[server] Remove utils.IsClosed[K] helper now unused - #19585

…rtion

- unsubscribe: only close(ch) if ch was actually removed from listeners.
  Calling unsubscribe twice now no-ops the second call instead of
  panicking on close-of-closed-channel.
- unsubscribe: use ok-idiom on v.(*clients) for consistency with Publish.

Both addressed via gemini-code-assist[bot] review on PR meshery#19572.

Signed-off-by: SarthakB11 <[email protected]>

…ble-unsub

Per @chaitanyamedidar review on PR meshery#19572. Three test functions in
server/models/event_broadcast_test.go:

- TestBroadcast_MultipleSubscribersSameID asserts two Subscribe calls
  for the same id both receive the published event. Regresses the
  value-copy clobber that PR meshery#17013 did not fix.
- TestBroadcast_DoubleUnsubscribe asserts calling the returned
  unsubscribe twice is a no-op rather than a panic on close-of-closed
  channel. Regresses the gemini-flagged bug from this PR's first
  revision.
- TestBroadcast_ConcurrentPublishUnsubscribe spins 50 subscribers each
  publishing 10 events plus a background publisher, intended for
  go test -race to catch any reintroduction of the
  send-on-closed-channel race or the listener-slice clobber.

Signed-off-by: SarthakB11 <[email protected]>

- Switch test uuid import from google/uuid to gofrs/uuid (core.Uuid is an
  alias for gofrs/uuid.UUID, which is what the broadcaster Subscribe and
  Publish APIs accept). Fixes the golangci-lint-server typecheck failures
  introduced in 466533c.
- Add doc comment on Publish noting best-effort delivery and the
  buffer-of-one drop semantics.
- Add TestBroadcast_BestEffortDeliveryWhenBufferFull that locks the
  buffer-full drop behavior in place.

Addresses @chaitanyamedidar inline comment on event_broadcast.go:72.

Signed-off-by: SarthakB11 <[email protected]>

…ing sends

The IsClosed[K] helper at server/helpers/utils/utils.go:151 does
'case <-ch: return true' on the passed channel. For a buffered channel
that is open but has a queued value, the receive branch fires and the
value is dropped. The 'Publish*' helpers that use it as a gate then
report the channel closed and skip the send, so events are silently
lost.

Replaced the gate with a non-blocking 'select { case ch <- struct{}{}:
default: }' in:

- server/models/configuration_helper.go: PublishApplications,
  PublishPatterns, PublishFilters
- server/models/dashboard_k8s_resources.go: PublishDashboardK8sResources
- server/models/meshmodel/helper.go: SummaryChannel.Publish
- server/models/k8scontext_helper.go: PublishContext (the inner select
  was already non-blocking; only the redundant IsClosed gate is
  removed)

Same fix pattern as PR meshery#19572 for server/models/event_broadcast.go.
None of these helpers expose an unsubscribe path that closes the
channel, so the send-on-closed-channel risk is bounded to callers that
close their own channels directly, and the non-blocking select handles
the slow-subscriber case identically to the broadcaster.

IsClosed itself is left in place because event_broadcast.go still
references it on master. Removal will be a follow-up once meshery#19572
merges and no callers remain.

Signed-off-by: SarthakB11 <[email protected]>

Per @Amr-Shams and gemini-code-assist review on PR meshery#19580. The
Publish* methods iterated their subscriber slices without holding
mx, while the corresponding Subscribe* methods modified them under
mx.Lock(). A reallocating append concurrent with the publish loop
would race on the slice header and risk reading from a stale backing
array.

Apply the copy-under-lock pattern already used by PublishContext in
server/models/k8scontext_helper.go:

  c.mx.Lock()
  subscribers := make([]chan struct{}, len(c.channel))
  copy(subscribers, c.channel)
  c.mx.Unlock()

  for _, ch := range subscribers {
      select {
      case ch <- struct{}{}:
      default:
      }
  }

Sites updated:

- server/models/configuration_helper.go: PublishApplications,
  PublishPatterns, PublishFilters
- server/models/dashboard_k8s_resources.go: PublishDashboardK8sResources
- server/models/meshmodel/helper.go: SummaryChannel.Publish

PublishContext in k8scontext_helper.go was already correct and is
unchanged.

Signed-off-by: SarthakB11 <[email protected]>

Final step in the IsClosed cleanup sequence after meshery#19572
(event_broadcast.go) and meshery#19580 (configuration_helper.go,
dashboard_k8s_resources.go, meshmodel/helper.go, k8scontext_helper.go)
remove the last callers.

IsClosed was incorrect by construction: on a buffered, still-open
channel with a queued value it did 'case <-ch: return true', draining
the value and falsely reporting closed. With no callers remaining,
keeping it invites the same bug to be reintroduced.

12 LOC deletion. No other changes.

Signed-off-by: SarthakB11 <[email protected]>