🧹 fix: Skip Numeric Splat Keys When Extracting Log Metadata

When a caller passes a primitive as the second argument — e.g.
`logger.warn('Unhandled step creation type:', step.type)` — winston /
`format.splat()` can leave character-index keys (`"0"`, `"1"`, …) on the
`info` object. With the warn/error metadata trailer in play, those
synthetic artifacts were being surfaced as bogus metadata, producing
noisy console and debug-file output.

Filter out numeric-string keys in `extractMetaObject` so only real
metadata fields reach the trailer. Added a regression test.

Reviewed-by: Codex (P2 finding on PR #12737, commit b34628de).

api/config/__tests__/parsers.spec.js

@@ -43,6 +43,20 @@ describe('formatConsoleMeta', () => {
     expect(meta).toBe('{"userField":"keep"}');
   });
 
+  it('drops numeric-index-like keys (splat artifacts from primitive args)', () => {
+    const meta = formatConsoleMeta({
+      level: 'warn',
+      message: 'Unhandled step:',
+      timestamp: 'ts',
+      0: 'f',
+      1: 'o',
+      2: 'o',
+      realField: 'real',
+    });
+
+    expect(meta).toBe('{"realField":"real"}');
+  });
+
   it('drops empty, null, undefined, function, and symbol values', () => {
     const meta = formatConsoleMeta({
       level: 'warn',

api/config/parsers.js

@@ -110,6 +110,16 @@ function extractMetaObject(source) {
     if (RESERVED_LOG_KEYS.has(key) || key.startsWith('_')) {
       continue;
     }
+    /*
+     * Skip numeric-index-like keys. When a caller passes a primitive as
+     * the second argument to `logger.warn/error`, `format.splat()` can
+     * leave character-index keys ("0", "1", ...) on `info`. Those are
+     * synthetic splat artifacts, not real metadata, and would otherwise
+     * produce noisy output now that warn/error share this path.
+     */
+    if (/^\d+$/.test(key)) {
+      continue;
+    }
     const value = source[key];
     if (value === undefined || value === null || value === '') {
       continue;