feat: P0-1e expand handleConfigPush with host config and cluster dispatch

Wires the remaining cluster_config_t data into the notification pipeline:
- dispatchConfigPush() extracted as a pure-Go helper (CGO-free, testable)
  that drives OnQueueUpdated, OnResourceUpdated, OnHostConfigUpdated, and
  OnClusterUpdated from a single config push event
- handleConfigPush() delegates to dispatchConfigPush via the new helper,
  eliminating the previous inline loops
- OnHostConfigUpdated and OnClusterUpdated added to NotificationHandler
  interface and implemented with partial-merge semantics in DefaultHandler
- rawHostConfigData/rawHostConfigToModel and rawClusterData/rawClusterToModel
  added to convert_pure.go with their CGO extraction counterparts in convert.go

Safety fixes from code review:
- OnHostUpdated, OnHostConfigUpdated, OnClusterUpdated now copy *incoming to
  a local merged value before mutation, closing the TOCTOU window between
  store.Get and store.Put under concurrent pushes
- cClusterConfQueues and cClusterConfResources gain nil-pointer guards
  matching the existing guard in cClusterConfHostConfigs
- handleConfigPush gains an explicit gHandler nil check
- cClusterConfToClusterInfo returns nil on empty clustername (prevents phantom
  empty-key write to store.Clusters); handleConfigPush logs a warning when nil
- 36 unit tests passing (CGO_ENABLED=0)

src/frontend/apiserver/backend/handler.go

@@ -24,8 +24,66 @@ func (h *DefaultHandler) OnQueueUpdated(queue *models.QueueInfo) {
 	store.Queues.Put(queue.QueueName, *queue)
 }
 
-func (h *DefaultHandler) OnHostUpdated(host *models.HostInfo) {
-	store.Hosts.Put(host.HostName, *host)
+// OnHostUpdated merges worker-sourced fields into an existing host entry.
+// Config-sourced fields (HostModel, HostType, MaxSlot, DisptWindow) are
+// preserved from the prior entry if one exists.
+func (h *DefaultHandler) OnHostUpdated(incoming *models.HostInfo) {
+	merged := *incoming
+	if existing, ok := store.Hosts.Get(merged.HostName); ok {
+		merged.HostModel = existing.HostModel
+		merged.HostType = existing.HostType
+		merged.MaxSlot = existing.MaxSlot
+		merged.DisptWindow = existing.DisptWindow
+	}
+	store.Hosts.Put(merged.HostName, merged)
+}
+
+// OnHostConfigUpdated merges config-sourced fields into an existing host entry.
+// Worker-sourced fields (HostStatus, CPUFactor, NumCPUs, MaxMem, MaxSwap,
+// MaxTmp, NumDisk, NumRun, NumSSusp, NumUSusp, NumDone) are preserved from
+// the prior entry if one exists.
+// NumCores, NumThreads, Topology, SchedStop are preserved here but currently
+// have no write path in rawWorkerData — they remain zero until a future worker
+// push source populates them (analogous to the DisptWindow deferral).
+func (h *DefaultHandler) OnHostConfigUpdated(incoming *models.HostInfo) {
+	merged := *incoming
+	if existing, ok := store.Hosts.Get(merged.HostName); ok {
+		merged.HostStatus = existing.HostStatus
+		merged.CPUFactor = existing.CPUFactor
+		merged.NumCPUs = existing.NumCPUs
+		merged.NumCores = existing.NumCores
+		merged.NumThreads = existing.NumThreads
+		merged.MaxMem = existing.MaxMem
+		merged.MaxSwap = existing.MaxSwap
+		merged.MaxTmp = existing.MaxTmp
+		merged.NumDisk = existing.NumDisk
+		merged.NumRun = existing.NumRun
+		merged.NumSSusp = existing.NumSSusp
+		merged.NumUSusp = existing.NumUSusp
+		merged.NumDone = existing.NumDone
+		merged.Topology = existing.Topology
+		merged.SchedStop = existing.SchedStop
+	}
+	store.Hosts.Put(merged.HostName, merged)
+}
+
+// OnClusterUpdated merges config-sourced fields into an existing cluster entry.
+// Built-in fields (Version, Status, ControllerName, NumServers, Resources,
+// HostTypes, HostModels, ClusterAdmins) are preserved from the prior entry
+// if one exists.
+func (h *DefaultHandler) OnClusterUpdated(incoming *models.ClusterInfo) {
+	merged := *incoming
+	if existing, ok := store.Clusters.Get(merged.ClusterName); ok {
+		merged.Version = existing.Version
+		merged.Status = existing.Status
+		merged.ControllerName = existing.ControllerName
+		merged.NumServers = existing.NumServers
+		merged.Resources = existing.Resources
+		merged.HostTypes = existing.HostTypes
+		merged.HostModels = existing.HostModels
+		merged.ClusterAdmins = existing.ClusterAdmins
+	}
+	store.Clusters.Put(merged.ClusterName, merged)
 }
 
 func (h *DefaultHandler) OnResourceUpdated(res *models.ResourceDefinitionInfo) {
@@ -36,3 +94,25 @@ func (h *DefaultHandler) OnResourceLocationUpdated(res *models.ResourceDistribut
 	key := res.ResourceName + ":" + res.Location
 	store.ResourceLocations.Put(key, *res)
 }
+
+// dispatchConfigPush delivers converted config-push data to the handler (CGO-free, for testability).
+func dispatchConfigPush(
+	handler NotificationHandler,
+	queues []models.QueueInfo,
+	resources []models.ResourceDefinitionInfo,
+	hostConfigs []models.HostInfo,
+	cluster *models.ClusterInfo,
+) {
+	for _, q := range queues {
+		handler.OnQueueUpdated(&q)
+	}
+	for _, r := range resources {
+		handler.OnResourceUpdated(&r)
+	}
+	for _, hc := range hostConfigs {
+		handler.OnHostConfigUpdated(&hc)
+	}
+	if cluster != nil {
+		handler.OnClusterUpdated(cluster)
+	}
+}