fix(communities): skip bloom filter generation without private key instead of erroring

A missing community private key is the expected state on devices that
don't control the community, not a failure: returning an error made the
caller log noise on every publish. Return nil and skip generation, as in
#7622.

Author: alexjba

protocol/communities/community_bloom_filter.go

@@ -13,11 +13,12 @@ import (
 )
 
 func generateBloomFiltersForChannels(description *protobuf.CommunityDescription, privateKey *ecdsa.PrivateKey) error {
-	// The community private key is absent on devices that don't control the
-	// community (e.g. a freshly profile-synced device); filters can't be
-	// generated without it.
+	// Bloom filters require the community private key to derive the shared secret.
+	// It is absent on devices that don't control the community (e.g. a freshly
+	// profile-synced device), which is expected, so skip generation instead of
+	// dereferencing a nil key.
 	if privateKey == nil {
-		return errors.New("private key is required to generate channel bloom filters")
+		return nil
 	}
 
 	for channelID, channel := range description.Chats {

protocol/communities/community_bloom_filter_test.go

@@ -68,9 +68,9 @@ func (s *CommunityBloomFilterSuite) TestBasic() {
 
 // Regression test: on a device that does not hold the community private key
 // (e.g. right after a profile sync), the publish path can still reach
-// generateBloomFiltersForChannels with a nil key. It must return an error
-// (the caller logs it and marshals the description without filters) instead
-// of crashing the node in ECDH.
+// generateBloomFiltersForChannels with a nil key. Filter generation must be
+// skipped so the description is marshaled without filters, instead of crashing
+// the node in ECDH.
 func (s *CommunityBloomFilterSuite) TestNilPrivateKey() {
 	memberIdentity, err := crypto.GenerateKey()
 	s.Require().NoError(err)
@@ -101,6 +101,6 @@ func (s *CommunityBloomFilterSuite) TestNilPrivateKey() {
 	s.Require().NotPanics(func() {
 		err = generateBloomFiltersForChannels(description, nil)
 	})
-	s.Require().Error(err)
+	s.Require().NoError(err)
 	s.Require().Nil(description.Chats[encryptedChannelID].MembersList)
 }