fix(gateway): skip text-only assistant media supplements

Gate WebChat assistant-media transcript supplements on resolved display media so stale TTS/media refs cannot persist a text-only gateway-injected duplicate.

Keep resolved media supplements and non-agent command fallback behavior covered by adjacent tests.

Fixes #73956.

CHANGELOG.md

@@ -33,6 +33,7 @@ Docs: https://docs.openclaw.ai
 - Telegram: inherit the process DNS result order for Bot API transport and downgrade recovered sticky IPv4 fallback promotions to debug logs, while keeping pinned-IP escalation warnings visible. Fixes #75904. Thanks @highfly-hi and @neeravmakwana.
 - Web search/MiniMax: allow `MINIMAX_OAUTH_TOKEN` to satisfy MiniMax Search credentials, so OAuth-authorized MiniMax Token Plan setups do not need a separate web-search key. Fixes #65768. Thanks @kikibrian and @zhouhe-xydt.
 - Providers/MiniMax: derive Coding Plan usage polling from the configured MiniMax base URL, so global setups no longer query the CN usage host. Fixes #65054. Thanks @sixone74 and @Yanhu007.
+- Control UI/WebChat: skip assistant-media transcript supplements when stale media refs resolve to no playable media, so text-only final replies are not stored a second time as gateway-injected assistant messages. Fixes #73956. Thanks @HemantSudarshan.
 - Sessions: reject `sessions_send` targets that resolve to thread-scoped chat sessions, so inter-agent coordination cannot be injected into active human-facing Slack or Discord threads. Fixes #52496. Thanks @barry-p5cc.
 - Subagents: honor `sessions_spawn` with `expectsCompletionMessage: false` by skipping parent completion handoff delivery while still running child cleanup. Fixes #75848. Thanks @alfredjbclaw.
 - Media/completions: treat media-only message-tool sends as delivered async completion output, avoiding duplicate raw `MEDIA:` fallback posts after video or music generation finishes.

src/gateway/server-methods/chat.directive-tags.test.ts

@@ -715,6 +715,48 @@ describe("chat directive tag stripping for non-streaming final payloads", () =>
     );
   });
 
+  it("does not persist agent media supplements when no playable media resolves", async () => {
+    const transcriptDir = createTranscriptFixture("openclaw-chat-send-agent-stale-tts-");
+    const staleAudioPath = path.join(transcriptDir, "stale.mp3");
+    mockState.config = {
+      agents: {
+        defaults: {
+          workspace: transcriptDir,
+        },
+      },
+    };
+    mockState.triggerAgentRunStart = true;
+    mockState.dispatchedReplies = [
+      {
+        kind: "final",
+        payload: {
+          text: "Text-only test: one clean reply, no TTS, no media, no tool narration.",
+          mediaUrl: staleAudioPath,
+          mediaUrls: [staleAudioPath],
+          trustedLocalMedia: true,
+        },
+      },
+    ];
+    const respond = vi.fn();
+    const context = createChatContext();
+
+    await runNonStreamingChatSend({
+      context,
+      respond,
+      idempotencyKey: "idem-stale-agent-media",
+      expectBroadcast: false,
+      waitFor: "dedupe",
+    });
+
+    const assistantUpdates = mockState.emittedTranscriptUpdates.filter(
+      (update) =>
+        typeof update.message === "object" &&
+        update.message !== null &&
+        (update.message as { role?: unknown }).role === "assistant",
+    );
+    expect(assistantUpdates).toEqual([]);
+  });
+
   it("keeps visible text on non-agent TTS final media because no model transcript exists", async () => {
     const transcriptDir = createTranscriptFixture("openclaw-chat-send-command-tts-final-");
     const audioPath = path.join(transcriptDir, "tts.mp3");

src/gateway/server-methods/chat.ts

@@ -2265,6 +2265,9 @@ export const chatHandlers: GatewayRequestHandlers = {
         const persistedContentForAppend = hasAssistantDisplayMediaContent(persistedAssistantContent)
           ? persistedAssistantContent
           : undefined;
+        if (!persistedContentForAppend?.length) {
+          return;
+        }
         const transcriptReply =
           mediaMessage?.transcriptText ??
           extractAssistantDisplayTextFromContent(assistantContent) ??