with `graphify query` (ADR-010).
  These are mechanical schema migrations, not structural rework.

## Consequences

The existing ~/Documents/SecondBrain vault is adopted as the knowledge vault instead of creating a new one, since it was already flat and already articulated the correct durable-knowledge role, and it contributes two design improvements (proactive-query behavior spec and a project-config tag-inference table) to be adopted. This requires mechanical migration work: adding summary frontmatter, migrating tags to the six-facet form, adding scope tags, initializing git, and replacing a nonexistent script reference with graphify query.

## Alternatives rejected

Starting fresh with a new `~/brain` vault. Rejected because the
  hardest design decision — flat structure, durable-knowledge-only role, governance philosophy
  — is already made and practiced in SecondBrain. The improved behavioral patterns
  (proactive-query spec, tag-inference table) and the existing notes are worth preserving; the
  remaining work is mechanical migration.
