feat(format): add runtime semantic-equality safety gate

pkg/format/format_test.go

@@ -7,7 +7,6 @@ import (
 	"testing"
 
 	"git.warky.dev/wdevs/pgtidy/pkg/config"
-	"git.warky.dev/wdevs/pgtidy/pkg/lexer"
 	"git.warky.dev/wdevs/pgtidy/pkg/parser"
 )
 
@@ -199,48 +198,7 @@ func TestCorpusIdempotentAndSafe(t *testing.T) {
 	t.Logf("formatted %d corpus files (idempotent + semantically equal)", seen)
 }
 
-// semanticallyEqual compares the non-trivia token streams of two sources,
-// treating unquoted identifiers/keywords case-insensitively and everything
-// else (strings, numbers, operators, punctuation) exactly. Dollar-quoted body
-// tokens are compared recursively so body whitespace normalization does not
-// trigger a false failure.
+// semanticallyEqual is a test-local alias for the exported safety check.
 func semanticallyEqual(a, b string) bool {
-	ta := significant(a)
-	tb := significant(b)
-	if len(ta) != len(tb) {
-		return false
-	}
-	for i := range ta {
-		if ta[i].Kind != tb[i].Kind {
-			return false
-		}
-		switch ta[i].Kind {
-		case lexer.Ident:
-			if !strings.EqualFold(ta[i].Text, tb[i].Text) {
-				return false
-			}
-		case lexer.DollarString:
-			_, innerA, _, okA := splitDollarQuote(ta[i].Text)
-			_, innerB, _, okB := splitDollarQuote(tb[i].Text)
-			if okA != okB || (okA && !semanticallyEqual(innerA, innerB)) {
-				return false
-			}
-		default:
-			if ta[i].Text != tb[i].Text {
-				return false
-			}
-		}
-	}
-	return true
-}
-
-func significant(src string) []lexer.Token {
-	var out []lexer.Token
-	for _, t := range lexer.Lex(src) {
-		if t.Kind == lexer.EOF || t.IsTrivia() {
-			continue
-		}
-		out = append(out, t)
-	}
-	return out
+	return SemanticallyEqual(a, b)
 }