feat(scheduler): rotate equivalent candidates across dates

app/scheduler.py

@@ -1,3 +1,5 @@
+from datetime import date
+
 from app.constants import RiskLevel
 from app.models import Employee, EmployeeProfile, Shift
 from app.personalized_workload import calculate_personalized_workload_score
@@ -26,6 +28,20 @@ def assign_shifts(
     for shift in sorted_shifts:
         eligible = [e for e in employees if e.can_take_shift(shift)]
 
+        # Rotate only the final tie-breaker: risk, workload, preferences and
+        # skill flexibility always take precedence. This avoids repeatedly
+        # picking the first alphabetical name for otherwise equal shifts.
+        names_in_order = sorted(eligible, key=lambda e: (e.name.casefold(), e.name))
+        start_index = (
+            (date.fromisoformat(shift.date) - date(1970, 1, 1)).days
+            % len(names_in_order)
+            if names_in_order else 0
+        )
+        rotating_rank = {
+            id(employee): (index - start_index) % len(names_in_order)
+            for index, employee in enumerate(names_in_order)
+        }
+
         def sort_key(e: Employee):
             profile = profiles_by_name.get(e.name)
 
@@ -46,8 +62,7 @@ def sort_key(e: Employee):
                 personalized_score,
                 e.total_workload_score,
                 len(e.skills),
-                e.name.casefold(),
-                e.name,
+                rotating_rank[id(e)],
             )
 
         sorted_employees = sorted(eligible, key=sort_key)

tests/test_scheduler.py

@@ -193,8 +193,7 @@ def chosen_name(order):
         assign_shifts(employees, [shift])
         return shift.assigned_employees[0].name
 
-    assert chosen_name(["Zoe", "Anna"]) == "Anna"
-    assert chosen_name(["Anna", "Zoe"]) == "Anna"
+    assert chosen_name(["Zoe", "Anna"]) == chosen_name(["Anna", "Zoe"])
 
 
 def test_equal_assignment_count_prefers_lower_total_workload():
@@ -216,3 +215,26 @@ def test_equal_assignment_count_prefers_lower_total_workload():
     )
 
     assert next_shift.assigned_employees == [lightly_loaded]
+
+
+def test_equal_priority_ties_rotate_across_consecutive_days():
+    def assigned_name(day):
+        employees = [Employee("Anna", 5, ["CT"]), Employee("Zoe", 5, ["CT"])]
+        shift = Shift(day, ShiftType.DAY, "CT")
+        assign_shifts(employees, [shift])
+        return shift.assigned_employees[0].name
+
+    monday = assigned_name("2026-05-11")
+    tuesday = assigned_name("2026-05-12")
+
+    assert {monday, tuesday} == {"Anna", "Zoe"}
+
+
+def test_rotation_does_not_override_skill_requirements():
+    anna = Employee("Anna", 4, ["MR"])
+    zoe = Employee("Zoe", 4, ["CT"])
+    shift = Shift("2026-05-12", ShiftType.DAY, "CT")
+
+    assign_shifts([anna, zoe], [shift])
+
+    assert shift.assigned_employees == [zoe]