slack: add config option to disable thread reply broadcasting (#4464)

Adds DisableBroadcastThreadReplies configuration option to control
whether Slack alert status updates in threads are broadcast to the
main channel.

When disabled (set to true), thread replies appear only in the thread.
When enabled (default: false), thread replies broadcast to both the
thread and main channel, preserving current behavior.

Changes:
- Add DisableBroadcastThreadReplies field to Slack config
- Conditionally include slack.MsgOptionBroadcast() based on config
- Auto-generate GraphQL mapping for new config option
- Add smoke test for disabled broadcast behavior

Co-authored-by: Aditya Hebballe <adityahebballe@changejar.in>

Author: AdityaHebballe

config/config.go

@@ -100,6 +100,7 @@ type Config struct {
 
 		SigningSecret       string `password:"true" info:"Signing secret to verify requests from slack."`
 		InteractiveMessages bool   `info:"Enable interactive messages (e.g. buttons)."`
+		DisableBroadcastThreadReplies bool `info:"Disable broadcasting alert status updates in threads to the main channel." public:"true"`
 	}
 
 	Twilio struct {

graphql2/mapconfig.go

@@ -457,11 +457,17 @@ func (s *ChannelSender) SendMessage(ctx context.Context, msg notification.Messag
 			channelID, ts = chanTS(channelID, t.OriginalStatus.ProviderMessageID.ExternalID)
 
 			// Reply in thread if we already sent a message for this alert.
-			opts = append(opts,
+			threadOpts := []slack.MsgOption{
 				slack.MsgOptionTS(ts),
-				slack.MsgOptionBroadcast(),
 				slack.MsgOptionText(alertLink(ctx, t.AlertID, t.Summary), false),
-			)
+			}
+
+			// Conditionally add broadcast based on config (default: enabled)
+			if !cfg.Slack.DisableBroadcastThreadReplies {
+				threadOpts = append(threadOpts, slack.MsgOptionBroadcast())
+			}
+
+			opts = append(opts, threadOpts...)
 			break
 		}
 

notification/slack/channel.go

@@ -42,3 +42,41 @@ func TestSlackNotification(t *testing.T) {
 	// should broadcast reply to channel
 	msg.ExpectBroadcastReply("Alert #1")
 }
+
+// TestSlackNotification_NoBroadcast tests that thread replies don't broadcast when disabled.
+func TestSlackNotification_NoBroadcast(t *testing.T) {
+	t.Parallel()
+
+	sql := `
+	insert into escalation_policies (id, name, repeat)
+	values
+		({{uuid "eid"}}, 'esc policy', 1);
+	insert into escalation_policy_steps (id, escalation_policy_id, delay)
+	values
+		({{uuid "esid"}}, {{uuid "eid"}}, 30);
+
+	insert into notification_channels (id, type, name, value)
+	values
+		({{uuid "chan"}}, 'SLACK', '#test', {{slackChannelID "test"}});
+
+	insert into escalation_policy_actions (escalation_policy_step_id, channel_id)
+	values
+		({{uuid "esid"}}, {{uuid "chan"}});
+
+	insert into services (id, escalation_policy_id, name)
+	values
+		({{uuid "sid"}}, {{uuid "eid"}}, 'service');
+	`
+	h := harness.NewHarness(t, sql, "slack-user-link")
+	defer h.Close()
+
+	// Disable broadcast
+	h.SetConfigValue("Slack.DisableBroadcastThreadReplies", "true")
+
+	h.CreateAlert(h.UUID("sid"), "testing")
+	msg := h.Slack().Channel("test").ExpectMessage("testing")
+
+	h.FastForward(time.Hour)
+	// Should reply in thread WITHOUT broadcast
+	msg.ExpectThreadReply("Alert #1")
+}

test/smoke/slacknotification_test.go

@@ -1657,6 +1657,7 @@ type ConfigID =
   | 'Slack.AccessToken'
   | 'Slack.SigningSecret'
   | 'Slack.InteractiveMessages'
+  | 'Slack.DisableBroadcastThreadReplies'
   | 'Twilio.Enable'
   | 'Twilio.VoiceName'
   | 'Twilio.VoiceLanguage'