fix(cron): accept weekday lists and no-'every' natural schedules (#51975)

Widens _natural_every_to_cron to consume comma/'and'-separated weekday
lists ('Monday, Wednesday at 9am' -> '0 9 * * 1,3') and applies the same
helper to schedules without the 'every' prefix, matching the exact forms
the Desktop dialog advertises in the #51975 repro.

cron/jobs.py

@@ -861,19 +861,40 @@ def _natural_every_to_cron(rest: str) -> Optional[str]:
         "monday 9am"      -> "0 9 * * 1"
         "day at 9am"      -> "0 9 * * *"
         "weekday at 9am"  -> "0 9 * * 1-5"
+        "monday, wednesday at 9am" -> "0 9 * * 1,3"
 
     Returning None lets ``parse_schedule`` fall back to the interval
     (``every 30m``) path, so existing duration schedules are unaffected.
     """
-    tokens = rest.lower().split()
+    tokens = rest.lower().replace(",", " ").split()
     if not tokens:
         return None
-    day_token = tokens[0]
-    dow = _WEEKDAY_TO_CRON_DOW.get(day_token) or _DAYSPEC_TO_CRON_DOW.get(day_token)
-    if dow is None:
-        return None
 
-    time_tokens = tokens[1:]
+    # Consume one or more leading day tokens: a keyword spec ("weekdays"),
+    # a single weekday, or a comma/"and"-separated weekday list
+    # ("monday, wednesday at 9am").
+    day_token = tokens[0]
+    dow = _DAYSPEC_TO_CRON_DOW.get(day_token)
+    idx = 1
+    if dow is None:
+        days = []
+        while idx <= len(tokens):
+            tok = tokens[idx - 1]
+            if tok == "and":
+                idx += 1
+                continue
+            mapped = _WEEKDAY_TO_CRON_DOW.get(tok)
+            if mapped is None:
+                break
+            if mapped not in days:
+                days.append(mapped)
+            idx += 1
+        if not days:
+            return None
+        dow = ",".join(days)
+        idx -= 1
+
+    time_tokens = tokens[idx:]
     # Optional "at" separator: "every day at 9am".
     if time_tokens and time_tokens[0] == "at":
         time_tokens = time_tokens[1:]

tests/cron/test_jobs.py

@@ -129,6 +129,28 @@ class TestParseSchedule:
         pytest.importorskip("croniter")
         assert parse_schedule("every weekend at 10am")["expr"] == "0 10 * * 0,6"
 
+    def test_no_every_prefix_natural_forms(self):
+        # The Desktop dialog advertises these WITHOUT the "every" prefix
+        # (#51975 repro): they must parse identically.
+        pytest.importorskip("croniter")
+        assert parse_schedule("weekdays at 9am")["expr"] == "0 9 * * 1-5"
+        assert parse_schedule("monday at 9:30")["expr"] == "30 9 * * 1"
+        assert parse_schedule("daily at 7am")["expr"] == "0 7 * * *"
+
+    def test_weekday_list_forms(self):
+        # Comma/"and"-separated day lists from the #51975 repro.
+        pytest.importorskip("croniter")
+        assert parse_schedule("Monday, Wednesday at 9am")["expr"] == "0 9 * * 1,3"
+        assert parse_schedule("monday and friday at 5pm")["expr"] == "0 17 * * 1,5"
+        assert parse_schedule("every tue, thu 8am")["expr"] == "0 8 * * 2,4"
+
+    def test_natural_form_negatives_still_reject(self):
+        pytest.importorskip("croniter")
+        with pytest.raises(ValueError):
+            parse_schedule("monday banana at 9am")
+        with pytest.raises(ValueError):
+            parse_schedule("funday at 9am")
+
     def test_every_time_formats(self):
         pytest.importorskip("croniter")
         # 24-hour, explicit minutes, noon/midnight, bare hour.