fix: prevent duplicate final message when progress already shows the same text

When intermediate text was displayed as a progress message and the final
result had the same content, both the progress message and a separate
final message were sent to Discord. Now detects when the progress message
already shows the final text and finalizes in-place without sending a
duplicate.

src/message-turn-controller.ts

@@ -264,14 +264,16 @@ export class MessageTurnController {
     // Final arrived — flush any buffered progress that isn't the same text,
     // then discard the pending buffer so it never shows up.
     if (text) {
-      if (this.lastIntermediateText && text === this.lastIntermediateText) {
-        // Already sent as intermediate — skip duplicate, just finalize
-        this.lastIntermediateText = null;
+      // If the progress message already shows the same text as the final
+      // result, finalize it in-place instead of sending a duplicate message.
+      const alreadyVisible =
+        this.progressMessageId &&
+        this.latestProgressText === text;
+      if (alreadyVisible) {
         await this.finalizeProgressMessage();
         this.visiblePhase = toVisiblePhase(phase);
         this.latestProgressTextForFinal = null;
       } else {
-        this.lastIntermediateText = null;
         await this.flushPendingProgress(text);
         await this.finalizeProgressMessage();
         await this.deliverFinalText(text);