fix(parser): validate ESC prefix byte range with correct precedence

_identifier() checked custom prefix bytes with
`res && 0x3c > res || res > 0x3f`, which parsed as
`(res && 0x3c > res) || (res > 0x3f)` because && binds tighter
than ||. A prefix of NUL (0x00) skipped both clauses and was
accepted even though only 0x3c..0x3f are valid.

Use an explicit range test: res < 0x3c || res > 0x3f. Mirror the
same fix in ApcParser and DcsParser test identifier helpers.

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

src/common/parser/ApcParser.test.ts

@@ -21,7 +21,7 @@ function identifier(id: IFunctionIdentifier): number {
       throw new Error('only one byte as prefix supported');
     }
     res = id.prefix.charCodeAt(0);
-    if (res && 0x3c > res || res > 0x3f) {
+    if (res < 0x3c || res > 0x3f) {
       throw new Error('prefix must be in range 0x3c .. 0x3f');
     }
   }

src/common/parser/DcsParser.test.ts

@@ -22,7 +22,7 @@ function identifier(id: IFunctionIdentifier): number {
       throw new Error('only one byte as prefix supported');
     }
     res = id.prefix.charCodeAt(0);
-    if (res && 0x3c > res || res > 0x3f) {
+    if (res < 0x3c || res > 0x3f) {
       throw new Error('prefix must be in range 0x3c .. 0x3f');
     }
   }

src/common/parser/EscapeSequenceParser.ts

@@ -342,7 +342,7 @@ export class EscapeSequenceParser extends Disposable implements IEscapeSequenceP
         throw new Error('only one byte as prefix supported');
       }
       res = id.prefix.charCodeAt(0);
-      if (res && 0x3c > res || res > 0x3f) {
+      if (res < 0x3c || res > 0x3f) {
         throw new Error('prefix must be in range 0x3c .. 0x3f');
       }
     }