fix: drop unconditional force-free of buffers retained for running jobs

MemoryUsageTracker freed all buffers older than the retention cutoff on
every tick whenever the last retention pass had excluded used nodes,
regardless of memory pressure — discarding the history kept in memory
for long-running jobs. Buffers are now only reclaimed by the existing
emergency path once memory usage exceeds the configured cap. The
now-unused selectorsExcluded state is removed.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

pkg/metricstore/metricstore.go

@@ -42,7 +42,6 @@ import (
 type GlobalState struct {
 	mu                sync.RWMutex
 	lastRetentionTime int64
-	selectorsExcluded bool
 }
 
 var (
@@ -440,29 +439,7 @@ func MemoryUsageTracker(wg *sync.WaitGroup, ctx context.Context) {
 				metricDataGB := ms.SizeInGB()
 				cclog.Infof("[METRICSTORE]> memory usage: %.2f GB actual (%.2f GB metric data)", actualMemoryGB, metricDataGB)
 
-				freedExcluded := 0
 				freedEmergency := 0
-				var err error
-
-				state.mu.RLock()
-				lastRetention := state.lastRetentionTime
-				selectorsExcluded := state.selectorsExcluded
-				state.mu.RUnlock()
-
-				if lastRetention != 0 && selectorsExcluded {
-					freedExcluded, err = ms.Free(nil, lastRetention)
-					if err != nil {
-						cclog.Errorf("[METRICSTORE]> error while force-freeing the excluded buffers: %s", err)
-					}
-
-					if freedExcluded > 0 {
-						debug.FreeOSMemory()
-						cclog.Infof("[METRICSTORE]> done: %d excluded buffers force-freed", freedExcluded)
-					}
-				}
-
-				runtime.ReadMemStats(&mem)
-				actualMemoryGB = float64(mem.Alloc) / 1e9
 
 				if actualMemoryGB > float64(Keys.MemoryCap) {
 					cclog.Warnf("[METRICSTORE]> memory usage %.2f GB exceeds cap %d GB, starting emergency buffer freeing", actualMemoryGB, Keys.MemoryCap)
@@ -556,13 +533,11 @@ func Free(ms *MemoryStore, t time.Time) (int, error) {
 	// If the length of the map returned by GetUsedNodes() is 0,
 	// then use default Free method with nil selector
 	case 0:
-		state.selectorsExcluded = false
 		return ms.Free(nil, t.Unix())
 
 	// Else formulate selectors, exclude those from the map
 	// and free the rest of the selectors
 	default:
-		state.selectorsExcluded = true
 		selectors := GetSelectors(ms, excludeSelectors)
 		return FreeSelected(ms, selectors, t)
 	}