fix(core): Fix lint error and skip surrogate tests on Node 18

Remove unnecessary type assertion to fix lint. Use describe.runIf and
it.runIf to skip surrogate replacement tests on runtimes without
toWellFormed() (Node 18).

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: antonis

packages/core/src/logs/internal.ts

@@ -254,7 +254,7 @@ function sanitizeLogAttributes(attributes: Attributes): Attributes {
 export function _INTERNAL_removeLoneSurrogates(str: string): string {
   const s = str as unknown as { isWellFormed?: () => boolean; toWellFormed?: () => string };
   if (typeof s.isWellFormed === 'function') {
-    return s.isWellFormed() ? str : (s.toWellFormed as () => string)();
+    return s.isWellFormed() ? str : s.toWellFormed ? s.toWellFormed() : str;
   }
   return str;
 }

packages/core/test/lib/logs/internal.test.ts

@@ -1267,7 +1267,10 @@ describe('_INTERNAL_captureLog', () => {
     });
   });
 
-  describe('lone surrogate sanitization', () => {
+  // toWellFormed() is only available in Node 20+, Chrome 111+, Safari 15.4+, Firefox 119+, Hermes
+  const hasToWellFormed = typeof ''.isWellFormed === 'function';
+
+  describe.runIf(hasToWellFormed)('lone surrogate sanitization', () => {
     it('sanitizes lone surrogates in log message body', () => {
       const options = getDefaultTestClientOptions({ dsn: PUBLIC_DSN, enableLogs: true });
       const client = new TestClient(options);
@@ -1362,6 +1365,9 @@ describe('_INTERNAL_captureLog', () => {
   });
 });
 
+// toWellFormed() is only available in Node 20+, Chrome 111+, Safari 15.4+, Firefox 119+, Hermes
+const hasToWellFormedGlobal = typeof ''.isWellFormed === 'function';
+
 describe('_INTERNAL_removeLoneSurrogates', () => {
   it('returns the same string when there are no surrogates', () => {
     expect(_INTERNAL_removeLoneSurrogates('hello world')).toBe('hello world');
@@ -1375,38 +1381,43 @@ describe('_INTERNAL_removeLoneSurrogates', () => {
     expect(_INTERNAL_removeLoneSurrogates('hello 😀 world')).toBe('hello 😀 world');
   });
 
-  it('replaces a lone high surrogate with U+FFFD', () => {
+  it.runIf(hasToWellFormedGlobal)('replaces a lone high surrogate with U+FFFD', () => {
     expect(_INTERNAL_removeLoneSurrogates('before\uD800after')).toBe('before\uFFFDafter');
   });
 
-  it('replaces a lone low surrogate with U+FFFD', () => {
+  it.runIf(hasToWellFormedGlobal)('replaces a lone low surrogate with U+FFFD', () => {
     expect(_INTERNAL_removeLoneSurrogates('before\uDC00after')).toBe('before\uFFFDafter');
   });
 
-  it('replaces lone high surrogate at end of string', () => {
+  it.runIf(hasToWellFormedGlobal)('replaces lone high surrogate at end of string', () => {
     expect(_INTERNAL_removeLoneSurrogates('end\uD800')).toBe('end\uFFFD');
   });
 
-  it('replaces lone low surrogate at start of string', () => {
+  it.runIf(hasToWellFormedGlobal)('replaces lone low surrogate at start of string', () => {
     expect(_INTERNAL_removeLoneSurrogates('\uDC00start')).toBe('\uFFFDstart');
   });
 
-  it('replaces multiple lone surrogates', () => {
+  it.runIf(hasToWellFormedGlobal)('replaces multiple lone surrogates', () => {
     expect(_INTERNAL_removeLoneSurrogates('\uD800\uD801\uDC00')).toBe('\uFFFD\uD801\uDC00');
   });
 
-  it('handles two consecutive lone high surrogates', () => {
+  it.runIf(hasToWellFormedGlobal)('handles two consecutive lone high surrogates', () => {
     expect(_INTERNAL_removeLoneSurrogates('\uD800\uD800')).toBe('\uFFFD\uFFFD');
   });
 
-  it('handles mixed valid pairs and lone surrogates', () => {
+  it.runIf(hasToWellFormedGlobal)('handles mixed valid pairs and lone surrogates', () => {
     expect(_INTERNAL_removeLoneSurrogates('\uD83D\uDE00\uD800')).toBe('😀\uFFFD');
   });
 
-  it('handles the exact reproduction case from issue #5186', () => {
+  it.runIf(hasToWellFormedGlobal)('handles the exact reproduction case from issue #5186', () => {
     const badValue = '{"a":"\uD800"}';
     const result = _INTERNAL_removeLoneSurrogates(badValue);
     expect(result).toBe('{"a":"\uFFFD"}');
     expect(() => JSON.parse(result)).not.toThrow();
   });
+
+  it('returns the string as-is when toWellFormed is not available', () => {
+    // Verify the function doesn't throw regardless of runtime support
+    expect(_INTERNAL_removeLoneSurrogates('normal string')).toBe('normal string');
+  });
 });