fix: harden module lifecycle and debug log setup

Export CurrentDialect(), return setup errors when debug logger is not
registered, and guard DestName logging when the module is uninitialized.

Co-authored-by: Cursor <cursoragent@cursor.com>

internal/dbxshared/logger_test.go

@@ -0,0 +1,32 @@
+package dbxshared
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+type testDialect string
+
+func (d testDialect) String() string { return string(d) }
+
+type stubLogger struct{}
+
+func (stubLogger) InitLogger() {}
+
+func TestInitLogger_UnregisteredDialect(t *testing.T) {
+	ResetLoggerRegistry()
+	t.Cleanup(ResetLoggerRegistry)
+
+	err := InitLogger(testDialect("mysql"))
+	assert.ErrorContains(t, err, "blank-import dbxm")
+}
+
+func TestInitLogger_RegisteredDialect(t *testing.T) {
+	ResetLoggerRegistry()
+	t.Cleanup(ResetLoggerRegistry)
+
+	RegisterLogger(testDialect("mysql"), stubLogger{})
+	err := InitLogger(testDialect("mysql"))
+	assert.NoError(t, err)
+}