fix: normalise customer desired to a major.minor version

This cater for the fact that the customer desired could be a full x.y.z version e.g candidate,fast or nightly versions

Author: machi1990

backend/pkg/controllers/upgradecontrollers/control_plane_version_controller.go

@@ -279,18 +279,15 @@ func (c *controlPlaneVersionSyncer) desiredControlPlaneZVersion(
 
 	actualMinorVersion := semver.MustParse(fmt.Sprintf("%d.%d.0", actualLatestVersion.Major, actualLatestVersion.Minor))
 
-	// ParseTolerant handles both "4.19" and "4.19.0" formats (validated at API level, should never fail)
-	desiredMinorVersion := api.Must(semver.ParseTolerant(customerDesiredMinor))
-
-	if len(channelGroup) == 0 {
-		logger.Info("No channel group specified. Terminating upgrade resolution.")
-		return nil, nil
-	}
+	// ParseTolerant handles both "4.19", "4.19.0" and full versions like "4.20.15". Normalize to major.minor.0
+	// so that same-minor z-stream (e.g. 4.20.0 -> 4.20.15) is not mistaken for a y-stream upgrade.
+	parsedDesired := api.Must(semver.ParseTolerant(customerDesiredMinor))
+	desiredMinorVersion := semver.MustParse(fmt.Sprintf("%d.%d.0", parsedDesired.Major, parsedDesired.Minor))
 
 	if desiredMinorVersion.LT(actualMinorVersion) {
 		return nil, utils.TrackError(fmt.Errorf(
 			"invalid next y-stream upgrade path from %s to %s: only upgrades to the next minor version are allowed, no downgrades",
-			actualMinorVersion.String(), customerDesiredMinor,
+			actualMinorVersion.String(), desiredMinorVersion.String(),
 		))
 	}
 
@@ -299,13 +296,13 @@ func (c *controlPlaneVersionSyncer) desiredControlPlaneZVersion(
 		if desiredMinorVersion.Major != actualMinorVersion.Major {
 			return nil, utils.TrackError(fmt.Errorf(
 				"invalid next y-stream upgrade path from %s to %s: major version changes are not supported",
-				actualMinorVersion.String(), customerDesiredMinor,
+				actualMinorVersion.String(), desiredMinorVersion.String(),
 			))
 		}
 		if desiredMinorVersion.Minor != actualMinorVersion.Minor+1 {
 			return nil, utils.TrackError(fmt.Errorf(
 				"invalid next y-stream upgrade path from %s to %s: only upgrades to the next minor version are allowed, no skipping minor versions",
-				actualMinorVersion.String(), customerDesiredMinor,
+				actualMinorVersion.String(), desiredMinorVersion.String(),
 			))
 		}
 	}
@@ -319,7 +316,7 @@ func (c *controlPlaneVersionSyncer) desiredControlPlaneZVersion(
 
 	if desiredMinorVersion.Minor == actualMinorVersion.Minor+1 {
 		logger.Info("Resolving next Y-stream upgrade", "actualMinor", actualMinorVersion.String(), "activeVersions", activeVersions, "channelGroup", channelGroup,
-			"targetMinor", customerDesiredMinor)
+			"targetMinor", desiredMinorVersion.String())
 
 		latestVersion, err := c.findLatestVersionInMinor(ctx, cincinnatiClient, channelGroup, desiredMinorVersion, activeVersionList)
 		if err != nil {

backend/pkg/controllers/upgradecontrollers/control_plane_version_controller_test.go

