ADR-0002: In-memory networkx graph first; Neo4j as an optional mirror

Status: Accepted

Context

The spec targets Neo4j. However, requiring a database server makes tests, CI and demos heavier, and at MVP scale (thousands of nodes) Neo4j is not needed.

Decision

The reference store is a networkx.MultiDiGraph, where the edge key is the predicate. neo4j_adapter generates parameterized Cypher and can push to a local Neo4j when the driver is installed.

Consequences

• Zero-infrastructure make test and make demo, and CI needs no services.
• The graph is not persistent and does not scale past memory. Moving to Neo4j as the primary store is a Stage 2+ decision.
• Traversals (root cause, blast radius) are written in Python for now. They will need Cypher equivalents later.