fix(FN-7965): surface duplicate decisions

Show a clear operator-decision badge and deliver an idempotent mailbox prompt for triage duplicate markers.

Fusion-Task-Id: FN-7965

packages/engine/src/__tests__/notification-service.test.ts

@@ -262,6 +262,42 @@ describe("NotificationService", () => {
     expect(input.content).toContain("https://dash.example/?project=p1&task=FN-1");
   });
 
+  it("writes one mailbox message when a triage duplicate needs an operator decision", async () => {
+    const store = createStore({ ntfyEnabled: false });
+    const idempotencyKeys = new Set<string>();
+    let insertedCount = 0;
+    const sendMessageOnce = vi.fn(async (input: any, key: string) => {
+      const inserted = !idempotencyKeys.has(key);
+      idempotencyKeys.add(key);
+      if (inserted) insertedCount += 1;
+      return { message: { ...input, id: "msg-once-duplicate", read: false, createdAt: "", updatedAt: "" }, inserted };
+    });
+    const messageStore = Object.assign(new EventEmitter(), { sendMessageOnce });
+    const service = new NotificationService(store as any, { projectId: "p1", messageStore: messageStore as any });
+    await service.start();
+
+    const duplicate = task({
+      paused: true,
+      pausedReason: "duplicate-decision-required",
+      sourceMetadata: { duplicateSource: "triage-marker", nearDuplicateOf: "FN-7961" },
+    });
+    store.emit("task:updated", duplicate);
+    store.emit("task:updated", duplicate);
+    await vi.waitFor(() => expect(sendMessageOnce).toHaveBeenCalledTimes(2));
+    expect(insertedCount).toBe(1);
+
+    for (const [input, key] of sendMessageOnce.mock.calls) {
+      expect(key).toBe("triage-duplicate-decision:FN-1");
+      expect(input).toMatchObject({
+        type: "system",
+        toId: "dashboard",
+        toType: "user",
+        metadata: { taskId: "FN-1", canonicalTaskId: "FN-7961", kind: "triage-duplicate-decision" },
+      });
+      expect(input.content).toContain("flagged as a duplicate of FN-7961");
+    }
+  });
+
   it("labels the replan-cap escalation reason in the approval mailbox message", async () => {
     const store = createStore({ ntfyEnabled: true, ntfyTopic: "topic" });
     const sendMessageOnce = vi.fn(async (input: any, _key: string) => ({

packages/engine/src/notification/notification-service.ts

@@ -262,6 +262,10 @@ export class NotificationService {
       void this.writeAwaitingApprovalMailboxMessage(task);
     }
 
+    if (this.isTriageDuplicateDecision(task)) {
+      void this.writeTriageDuplicateDecisionMailboxMessage(task);
+    }
+
     if (!this.notificationsEnabled) {
       return;
     }
@@ -386,6 +390,51 @@ export class NotificationService {
     }
   }
 
+  private isTriageDuplicateDecision(task: Task): boolean {
+    return task.paused === true
+      && task.pausedReason === "duplicate-decision-required"
+      && task.sourceMetadata?.duplicateSource === "triage-marker"
+      && typeof task.sourceMetadata.nearDuplicateOf === "string";
+  }
+
+  /** Write one durable operator prompt for a duplicate candidate, independent of push configuration. */
+  private async writeTriageDuplicateDecisionMailboxMessage(task: Task): Promise<void> {
+    try {
+      const messageStore = this.options.messageStore;
+      if (!messageStore?.sendMessageOnce) {
+        return;
+      }
+      const canonicalTaskId = task.sourceMetadata?.nearDuplicateOf;
+      if (typeof canonicalTaskId !== "string") {
+        return;
+      }
+      const link = buildNtfyClickUrl({
+        dashboardHost: this.dashboardHost,
+        projectId: this.options.projectId,
+        taskId: task.id,
+      });
+      const content = [
+        `**${formatTaskIdentifier(task)} needs your decision**`,
+        "",
+        `It was flagged as a duplicate of ${canonicalTaskId}. Keep it to continue planning, or delete it if the work is already covered.`,
+        ...(link ? ["", `[Open ${task.id}](${link})`] : []),
+      ].join("\n");
+      await messageStore.sendMessageOnce({
+        fromId: "system",
+        fromType: "system",
+        toId: DASHBOARD_USER_ID,
+        toType: "user",
+        type: "system",
+        content,
+        metadata: { taskId: task.id, canonicalTaskId, kind: "triage-duplicate-decision" },
+      }, `triage-duplicate-decision:${task.id}`);
+    } catch (error) {
+      schedulerLog.log(
+        `[notify] ${task.id} triage duplicate-decision mailbox message failed: ${error instanceof Error ? error.message : String(error)}`,
+      );
+    }
+  }
+
   private handleTaskMerged = (result: MergeResult): void => {
     void this.handleTaskMergedAsync(result);
   };