fix: clamp ResourcePool available at zero and stop corrupting Hard

api/v1beta2/resourcepool_func.go

@@ -159,12 +159,23 @@ func (r *ResourcePool) CalculateAvailableResources() {
 	available := corev1.ResourceList{}
 
 	for res, qt := range r.Status.Allocation.Hard {
+		// Deep-copy qt before subtracting: resource.Quantity contains internal pointers,
+		// so a shallow copy can alias the map entry and Sub() could mutate Hard.
+		// Using DeepCopy() ensures Hard remains unchanged.
+		remaining := qt.DeepCopy()
+
 		amount, exists := r.Status.Allocation.Claimed[res]
 		if exists {
-			qt.Sub(amount)
+			remaining.Sub(amount)
+		}
+
+		// A pool can never offer a negative amount of resources, so clamp
+		// at zero. This also keeps Hard intact for downstream math.
+		if remaining.Sign() < 0 {
+			remaining = resource.MustParse("0")
 		}
 
-		available[res] = qt
+		available[res] = remaining
 	}
 
 	r.Status.Allocation.Available = available

api/v1beta2/resourcepool_func_test.go

@@ -164,6 +164,44 @@ func TestCalculateResources(t *testing.T) {
 	assert.Equal(t, 0, (&actualAvailable).Cmp(resource.MustParse("1")))
 }
 
+func TestCalculateResources_OverSubscriptionDoesNotGoNegative(t *testing.T) {
+	pool := &capsulev1beta2.ResourcePool{
+		Status: capsulev1beta2.ResourcePoolStatus{
+			Allocation: capsulev1beta2.ResourcePoolQuotaStatus{
+				Hard: corev1.ResourceList{
+					corev1.ResourceLimitsCPU: resource.MustParse("10"),
+				},
+			},
+			Claims: capsulev1beta2.ResourcePoolNamespaceClaimsStatus{
+				"ns": {
+					&capsulev1beta2.ResourcePoolClaimsItem{
+						Claims: corev1.ResourceList{
+							corev1.ResourceLimitsCPU: resource.MustParse("55"),
+						},
+					},
+				},
+			},
+		},
+	}
+
+	pool.CalculateClaimedResources()
+
+	// Even when claims exceed the hard limit, available must clamp at zero
+	// and Hard must stay intact (regression: subtracting in place corrupted
+	// both Hard and Available, producing negative values — see issue #1977).
+	actualAvailable := pool.Status.Allocation.Available[corev1.ResourceLimitsCPU]
+	assert.Equal(t, 0, (&actualAvailable).Cmp(resource.MustParse("0")))
+
+	actualHard := pool.Status.Allocation.Hard[corev1.ResourceLimitsCPU]
+	assert.Equal(t, 0, (&actualHard).Cmp(resource.MustParse("10")))
+
+	// With zero available, a new oversized claim must be rejected.
+	errs := pool.CanClaimFromPool(corev1.ResourceList{
+		corev1.ResourceLimitsCPU: resource.MustParse("55"),
+	})
+	assert.Len(t, errs, 1)
+}
+
 func TestCanClaimFromPool(t *testing.T) {
 	pool := &capsulev1beta2.ResourcePool{
 		Status: capsulev1beta2.ResourcePoolStatus{