fix: writer/reader correctness and determinism issues

- merge: cloneTable keeps relationships; skip-tables applies to new schemas
- diff: detect schema description/owner changes
- prisma: reader no longer turns relation fields into columns, enum
  detection via declared names; writer type mapping is ordered
- typeorm writer: keep explicit SQL types that cannot be inferred
- drizzle: enum columns call the enum constant; reader resolves them
- mysql/mssql/sqlite writers: honour OutputPath, deterministic column
  and constraint order; mssql live execute covers full schema
- template: ToYAML recovers from panics; Merge nil-pointer loop
- regenerate drizzle fixtures

pkg/writers/sqlite/writer.go

@@ -44,29 +44,37 @@ func (w *Writer) WriteDatabase(db *models.Database) error {
 		return w.executeDatabaseSQL(db, dbPath)
 	}
 
-	var writer io.Writer
-	var file *os.File
-	var err error
-
-	// Use existing writer if already set (for testing)
-	if w.writer != nil {
-		writer = w.writer
-	} else if w.options.OutputPath != "" {
-		// Determine output destination
-		file, err = os.Create(w.options.OutputPath)
-		if err != nil {
-			return fmt.Errorf("failed to create output file: %w", err)
-		}
-		defer file.Close()
-		writer = file
-	} else {
-		writer = os.Stdout
+	release, err := w.openOutput()
+	if err != nil {
+		return err
 	}
+	defer release()
 
-	w.writer = writer
 	return w.writeContent(db)
 }
 
+// openOutput points w.writer at the configured destination (output file or
+// stdout) when none is set, and returns a func that releases it again so the
+// writer can be reused.
+func (w *Writer) openOutput() (func(), error) {
+	if w.writer != nil {
+		return func() {}, nil
+	}
+	if w.options.OutputPath != "" {
+		file, err := os.Create(w.options.OutputPath)
+		if err != nil {
+			return nil, fmt.Errorf("failed to create output file: %w", err)
+		}
+		w.writer = file
+		return func() {
+			file.Close()
+			w.writer = nil
+		}, nil
+	}
+	w.writer = os.Stdout
+	return func() { w.writer = nil }, nil
+}
+
 // writeContent writes the header, pragma, and every schema's DDL to w.writer.
 func (w *Writer) writeContent(db *models.Database) error {
 	// Write header comment
@@ -184,6 +192,12 @@ func tableSchemaName(schema string) string {
 
 // WriteSchema writes a single schema as SQLite SQL
 func (w *Writer) WriteSchema(schema *models.Schema) error {
+	release, err := w.openOutput()
+	if err != nil {
+		return err
+	}
+	defer release()
+
 	tableSchema := tableSchemaName(schema.Name)
 
 	if err := w.checkDirectives(schema); err != nil {
@@ -229,6 +243,11 @@ func (w *Writer) WriteSchema(schema *models.Schema) error {
 
 // WriteTable writes a single table as SQLite SQL
 func (w *Writer) WriteTable(table *models.Table) error {
+	release, err := w.openOutput()
+	if err != nil {
+		return err
+	}
+	defer release()
 	return w.writeTable("", table)
 }