fix(pgsql): strip backticks from column defaults in migration paths

Backtick-wrapped defaults (e.g. from GORM tags like `now()`) were only
stripped in the CREATE TABLE column-definition path, leaving raw
backticks in the ALTER COLUMN ... SET DEFAULT migration statement and
in the migration-generated CREATE TABLE template, producing invalid
SQL. Default-drift comparisons also compared raw values, so a
backtick-wrapped model default never matched the live DB default and
kept re-emitting redundant ALTER statements.

pkg/writers/pgsql/migration_writer.go

@@ -460,7 +460,7 @@ func (w *MigrationWriter) generateAlterTableScripts(schema *models.Schema, model
 			}
 
 			// Check default value changes
-			if fmt.Sprintf("%v", modelCol.Default) != fmt.Sprintf("%v", currentCol.Default) {
+			if !columnDefaultsEqual(modelCol.Default, currentCol.Default) {
 				setDefault, defaultVal := formatColumnDefaultSQL(modelCol)
 
 				sql, err := w.executor.ExecuteAlterColumnDefaultWithCheck(AlterColumnDefaultWithCheckData{
@@ -956,7 +956,24 @@ func columnsEqual(col1, col2 *models.Column) bool {
 	}
 	return columnTypesEqual(col1, col2) &&
 		col1.NotNull == col2.NotNull &&
-		fmt.Sprintf("%v", col1.Default) == fmt.Sprintf("%v", col2.Default)
+		columnDefaultsEqual(col1.Default, col2.Default)
+}
+
+// columnDefaultsEqual compares column defaults for drift detection, stripping
+// MySQL-style backticks (e.g. from GORM tags) so a model default of
+// "`now()`" is recognised as equal to a live default of "now()".
+func columnDefaultsEqual(default1, default2 interface{}) bool {
+	return normalizeDefaultForCompare(default1) == normalizeDefaultForCompare(default2)
+}
+
+func normalizeDefaultForCompare(value interface{}) string {
+	if value == nil {
+		return ""
+	}
+	if s, ok := value.(string); ok {
+		return strings.TrimSpace(stripBackticks(s))
+	}
+	return fmt.Sprintf("%v", value)
 }
 
 func columnTypesEqual(col1, col2 *models.Column) bool {

pkg/writers/pgsql/templates.go

@@ -530,7 +530,7 @@ func BuildCreateTableData(schemaName string, table *models.Table) CreateTableDat
 		}
 		if col.Default != nil {
 			if value, ok := col.Default.(string); ok {
-				colData.Default = writers.QuoteDefaultValue(value, col.Type)
+				colData.Default = writers.QuoteDefaultValue(stripBackticks(value), col.Type)
 			} else {
 				colData.Default = fmt.Sprintf("%v", col.Default)
 			}

pkg/writers/pgsql/writer.go

@@ -512,7 +512,7 @@ func formatColumnDefaultSQL(col *models.Column) (setDefault bool, defaultVal str
 		return false, ""
 	}
 	if value, ok := col.Default.(string); ok {
-		return true, writers.QuoteDefaultValue(value, col.Type)
+		return true, writers.QuoteDefaultValue(stripBackticks(value), col.Type)
 	}
 	return true, fmt.Sprintf("%v", col.Default)
 }

pkg/writers/pgsql/writer_test.go

@@ -1140,6 +1140,37 @@ func TestWriteSchema_EmitsGuardedAlterColumnDefaultStatements(t *testing.T) {
 	}
 }
 
+func TestWriteSchema_AlterColumnDefaultStripsBackticksFromFunctionExpression(t *testing.T) {
+	db := models.InitDatabase("testdb")
+	schema := models.InitSchema("public")
+
+	table := models.InitTable("agent_skills", "public")
+
+	updatedAtCol := models.InitColumn("updatedat", "agent_skills", "public")
+	updatedAtCol.Type = "timestamp"
+	updatedAtCol.Default = "`now()`"
+	table.Columns["updatedat"] = updatedAtCol
+
+	schema.Tables = append(schema.Tables, table)
+	db.Schemas = append(db.Schemas, schema)
+
+	var buf bytes.Buffer
+	writer := NewWriter(&writers.WriterOptions{})
+	writer.writer = &buf
+
+	if err := writer.WriteDatabase(db); err != nil {
+		t.Fatalf("WriteDatabase failed: %v", err)
+	}
+
+	output := buf.String()
+	if strings.Contains(output, "`") {
+		t.Fatalf("expected no backticks in generated SQL, got:\n%s", output)
+	}
+	if !strings.Contains(output, "ALTER COLUMN updatedat SET DEFAULT now()") {
+		t.Fatalf("expected guarded SET DEFAULT now() without backticks, got:\n%s", output)
+	}
+}
+
 func TestWriteSchema_GuardedAlterColumnTypeFallsBackOnConversionFailure(t *testing.T) {
 	db := models.InitDatabase("testdb")
 	schema := models.InitSchema("public")