fix(telegram): fall back when current preview is missing

src/telegram/bot-message-dispatch.test.ts

@@ -1958,7 +1958,7 @@ describe("dispatchTelegramMessage draft streaming", () => {
     expect(finalTextSentViaDeliverReplies).toBe(true);
   });
 
-  it("keeps preview when Telegram reports the final edit target missing", async () => {
+  it("falls back when Telegram reports the current final edit target missing", async () => {
     const draftStream = createDraftStream(999);
     createTelegramDraftStream.mockReturnValue(draftStream);
     dispatchReplyWithBufferedBlockDispatcher.mockImplementation(
@@ -1980,6 +1980,6 @@ describe("dispatchTelegramMessage draft streaming", () => {
         (r: { text?: string }) => r.text === "Final answer",
       ),
     );
-    expect(finalTextSentViaDeliverReplies).toBe(false);
+    expect(finalTextSentViaDeliverReplies).toBe(true);
   });
 });

src/telegram/lane-delivery-text-deliverer.ts

@@ -25,8 +25,9 @@ function isMessageNotModifiedError(err: unknown): boolean {
 }
 
 /**
- * Returns true when Telegram reports the target message no longer exists.
- * In this case the preview is gone and a fallback send is safe (no duplicate).
+ * Returns true when Telegram rejects an edit because the target message can no
+ * longer be resolved or edited. The caller still needs preview context to
+ * decide whether to retain a different visible preview or fall back to send.
  */
 function isMissingPreviewMessageError(err: unknown): boolean {
   return MESSAGE_NOT_FOUND_RE.test(extractErrorText(err));
@@ -207,6 +208,7 @@ export function createLaneTextDeliverer(params: CreateLaneTextDelivererParams) {
     updateLaneSnapshot: boolean;
     lane: DraftLaneState;
     finalTextAlreadyLanded: boolean;
+    retainAlternatePreviewOnMissingTarget: boolean;
   }): Promise<PreviewEditResult> => {
     try {
       await params.editPreview({
@@ -244,11 +246,17 @@ export function createLaneTextDeliverer(params: CreateLaneTextDelivererParams) {
           return "fallback";
         }
         if (isMissingPreviewMessageError(err)) {
+          if (args.retainAlternatePreviewOnMissingTarget) {
+            params.log(
+              `telegram: ${args.laneName} preview final edit target missing; keeping alternate preview without fallback (${String(err)})`,
+            );
+            params.markDelivered();
+            return "retained";
+          }
           params.log(
-            `telegram: ${args.laneName} preview final edit target missing; keeping existing preview without fallback (${String(err)})`,
+            `telegram: ${args.laneName} preview final edit target missing with no alternate preview; falling back to standard send (${String(err)})`,
           );
-          params.markDelivered();
-          return "retained";
+          return "fallback";
         }
         if (isRecoverableTelegramNetworkError(err, { allowMessageMatch: true })) {
           params.log(
@@ -281,7 +289,11 @@ export function createLaneTextDeliverer(params: CreateLaneTextDelivererParams) {
     previewMessageId: previewMessageIdOverride,
     previewTextSnapshot,
   }: TryUpdatePreviewParams): Promise<PreviewEditResult> => {
-    const editPreview = (messageId: number, finalTextAlreadyLanded: boolean) =>
+    const editPreview = (
+      messageId: number,
+      finalTextAlreadyLanded: boolean,
+      retainAlternatePreviewOnMissingTarget: boolean,
+    ) =>
       tryEditPreviewMessage({
         laneName,
         messageId,
@@ -291,11 +303,13 @@ export function createLaneTextDeliverer(params: CreateLaneTextDelivererParams) {
         updateLaneSnapshot,
         lane,
         finalTextAlreadyLanded,
+        retainAlternatePreviewOnMissingTarget,
       });
     const finalizePreview = (
       previewMessageId: number,
       finalTextAlreadyLanded: boolean,
       hadPreviewMessage: boolean,
+      retainAlternatePreviewOnMissingTarget = false,
     ): PreviewEditResult | Promise<PreviewEditResult> => {
       const currentPreviewText = previewTextSnapshot ?? getLanePreviewText(lane);
       const shouldSkipRegressive = shouldSkipRegressivePreviewUpdate({
@@ -308,7 +322,11 @@ export function createLaneTextDeliverer(params: CreateLaneTextDelivererParams) {
         params.markDelivered();
         return "edited";
       }
-      return editPreview(previewMessageId, finalTextAlreadyLanded);
+      return editPreview(
+        previewMessageId,
+        finalTextAlreadyLanded,
+        retainAlternatePreviewOnMissingTarget,
+      );
     };
     if (!lane.stream) {
       return "fallback";
@@ -346,10 +364,13 @@ export function createLaneTextDeliverer(params: CreateLaneTextDelivererParams) {
     if (typeof previewTargetAfterStop.previewMessageId !== "number") {
       return "fallback";
     }
+    const activePreviewMessageId = lane.stream?.messageId();
     return finalizePreview(
       previewTargetAfterStop.previewMessageId,
       false,
       previewTargetAfterStop.hadPreviewMessage,
+      typeof activePreviewMessageId === "number" &&
+        activePreviewMessageId !== previewTargetAfterStop.previewMessageId,
     );
   };
 

