fix(plugin): close health channel properly in cleanup

Close the health channel in cleanup() before niling to prevent
panics in ListAndWatch() if cleanup happens during channel read.

The WaitGroup ensures the health goroutine has completed before
we close the channel, making this operation safe.

Fixes critical blocker: health channel was never closed, leading
to potential panics and resource leaks.

Refs: NVIDIA#1601
Task: 4/6

Author: ArangoGutierrez

AGENTS.md

@@ -30,15 +30,16 @@
   - Lines: 120-129
   - Changes: Recreate `healthCtx` and `healthCancel` after cancelling for restart support
   - Addresses: Elezar's concern #2 (line 128 - why nil these fields), fixes plugin restart
-  - Commit: (pending)
+  - Commit: cc2a0a77c
 
 ### Phase 3: Health Channel Lifecycle
 
-- [TODO] **Task 4**: Close health channel properly in `cleanup()`
+- [DONE] **Task 4**: Close health channel properly in `cleanup()`
   - File: `internal/plugin/server.go`
   - Lines: 120-129
   - Changes: Close channel before niling to prevent panics
   - Addresses: Devil's advocate blocker - channel never closed
+  - Commit: (pending)
 
 - [TODO] **Task 5**: Handle closed channel in `ListAndWatch()`
   - File: `internal/plugin/server.go`

internal/plugin/server.go

@@ -133,6 +133,12 @@ func (plugin *nvidiaDevicePlugin) cleanup() {
 		plugin.healthCtx, plugin.healthCancel = context.WithCancel(plugin.ctx)
 	}
 	plugin.healthWg.Wait()
+	
+	// Close health channel before niling to prevent panics in ListAndWatch()
+	if plugin.health != nil {
+		close(plugin.health)
+	}
+	
 	plugin.server = nil
 	plugin.health = nil
 	// Do not nil healthCtx or healthCancel - they are needed for restart