feat: SQLite default — zero external deps to start

db.New() auto-detects backend from DSN:
- "" or "sqlite://path" or "file.db" → SQLite (default)
- "postgres://..." → PostgreSQL (production upgrade)

KV (Valkey/Redis) is optional — pass "" to skip.
No postgres, no redis required to run mpcd out of the box.
Removed pgxpool direct dependency from db package.

go.mod

@@ -17,7 +17,6 @@ require (
 	github.com/hanzoai/kv-go/v9 v9.18.0
 	github.com/hanzoai/orm v0.3.2
 	github.com/hashicorp/consul/api v1.33.7
-	github.com/jackc/pgx/v5 v5.9.1
 	github.com/luxfi/crypto v1.17.45
 	github.com/luxfi/database v1.17.44
 	github.com/luxfi/fhe v1.7.7
@@ -81,6 +80,7 @@ require (
 	github.com/holiman/uint256 v1.3.2 // indirect
 	github.com/jackc/pgpassfile v1.0.0 // indirect
 	github.com/jackc/pgservicefile v0.0.0-20240606120523-5a60cdf6a761 // indirect
+	github.com/jackc/pgx/v5 v5.9.1 // indirect
 	github.com/jackc/puddle/v2 v2.2.2 // indirect
 	github.com/klauspost/compress v1.18.5 // indirect
 	github.com/klauspost/cpuid/v2 v2.3.0 // indirect

pkg/db/db.go

@@ -1,31 +1,57 @@
 package db
 
 import (
+	"fmt"
+	"strings"
+
 	kv "github.com/hanzoai/kv-go/v9"
 	"github.com/hanzoai/orm"
 	ormdb "github.com/hanzoai/orm/db"
-	"github.com/jackc/pgx/v5/pgxpool"
 )
 
-// Database holds the ORM entity store and the KV cache/session client.
+// Database holds the ORM entity store and optional KV cache.
 type Database struct {
-	ORM  orm.DB
-	KV   kv.UniversalClient
-	pool *pgxpool.Pool // underlying pool for raw SQL fallback
+	ORM orm.DB
+	KV  kv.UniversalClient
 }
 
-// New creates a Database wired to PostgreSQL (via ORM) and Valkey/Redis (via KV).
-func New(postgresURL, kvURL string) (*Database, error) {
-	sqlDB, err := ormdb.NewSQLDB(&ormdb.SQLConfig{
-		DSN:      postgresURL,
-		MaxConns: 20,
-		MinConns: 2,
-	})
-	if err != nil {
-		return nil, err
-	}
+// New creates a Database. Detects backend from DSN:
+//   - "" or "sqlite://..." or file path → SQLite (default, zero-config)
+//   - "postgres://..." → PostgreSQL
+//
+// kvURL is optional — pass "" to skip KV cache.
+func New(dsn, kvURL string) (*Database, error) {
+	var ormInstance orm.DB
 
-	ormInstance := orm.AdaptDB(sqlDB)
+	switch {
+	case dsn == "" || strings.HasPrefix(dsn, "sqlite://") || strings.HasSuffix(dsn, ".db"):
+		// SQLite — default, zero external deps.
+		path := "mpc.db"
+		if strings.HasPrefix(dsn, "sqlite://") {
+			path = strings.TrimPrefix(dsn, "sqlite://")
+		} else if strings.HasSuffix(dsn, ".db") {
+			path = dsn
+		}
+		sqliteDB, err := ormdb.NewSQLiteDB(&ormdb.SQLiteDBConfig{Path: path})
+		if err != nil {
+			return nil, fmt.Errorf("sqlite: %w", err)
+		}
+		ormInstance = orm.AdaptDB(sqliteDB)
+
+	case strings.HasPrefix(dsn, "postgres://") || strings.HasPrefix(dsn, "postgresql://"):
+		sqlDB, err := ormdb.NewSQLDB(&ormdb.SQLConfig{
+			DSN:      dsn,
+			MaxConns: 20,
+			MinConns: 2,
+		})
+		if err != nil {
+			return nil, fmt.Errorf("postgres: %w", err)
+		}
+		ormInstance = orm.AdaptDB(sqlDB)
+
+	default:
+		return nil, fmt.Errorf("unsupported DSN: %q (use sqlite://, postgres://, or .db path)", dsn)
+	}
 
 	var kvClient kv.UniversalClient
 	if kvURL != "" {
@@ -35,18 +61,11 @@ func New(postgresURL, kvURL string) (*Database, error) {
 	}
 
 	return &Database{
-		ORM:  ormInstance,
-		KV:   kvClient,
-		pool: sqlDB.Pool(),
+		ORM: ormInstance,
+		KV:  kvClient,
 	}, nil
 }
 
-// Pool returns the underlying pgxpool.Pool for raw SQL operations.
-// Use this only for queries that have no ORM equivalent.
-func (d *Database) Pool() *pgxpool.Pool {
-	return d.pool
-}
-
 // Close releases all database resources.
 func (d *Database) Close() {
 	if d.ORM != nil {