fix(core): Resolve escape sequences in fmt / parameterize messages

`parameterize` built the message with `String.raw`, so an escape such as
`\n` or `` \` `` stayed as a backslash sequence in the log body or event
message, while the template attribute used the cooked strings. A string
with an invalid escape sequence (e.g. a Windows path) has no cooked
value, so its text dropped out of the template entirely.

Build both from the cooked strings, falling back to the raw string where
there is no cooked value.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

Author: breken-ai

packages/core/src/utils/parameterize.ts

@@ -12,8 +12,11 @@ import type { ParameterizedString } from '../types/parameterize';
  * @returns A `ParameterizedString` object that can be passed into `captureMessage` or Sentry.logger.X methods.
  */
 export function parameterize(strings: TemplateStringsArray, ...values: unknown[]): ParameterizedString {
-  const formatted = new String(String.raw(strings, ...values)) as ParameterizedString;
-  formatted.__sentry_template_string__ = strings.join('\x00').replace(/%/g, '%%').replace(/\0/g, '%s');
+  // `String.raw` would keep escape sequences such as `\n` as typed, while the template uses the cooked strings.
+  // A string with an invalid escape sequence has no cooked value, so fall back to its raw form.
+  const cooked = strings.map((str, i) => str ?? strings.raw[i]);
+  const formatted = new String(String.raw({ raw: cooked }, ...values)) as ParameterizedString;
+  formatted.__sentry_template_string__ = cooked.join('\x00').replace(/%/g, '%%').replace(/\0/g, '%s');
   formatted.__sentry_template_values__ = values;
   return formatted;
 }

packages/core/test/lib/utils/parameterize.test.ts

@@ -24,4 +24,20 @@ describe('parameterize()', () => {
     expect(formatted.__sentry_template_string__).toEqual(string.__sentry_template_string__);
     expect(formatted.__sentry_template_values__).toEqual(string.__sentry_template_values__);
   });
+
+  test('keeps escape sequences the same in the message and the template', () => {
+    const x = 'first';
+    const formatted = parameterize`Line one\nline two with ${x} → \`done\``;
+
+    expect(String(formatted)).toBe('Line one\nline two with first → `done`');
+    expect(formatted.__sentry_template_string__).toBe('Line one\nline two with %s → `done`');
+  });
+
+  test('keeps the raw text of a string with an invalid escape sequence', () => {
+    const file = 'app.log';
+    const formatted = parameterize`Reading C:\users ${file}`;
+
+    expect(String(formatted)).toBe('Reading C:\\users app.log');
+    expect(formatted.__sentry_template_string__).toBe('Reading C:\\users %s');
+  });
 });