fix(cron): sort find_latest_digest by filename not st_mtime (Closes #1767)

cron/evolution_preflight.py

@@ -174,7 +174,13 @@ def _preflight_enabled(cfg: Optional[Any] = None) -> bool:
 def find_latest_digest(
     stage: str, hermes_home: Optional[Path] = None
 ) -> Optional[Path]:
-    """Return the most recent digest file for an evolution stage, or None."""
+    """Return the most recent digest file for an evolution stage, or None.
+
+    Digest filenames follow a sortable date-encoded convention
+    (``YYYY-MM-DD.json`` / ``.md``, optionally with ``-pass<N>`` / ``-tick<N>``
+    suffixes).  Sorting by filename instead of ``st_mtime`` avoids flaky
+    results when files are touched or copied after creation (#1767).
+    """
     if stage not in _EVOLUTION_STAGES:
         return None
     ext = _EVOLUTION_STAGES[stage]
@@ -183,7 +189,7 @@ def find_latest_digest(
         return None
     candidates = sorted(
         (p for p in stage_dir.iterdir() if p.is_file() and p.suffix == ext),
-        key=lambda p: p.stat().st_mtime,
+        key=lambda p: p.name,
         reverse=True,
     )
     return candidates[0] if candidates else None

tests/cron/test_evolution_preflight.py

@@ -170,10 +170,30 @@ def test_find_latest_digest(self, tmp_path):
         new = stage_dir / "2026-06-23.json"
         old.write_text("old")
         new.write_text("new")
+        # Regression for #1767: touch() on both files resets mtimes to ~now,
+        # making mtime-based sorting ambiguous.  Filename-based sorting is
+        # stable regardless of mtime.
         old.touch()
         new.touch()
         assert ep.find_latest_digest("introspection", tmp_path) == new
 
+    def test_find_latest_digest_ignores_mtime(self, tmp_path):
+        """Even when an older digest has a newer mtime, it must not win (#1767)."""
+        import os
+        import time
+
+        stage_dir = tmp_path / "evolution" / "introspection"
+        stage_dir.mkdir(parents=True)
+        old = stage_dir / "2026-06-20.json"
+        new = stage_dir / "2026-06-23.json"
+        new.write_text("new")
+        old.write_text("old")
+        # Make the older file's mtime much newer — mtime sort would pick it.
+        ts = time.time()
+        os.utime(old, (ts + 3600, ts + 3600))
+        os.utime(new, (ts, ts))
+        assert ep.find_latest_digest("introspection", tmp_path) == new
+
     def test_load_digest_as_fallback(self, tmp_path):
         stage_dir = tmp_path / "evolution" / "analysis"
         stage_dir.mkdir(parents=True)