fix(slack): skip empty progress refreshes

extensions/slack/src/monitor/message-handler/dispatch.preview-fallback.test.ts

@@ -744,6 +744,7 @@ describe("dispatchPreparedSlackMessage preview fallback", () => {
     mockedReplyOptionEvents = [
       { kind: "item", progressText: "tool one" },
       { kind: "item", progressText: "tool two" },
+      { kind: "partial", text: "partial answer" },
     ];
 
     await dispatchPreparedSlackMessage(

extensions/slack/src/monitor/message-handler/dispatch.ts

@@ -984,13 +984,15 @@ export async function dispatchPreparedSlackMessage(prepared: PreparedSlackMessag
       if (statusUpdateCount > 1 && statusUpdateCount % 4 !== 0) {
         return;
       }
-      draftStream?.update(
-        formatChannelProgressDraftText({
-          entry: account.config,
-          lines: previewToolProgressLines,
-          seed: progressSeed,
-        }),
-      );
+      const previewText = formatChannelProgressDraftText({
+        entry: account.config,
+        lines: previewToolProgressLines,
+        seed: progressSeed,
+      });
+      if (!previewText) {
+        return;
+      }
+      draftStream?.update(previewText);
       hasStreamedMessage = true;
       return;
     }