CBG-4928 do not log warning for closed blip sender

[torcolvin]

CBG-4928 do not log warning for closed blip sender

This should prevent a log message as below when a blip connection is closed and it can not longer send changes. I believe a blip connection could be closed due to normal network disconnections:

[WRN] c:[231d979a] db:db col:col2 Error from bh.handleChangesResponse: use of closed BLIP sender -- db.(*blipHandler).sendBatchOfChanges.func1() at blip_handler.go:614

It is OK to not enter fatalErrorCallback

sync_gateway/db/active_replicator_push.go

Lines 211 to 213 in b8b689b

	apr.blipSyncContext.fatalErrorCallback = func(err error) {
	if strings.Contains(err.Error(), ErrUseProposeChanges.Message) {

since if the sender is closed it will enter https://github.com/couchbase/sync_gateway/blob/main/db/active_replicator.go#L238 which will close and reconnect.

This was hard to unit test, but is observed in real world logs, so pushing this change to avoid unexpected logs. In order to test this, I believe you have to have the sender closed at the right time.

NOTE: this is only one part of CBG-4928 and there is a second part needed to address:

[WRN] c:[393a64c4] db:db col:col1 Error retrieving changes for channel "<ud>b2</ud>": Changes feed cancelled while waiting for view lock -- db.(*DatabaseCollectionWithUser).changesFeed.func1() at changes.go:437
[WRN] c:[393a64c4] db:db col:col1 MultiChangesFeed got error reading changes feed: Error while building channel feed -- db.(*DatabaseCollectionWithUser).SimpleMultiChangesFeed.func1() at changes.go:914

[Copilot]

Pull Request Overview

This PR addresses a false alarm in logging when BLIP connections close normally during replication by filtering out expected errors from closed BLIP senders.

• Prevents warning logs when BLIP sender closes during normal network disconnections
• Adds error filtering to avoid invoking fatal error callbacks for expected closed sender errors

[Copilot]

[nitpick] The condition is now complex with multiple checks on a single line. Consider extracting the error check to a separate variable for improved readability: if err := bh.handleChangesResponse(...); err != nil { if !errors.Is(err, ErrClosedBLIPSender) { ... } }