Fill: plant nothing for a region that misses the object entirely

clampTo INVERTS a region lying wholly outside the object — Max clamps below
Min — rather than emptying it. The old loop-until-past-MaxX form handled that
for free by never entering the loop. Counting positions up front does not:
a region 500cm east of a bed with ±50cm local bounds produced 4 plops at
x=275, a couple of metres off the bed.

Caught by removing the guard and watching the new test fail, not by assuming
it would.

Co-Authored-By: Claude Opus 4.8 (1M context) <[email protected]>
Claude-Session: https://claude.ai/code/session_01H3zbym8Doka2d7D48maSgZ

internal/service/ops.go

@@ -195,6 +195,13 @@ func hexCenters(r Region, radius, spacing float64) []localPoint {
 	if radius <= 0 {
 		return nil
 	}
+	// clampTo INVERTS a region that lies wholly outside the object (Max clamps
+	// below Min), and an inverted region has no inside to plant. The old
+	// loop-until-past-MaxX form got this for free by never entering the loop;
+	// counting positions up front does not, and would site a plop off the bed.
+	if r.MaxX < r.MinX || r.MaxY < r.MinY {
+		return nil
+	}
 	pitch := 2 * radius
 	rowH := pitch * math.Sqrt(3) / 2
 

internal/service/ops_test.go

@@ -161,6 +161,27 @@ func TestHexCentersTinyRegion(t *testing.T) {
 	}
 }
 
+// TestFillRegionOutsideObjectPlantsNothing covers a region that misses the object
+// entirely. clampTo inverts such a region rather than emptying it, and an
+// inverted region must plant nothing — not one plop at some point off the bed.
+func TestFillRegionOutsideObjectPlantsNothing(t *testing.T) {
+	ctx := context.Background()
+	s := newTestService(t, openConfig())
+	owner := seedUser(t, s, "[email protected]")
+	g, _ := s.CreateGarden(ctx, owner, GardenInput{Name: "Big", WidthCM: 2000, HeightCM: 2000})
+	bed := seedFillBed(t, s, owner, g.ID, 100, 100) // local bounds ±50
+	plant := seedOwnPlant(t, s, owner, 10)
+
+	// Wholly east of the bed: clampTo gives MinX=500, MaxX=50.
+	created, err := s.FillRegion(ctx, owner, bed.ID, rect(500, -50, 600, 50), plant.ID, nil)
+	if err != nil {
+		t.Fatalf("FillRegion: %v", err)
+	}
+	if len(created) != 0 {
+		t.Errorf("filled %d plops for a region outside the bed, want 0: %+v", len(created), created)
+	}
+}
+
 // seedFillBed makes a plantable bed of the given size centered in a big garden.
 func seedFillBed(t *testing.T, s *Service, owner, gardenID int64, w, h float64) *domain.GardenObject {
 	t.Helper()