@@ -207,6 +207,61 @@ func TestDesiredControlPlaneZVersion_ZStreamManagedUpgrade(t *testing.T) {
 			expectedVersion:      nil,
 			expectedError:        false,
 		},
+		{
+			name:                 "Z-stream upgrade - candidate channel, customer desired full version (4.20.15) normalized to same minor",
+			activeVersions:       []api.HCPClusterActiveVersion{{Version: ptr.To(semver.MustParse("4.20.10"))}},
+			customerDesiredMinor: "4.20.15",
+			channelGroup:         "candidate",
+			mockSetup: func(mc *cincinatti.MockClient) {
+				mc.EXPECT().GetUpdates(gomock.AssignableToTypeOf(context.Background()), api.Must(cincinatti.GetCincinnatiURI("candidate")), "multi", "multi", "candidate-4.20", semver.MustParse("4.20.10")).Return(
+					configv1.Release{Version: "4.20.10"},
+					[]configv1.Release{{Version: "4.20.15"}, {Version: "4.20.12"}},
+					[]configv1.ConditionalUpdate{},
+					nil,
+				)
+				// Check if next minor (4.21) exists using latest candidate (4.20.15)
+				mc.EXPECT().GetUpdates(gomock.AssignableToTypeOf(context.Background()), api.Must(cincinatti.GetCincinnatiURI("candidate")), "multi", "multi", "candidate-4.21", semver.MustParse("4.20.15")).Return(
+					configv1.Release{Version: "4.20.15"},
+					[]configv1.Release{{Version: "4.21.0"}},
+					[]configv1.ConditionalUpdate{},
+					nil,
+				)
+				// isGatewayToNextMinor(4.20.15) - has path to 4.21, so 4.20.15 is selected
+				mc.EXPECT().GetUpdates(gomock.AssignableToTypeOf(context.Background()), api.Must(cincinatti.GetCincinnatiURI("candidate")), "multi", "multi", "candidate-4.21", semver.MustParse("4.20.15")).Return(
+					configv1.Release{Version: "4.20.15"},
+					[]configv1.Release{{Version: "4.21.0"}},
+					[]configv1.ConditionalUpdate{},
+					nil,
+				)
+			},
+			expectedVersion: ptr.To(semver.MustParse("4.20.15")),
+			expectedError:   false,
+		},
+		{
+			name:                 "Z-stream upgrade - nightly channel, customer desired full version (4.19.0-0.nightly-multi-...) normalized to same minor",
+			activeVersions:       []api.HCPClusterActiveVersion{{Version: ptr.To(api.Must(semver.ParseTolerant("4.19.0-0.nightly-multi-2026-01-10-204154")))}},
+			customerDesiredMinor: "4.19.0-0.nightly-multi-2026-01-12-061259",
+			channelGroup:         "nightly",
+			mockSetup: func(mc *cincinatti.MockClient) {
+				activeVer := api.Must(semver.ParseTolerant("4.19.0-0.nightly-multi-2026-01-10-204154"))
+				latestVer := api.Must(semver.ParseTolerant("4.19.0-0.nightly-multi-2026-01-12-061259"))
+				mc.EXPECT().GetUpdates(gomock.AssignableToTypeOf(context.Background()), api.Must(cincinatti.GetCincinnatiURI("nightly")), "multi", "multi", "nightly-4.19", activeVer).Return(
+					configv1.Release{Version: "4.19.0-0.nightly-multi-2026-01-10-204154"},
+					[]configv1.Release{{Version: "4.19.0-0.nightly-multi-2026-01-12-061259"}},
+					[]configv1.ConditionalUpdate{},
+					nil,
+				)
+				// Check if next minor (4.20) exists using latest candidate - it doesn't; return latest
+				mc.EXPECT().GetUpdates(gomock.AssignableToTypeOf(context.Background()), api.Must(cincinatti.GetCincinnatiURI("nightly")), "multi", "multi", "nightly-4.20", latestVer).Return(
+					configv1.Release{},
+					nil,
+					nil,
+					&cincinnati.Error{Reason: "VersionNotFound"},
+				)
+			},
+			expectedVersion: ptr.To(api.Must(semver.ParseTolerant("4.19.0-0.nightly-multi-2026-01-12-061259"))),
+			expectedError:   false,
+		},
 	}
 
 	for _, tt := range tests {