refactor: introduce store.Store graph interface with SQLite implementation

store/store.go

@@ -0,0 +1,31 @@
+package store
+
+import "axolotl/models"
+
+// Store is a primitive graph persistence interface. It provides basic
+// operations for nodes, tags, and directed edges. No business logic lives here.
+type Store interface {
+	// Nodes
+	AddNode(id, title, content, dueDate, createdAt, updatedAt string) error
+	GetNode(id string) (*models.Node, error) // returns node with tags and edges populated
+	UpdateNode(id, title, content, dueDate, updatedAt string) error // empty dueDate stores NULL
+	DeleteNode(id string) error
+	NodeExists(id string) (bool, error)
+	GenerateID() (string, error) // returns a random 5-char ID guaranteed unique in the store
+
+	// Tags
+	AddTag(nodeID, tag string) error
+	RemoveTag(nodeID, tag string) error
+
+	// Edges (directed, typed)
+	AddEdge(fromID, toID string, relType models.RelType) error
+	RemoveEdge(fromID, toID string, relType models.RelType) error
+
+	// Query returns fully-populated nodes matching all given tag prefixes and edge filters.
+	FindNodes(tagPrefixes []string, edgeFilters []*models.Rel) ([]*models.Node, error)
+
+	// Transaction runs fn inside an atomic transaction. If fn returns an error
+	// the transaction is rolled back; otherwise it is committed.
+	// Calls to Transaction inside fn reuse the same transaction (no nesting).
+	Transaction(fn func(Store) error) error
+}