cleanup: simplify detection logic and remove redundancies

- Remove redundant clusterInfo nil check in detectForDiskType since
  Detection already guards against nil clusterInfo
- Remove adjustments loop for destination servers not in
  serverVolumeCounts — topology seeding ensures all servers with
  matching disk type are already present
- Merge two-loop min/max calculation into a single loop: min across
  all servers, max only among non-exhausted servers
- Replace magic number 100 with len(metrics) for minC initialization
  in convergence test

weed/worker/tasks/balance/detection.go

@@ -81,7 +81,7 @@ func detectForDiskType(diskType string, diskMetrics []*types.VolumeHealthMetrics
 	// Seed from ActiveTopology so servers with matching disk type but zero
 	// volumes are included in the count and imbalance calculation.
 	serverVolumeCounts := make(map[string]int)
-	if clusterInfo != nil && clusterInfo.ActiveTopology != nil {
+	if clusterInfo.ActiveTopology != nil {
 		topologyInfo := clusterInfo.ActiveTopology.GetTopologyInfo()
 		if topologyInfo != nil {
 			for _, dc := range topologyInfo.DataCenterInfos {
@@ -125,14 +125,6 @@ func detectForDiskType(diskType string, diskMetrics []*types.VolumeHealthMetrics
 			effectiveCounts[server] = effective
 			totalVolumes += effective
 		}
-		// Include any destination servers not in the original disk metrics
-		for server, adj := range adjustments {
-			if _, exists := serverVolumeCounts[server]; !exists && adj > 0 {
-				effectiveCounts[server] = adj
-				totalVolumes += adj
-			}
-		}
-
 		avgVolumesPerServer := float64(totalVolumes) / float64(len(effectiveCounts))
 
 		maxVolumes := 0
@@ -141,6 +133,12 @@ func detectForDiskType(diskType string, diskMetrics []*types.VolumeHealthMetrics
 		minServer := ""
 
 		for server, count := range effectiveCounts {
+			// Min is calculated across all servers for an accurate imbalance ratio
+			if count < minVolumes {
+				minVolumes = count
+				minServer = server
+			}
+			// Max is only among non-exhausted servers since we can only move from them
 			if exhaustedServers[server] {
 				continue
 			}
@@ -148,17 +146,6 @@ func detectForDiskType(diskType string, diskMetrics []*types.VolumeHealthMetrics
 				maxVolumes = count
 				maxServer = server
 			}
-			if count < minVolumes {
-				minVolumes = count
-				minServer = server
-			}
-		}
-		// Also consider exhausted servers for minVolumes (they still exist)
-		for server, count := range effectiveCounts {
-			if count < minVolumes {
-				minVolumes = count
-				minServer = server
-			}
 		}
 
 		if maxServer == "" {

weed/worker/tasks/balance/detection_test.go

@@ -489,7 +489,7 @@ func TestDetection_ThreeServers_ConvergesToBalance(t *testing.T) {
 	// Verify convergence: effective counts should be within 20% imbalance.
 	effective := computeEffectiveCounts(servers, metrics, tasks)
 	total := 0
-	maxC, minC := 0, 100
+	maxC, minC := 0, len(metrics)
 	for _, c := range effective {
 		total += c
 		if c > maxC {