Function embedding_dim 

pub fn embedding_dim() -> usize

Resolves the active embedding dimensionality (single source of truth).

Precedence:

1. SQLITE_GRAPHRAG_EMBEDDING_DIM env var (also set by the global --embedding-dim flag before dispatch);
2. the value recorded via set_active_embedding_dim — populated from the dim key of schema_meta when the database is opened, so existing 384-dim databases keep working unchanged;
3. DEFAULT_EMBEDDING_DIM.