fix(ers): lazily register database/sql driver in SQL ERS provider

service/entityresolution/multi-strategy/providers/sql/sql_provider.go

@@ -5,15 +5,57 @@
 	"database/sql"
 	"fmt"
 	"strings"
+	"sync"
 
-	// Database drivers would be imported here:
-	// _ "github.com/lib/pq"           // PostgreSQL driver
-	// _ "github.com/go-sql-driver/mysql" // MySQL driver
-	// _ "github.com/mattn/go-sqlite3" // SQLite driver
-
+	"github.com/jackc/pgx/v5/stdlib"
 	"github.com/opentdf/platform/service/entityresolution/multi-strategy/types"
 )
 
+var (
+	// driverRegMu guards lazy driver registration to prevent duplicate-register panics.
+	driverRegMu       sync.Mutex
+	registeredDrivers = make(map[string]struct{})
+)
+
+// ensureDriverRegistered lazily registers the named database/sql driver the first
+// time a SQL provider for that driver is created. This avoids the need for
+// consumers to add blank driver imports to their own binaries.
+//
+// Uses pgx/v5/stdlib for postgres (already a platform dependency). Other drivers
+// (mysql, sqlite) are not currently auto-registered and must be imported by the
+// consumer. Consumers that have already registered the driver themselves are
+// handled gracefully via a sql.Drivers() pre-check.
+func ensureDriverRegistered(driver string) {
+	// Normalize to lowercase so "Postgres", "POSTGRES", and "postgres" all resolve
+	// to the same registered driver name. sql.Register is case-sensitive.
+	driver = strings.ToLower(strings.TrimSpace(driver))
+
+	driverRegMu.Lock()
+	defer driverRegMu.Unlock()
+
+	if _, ok := registeredDrivers[driver]; ok {
+		return
+	}
+
+	// Check whether the driver was already registered externally (e.g. via a
+	// blank import in the consumer binary) before attempting to register it.
+	// Use strings.EqualFold so the pre-check is also case-insensitive.
+	for _, d := range sql.Drivers() {
+		if strings.EqualFold(d, driver) {
+			registeredDrivers[driver] = struct{}{}
+			return
+		}
+	}
+
+	switch driver {
+	case "postgres":
+		sql.Register("postgres", stdlib.GetDefaultDriver())
+		registeredDrivers[driver] = struct{}{}
+	}
+	// mysql and sqlite require imports not present in this module's dependencies.
+	// Add cases here when those drivers are added to go.mod.
+}
+
 // Provider implements the Provider interface for SQL databases
 type Provider struct {
 	name   string
@@ -24,6 +66,15 @@
 
 // NewProvider creates a new SQL provider
 func NewProvider(ctx context.Context, name string, config Config) (*Provider, error) {
+	// Normalize the driver name so "Postgres", "POSTGRES", and "postgres" all
+	// resolve correctly through ensureDriverRegistered and sql.Open, both of
+	// which use case-sensitive driver name matching.
+	config.Driver = strings.ToLower(strings.TrimSpace(config.Driver))
+
+	// Register the database/sql driver for this provider's configured driver name
+	// if it has not already been registered.
+	ensureDriverRegistered(config.Driver)
+
 	provider := &Provider{
 		name:   name,
 		config: config,