Add option to manually swap shifts after the schedule has been generated

src-tauri/tests/integration.rs

@@ -126,6 +126,36 @@ mod integration_tests {
         Ok(())
     }
 
+    #[rstest]
+    fn test_swap_preserves_constraints(
+        #[values(1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12)] month_idx: u8,
+        mut minimal_config: UserConfig,
+    ) -> anyhow::Result<()> {
+        minimal_config.update_month(month_idx);
+        let scheduler = Scheduler::new_with_config(minimal_config.clone());
+        let mut schedule = MonthlySchedule::new();
+        let mut tracker = WorkloadTracker::default();
+        assert!(scheduler.run(&mut schedule, &mut tracker)?);
+
+        let slots: Vec<_> = schedule.0.keys().copied().collect();
+        let mut swapped = false;
+        for slot in slots {
+            let candidates = schedule.possible_swaps(slot, &minimal_config);
+            if let Some(&(swap_target, _)) = candidates.first() {
+                schedule
+                    .apply_swap(slot, swap_target, &minimal_config, &mut tracker)
+                    .expect("apply_swap failed for a candidate returned by possible_swaps");
+                swapped = true;
+                break;
+            }
+        }
+
+        assert!(swapped, "No valid swap found in generated schedule");
+        validate_all_constraints(&schedule, &tracker, &minimal_config);
+
+        Ok(())
+    }
+
     #[rstest]
     fn test_export_pipeline(minimal_config: UserConfig) -> anyhow::Result<()> {
         let scheduler = Scheduler::new_with_config(minimal_config.clone());