diff --git a/src/auto-reply/reply/queue.collect-routing.test.ts b/src/auto-reply/reply/queue.collect-routing.test.ts
index 089f38ae1..118a098cd 100644
--- a/src/auto-reply/reply/queue.collect-routing.test.ts
+++ b/src/auto-reply/reply/queue.collect-routing.test.ts
@@ -29,6 +29,111 @@ function createRun(params: {
   };
 }
 
+describe("followup queue deduplication", () => {
+  it("deduplicates messages with same Discord message_id", async () => {
+    const key = `test-dedup-message-id-${Date.now()}`;
+    const calls: FollowupRun[] = [];
+    const runFollowup = async (run: FollowupRun) => {
+      calls.push(run);
+    };
+    const settings: QueueSettings = {
+      mode: "collect",
+      debounceMs: 0,
+      cap: 50,
+      dropPolicy: "summarize",
+    };
+
+    // First enqueue should succeed
+    const first = enqueueFollowupRun(
+      key,
+      createRun({
+        prompt: "[Discord Guild #test channel id:123] Hello",
+        originatingChannel: "discord",
+        originatingTo: "channel:123",
+      }),
+      settings,
+    );
+    expect(first).toBe(true);
+
+    // Second enqueue with same prompt should be deduplicated
+    const second = enqueueFollowupRun(
+      key,
+      createRun({
+        prompt: "[Discord Guild #test channel id:123] Hello",
+        originatingChannel: "discord",
+        originatingTo: "channel:123",
+      }),
+      settings,
+    );
+    expect(second).toBe(false);
+
+    // Third enqueue with different prompt should succeed
+    const third = enqueueFollowupRun(
+      key,
+      createRun({
+        prompt: "[Discord Guild #test channel id:123] World",
+        originatingChannel: "discord",
+        originatingTo: "channel:123",
+      }),
+      settings,
+    );
+    expect(third).toBe(true);
+
+    scheduleFollowupDrain(key, runFollowup);
+    await expect.poll(() => calls.length).toBe(1);
+    // Should collect both unique messages
+    expect(calls[0]?.prompt).toContain(
+      "[Queued messages while agent was busy]",
+    );
+  });
+
+  it("deduplicates across different providers using exact prompt match", async () => {
+    const key = `test-dedup-whatsapp-${Date.now()}`;
+    const settings: QueueSettings = {
+      mode: "collect",
+      debounceMs: 0,
+      cap: 50,
+      dropPolicy: "summarize",
+    };
+
+    // First enqueue should succeed
+    const first = enqueueFollowupRun(
+      key,
+      createRun({
+        prompt: "Hello world",
+        originatingChannel: "whatsapp",
+        originatingTo: "+1234567890",
+      }),
+      settings,
+    );
+    expect(first).toBe(true);
+
+    // Second enqueue with same prompt should be deduplicated
+    const second = enqueueFollowupRun(
+      key,
+      createRun({
+        prompt: "Hello world",
+        originatingChannel: "whatsapp",
+        originatingTo: "+1234567890",
+      }),
+      settings,
+    );
+    expect(second).toBe(false);
+
+    // Third enqueue with different prompt should succeed
+    const third = enqueueFollowupRun(
+      key,
+      createRun({
+        prompt: "Hello world 2",
+        originatingChannel: "whatsapp",
+        originatingTo: "+1234567890",
+      }),
+      settings,
+    );
+    expect(third).toBe(true);
+  });
+});
+
 describe("followup queue collect routing", () => {
   it("does not collect when destinations differ", async () => {
     const key = `test-collect-diff-to-${Date.now()}`;
diff --git a/src/auto-reply/reply/queue.ts b/src/auto-reply/reply/queue.ts
index 4b14afa43..4bb7ec630 100644
--- a/src/auto-reply/reply/queue.ts
+++ b/src/auto-reply/reply/queue.ts
@@ -337,6 +337,16 @@ function getFollowupQueue(
   FOLLOWUP_QUEUES.set(key, created);
   return created;
 }
+/**
+ * Check if a prompt is already queued using exact match.
+ */
+function isPromptAlreadyQueued(
+  prompt: string,
+  queue: FollowupQueueState,
+): boolean {
+  return queue.items.some((item) => item.prompt === prompt);
+}
+
 export function enqueueFollowupRun(
   key: string,
   run: FollowupRun,
@@ -345,6 +355,12 @@ export function enqueueFollowupRun(
   const queue = getFollowupQueue(key, settings);
   queue.lastEnqueuedAt = Date.now();
   queue.lastRun = run.run;
+
+  // Deduplicate: skip if the same prompt is already queued.
+  if (isPromptAlreadyQueued(run.prompt, queue)) {
+    return false;
+  }
+
   const cap = queue.cap;
   if (cap > 0 && queue.items.length >= cap) {
     if (queue.dropPolicy === "new") {