fix(plugin): handle closed health channel in ListAndWatch

Add ok check when receiving from health channel to gracefully
handle channel closure during cleanup. This prevents potential
panics and ensures clean shutdown when the plugin stops.

Reading from a closed channel returns zero value and ok=false,
which we now check and return gracefully.

Refs: NVIDIA#1601
Task: 5/6

Author: ArangoGutierrez

AGENTS.md

@@ -39,13 +39,14 @@
   - Lines: 120-129
   - Changes: Close channel before niling to prevent panics
   - Addresses: Devil's advocate blocker - channel never closed
-  - Commit: (pending)
+  - Commit: 795807362
 
-- [TODO] **Task 5**: Handle closed channel in `ListAndWatch()`
+- [DONE] **Task 5**: Handle closed channel in `ListAndWatch()`
   - File: `internal/plugin/server.go`
   - Lines: 287-298
   - Changes: Add `ok` check when receiving from health channel
   - Addresses: Graceful handling of channel closure
+  - Commit: (pending)
 
 ### Phase 4: Error Handling Improvements
 

internal/plugin/server.go

@@ -305,7 +305,11 @@ func (plugin *nvidiaDevicePlugin) ListAndWatch(e *pluginapi.Empty, s pluginapi.D
 		select {
 		case <-healthCtx.Done():
 			return nil
-		case d := <-health:
+		case d, ok := <-health:
+			if !ok {
+				// Health channel closed, health checks stopped
+				return nil
+			}
 			// FIXME: there is no way to recover from the Unhealthy state.
 			d.Health = pluginapi.Unhealthy
 			klog.Infof("'%s' device marked unhealthy: %s", plugin.rm.Resource(), d.ID)