src/telegram/lane-delivery.test.ts

@@ -193,7 +193,7 @@ describe("createLaneTextDeliverer", () => {
     );
   });
 
-  it("keeps preview when Telegram reports the final edit target missing", async () => {
+  it("falls back when Telegram reports the current final edit target missing", async () => {
     const harness = createHarness({ answerMessageId: 999 });
     harness.editPreview.mockRejectedValue(new Error("400: Bad Request: message to edit not found"));
 
@@ -204,11 +204,13 @@ describe("createLaneTextDeliverer", () => {
       infoKind: "final",
     });
 
-    expect(result).toBe("preview-retained");
+    expect(result).toBe("sent");
     expect(harness.editPreview).toHaveBeenCalledTimes(1);
-    expect(harness.sendPayload).not.toHaveBeenCalled();
+    expect(harness.sendPayload).toHaveBeenCalledWith(
+      expect.objectContaining({ text: "Hello final" }),
+    );
     expect(harness.log).toHaveBeenCalledWith(
-      expect.stringContaining("edit target missing; keeping existing preview without fallback"),
+      expect.stringContaining("edit target missing with no alternate preview; falling back"),
     );
   });
 
@@ -445,7 +447,7 @@ describe("createLaneTextDeliverer", () => {
     expect(harness.sendPayload).toHaveBeenCalledTimes(1);
   });
 
-  it("keeps archived preview when its final edit target is missing", async () => {
+  it("falls back when an archived preview edit target is missing and no alternate preview exists", async () => {
     const harness = createHarness();
     harness.archivedAnswerPreviews.push({
       messageId: 5555,
@@ -461,9 +463,36 @@ describe("createLaneTextDeliverer", () => {
       infoKind: "final",
     });
 
+    expect(harness.editPreview).toHaveBeenCalledTimes(1);
+    expect(harness.sendPayload).toHaveBeenCalledWith(
+      expect.objectContaining({ text: "Complete final answer" }),
+    );
+    expect(result).toBe("sent");
+    expect(harness.deletePreviewMessage).toHaveBeenCalledWith(5555);
+  });
+
+  it("keeps the active preview when an archived final edit target is missing", async () => {
+    const harness = createHarness({ answerMessageId: 999 });
+    harness.archivedAnswerPreviews.push({
+      messageId: 5555,
+      textSnapshot: "Partial streaming...",
+      deleteIfUnused: true,
+    });
+    harness.editPreview.mockRejectedValue(new Error("400: Bad Request: message to edit not found"));
+
+    const result = await harness.deliverLaneText({
+      laneName: "answer",
+      text: "Complete final answer",
+      payload: { text: "Complete final answer" },
+      infoKind: "final",
+    });
+
     expect(harness.editPreview).toHaveBeenCalledTimes(1);
     expect(harness.sendPayload).not.toHaveBeenCalled();
     expect(result).toBe("preview-retained");
+    expect(harness.log).toHaveBeenCalledWith(
+      expect.stringContaining("edit target missing; keeping alternate preview without fallback"),
+    );
   });
 
   it("deletes consumed boundary previews after fallback final send", async () => {