fix(telegram): delete orphaned preview message after fallback send

When the answer lane in lane-delivery.ts fails to finalize a preview via
edit and falls back to sendPayload(), the previously-flushed preview
message was left visible. The user sees both the preview and the final
message — the classic 'message appears twice, one disappears' behavior.

The fallback send path now captures the preview message ID before
stopping the draft lane and deletes it after successful delivery.

Closes #38365
Related: #37702, #38434, #33308, #33453

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

@@ -171,6 +171,13 @@ export function createLaneTextDeliverer(params: CreateLaneTextDelivererParams) {
     params.activePreviewLifecycleByLane[laneName] = "complete";
     params.retainPreviewOnCleanupByLane[laneName] = true;
   };
+  const clearActivePreviewState = (laneName: LaneName, lane: DraftLaneState) => {
+    lane.stream?.forceNewMessage?.();
+    lane.lastPartialText = "";
+    lane.hasStreamedMessage = false;
+    params.activePreviewLifecycleByLane[laneName] = "transient";
+    params.retainPreviewOnCleanupByLane[laneName] = false;
+  };
   const isDraftPreviewLane = (lane: DraftLaneState) => lane.stream?.previewMode?.() === "draft";
   const canMaterializeDraftFinal = (
     lane: DraftLaneState,
@@ -529,8 +536,20 @@ export function createLaneTextDeliverer(params: CreateLaneTextDelivererParams) {
           `telegram: preview final too long for edit (${text.length} > ${params.draftMaxChars}); falling back to standard send`,
         );
       }
+      const previewMessageIdBeforeFallback = lane.stream?.messageId();
       await params.stopDraftLane(lane);
+      const previewMessageIdAfterStop = previewMessageIdBeforeFallback ?? lane.stream?.messageId();
       const delivered = await params.sendPayload(params.applyTextToPayload(payload, text));
+      if (delivered && typeof previewMessageIdAfterStop === "number") {
+        try {
+          await params.deletePreviewMessage(previewMessageIdAfterStop);
+          clearActivePreviewState(laneName, lane);
+        } catch (err) {
+          params.log(
+            `telegram: ${laneName} fallback send orphaned preview cleanup failed (${previewMessageIdAfterStop}): ${String(err)}`,
+          );
+        }
+      }
       return delivered ? "sent" : "skipped";
     }
 

src/telegram/lane-delivery.test.ts

@@ -42,8 +42,8 @@ function createHarness(params?: {
   const deletePreviewMessage = vi.fn().mockResolvedValue(undefined);
   const log = vi.fn();
   const markDelivered = vi.fn();
-  const activePreviewLifecycleByLane = { answer: "transient", reasoning: "transient" } as const;
-  const retainPreviewOnCleanupByLane = { answer: false, reasoning: false } as const;
+  const activePreviewLifecycleByLane = { answer: "transient", reasoning: "transient" };
+  const retainPreviewOnCleanupByLane = { answer: false, reasoning: false };
   const archivedAnswerPreviews: Array<{
     messageId: number;
     textSnapshot: string;
@@ -53,8 +53,8 @@ function createHarness(params?: {
   const deliverLaneText = createLaneTextDeliverer({
     lanes,
     archivedAnswerPreviews,
-    activePreviewLifecycleByLane: { ...activePreviewLifecycleByLane },
-    retainPreviewOnCleanupByLane: { ...retainPreviewOnCleanupByLane },
+    activePreviewLifecycleByLane,
+    retainPreviewOnCleanupByLane,
     draftMaxChars: params?.draftMaxChars ?? 4_096,
     applyTextToPayload: (payload: ReplyPayload, text: string) => ({ ...payload, text }),
     sendPayload,
@@ -81,6 +81,8 @@ function createHarness(params?: {
     log,
     markDelivered,
     archivedAnswerPreviews,
+    activePreviewLifecycleByLane,
+    retainPreviewOnCleanupByLane,
   };
 }
 
@@ -473,6 +475,29 @@ describe("createLaneTextDeliverer", () => {
     expect(harness.deletePreviewMessage).toHaveBeenCalledWith(5555);
   });
 
+  it("clears active preview state after successful fallback orphan cleanup", async () => {
+    const harness = createHarness({
+      answerMessageId: 5555,
+      answerHasStreamedMessage: true,
+      answerLastPartialText: "Partial streaming...",
+    });
+
+    const result = await harness.deliverLaneText({
+      laneName: "answer",
+      text: "Final with media",
+      payload: { text: "Final with media", mediaUrl: "file:///tmp/example.png" },
+      infoKind: "final",
+    });
+
+    expect(result).toBe("sent");
+    expect(harness.deletePreviewMessage).toHaveBeenCalledWith(5555);
+    expect(harness.answer.stream?.forceNewMessage).toHaveBeenCalledTimes(1);
+    expect(harness.lanes.answer.hasStreamedMessage).toBe(false);
+    expect(harness.lanes.answer.lastPartialText).toBe("");
+    expect(harness.activePreviewLifecycleByLane.answer).toBe("transient");
+    expect(harness.retainPreviewOnCleanupByLane.answer).toBe(false);
+  });
+
   it("keeps the active preview when an archived final edit target is missing", async () => {
     const harness = createHarness({ answerMessageId: 999 });
     harness.archivedAnswerPreviews.push({