diff --git a/CHANGELOG.md b/CHANGELOG.md
index d87f7c099..0631d4d4e 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -57,6 +57,7 @@
 - Auto-reply: relax reply tag parsing to allow whitespace. (#560) — thanks @mcinteerj
 - Auto-reply: add per-provider block streaming toggles and coalesce streamed blocks to reduce line spam. (#536) — thanks @mcinteerj
 - Auto-reply: fix /status usage summary filtering for the active provider.
+- Auto-reply: deduplicate followup queue entries using message id/routing to avoid duplicate replies. (#600) — thanks @samratjha96
 - Status: show provider prefix in /status model display. (#506) — thanks @mcinteerj
 - Status: compact /status with session token usage + estimated cost, add `/cost` per-response usage lines (tokens-only for OAuth).
 - Status: show active auth profile and key snippet in /status.
diff --git a/src/auto-reply/reply.ts b/src/auto-reply/reply.ts
index a8e7de8fa..c8d0d664d 100644
--- a/src/auto-reply/reply.ts
+++ b/src/auto-reply/reply.ts
@@ -846,6 +846,7 @@ export async function getReplyFromConfig(
   const authProfileId = sessionEntry?.authProfileOverride;
   const followupRun = {
     prompt: queuedBody,
+    messageId: sessionCtx.MessageSid,
     summaryLine: baseBodyTrimmedRaw,
     enqueuedAt: Date.now(),
     // Originating channel for reply routing.
diff --git a/src/auto-reply/reply/queue.collect-routing.test.ts b/src/auto-reply/reply/queue.collect-routing.test.ts
index 089f38ae1..74295f1ae 100644
--- a/src/auto-reply/reply/queue.collect-routing.test.ts
+++ b/src/auto-reply/reply/queue.collect-routing.test.ts
@@ -6,14 +6,20 @@ import { enqueueFollowupRun, scheduleFollowupDrain } from "./queue.js";
 
 function createRun(params: {
   prompt: string;
+  messageId?: string;
   originatingChannel?: FollowupRun["originatingChannel"];
   originatingTo?: string;
+  originatingAccountId?: string;
+  originatingThreadId?: number;
 }): FollowupRun {
   return {
     prompt: params.prompt,
+    messageId: params.messageId,
     enqueuedAt: Date.now(),
     originatingChannel: params.originatingChannel,
     originatingTo: params.originatingTo,
+    originatingAccountId: params.originatingAccountId,
+    originatingThreadId: params.originatingThreadId,
     run: {
       agentId: "agent",
       agentDir: "/tmp",
@@ -29,6 +35,146 @@ function createRun(params: {
   };
 }
 
+describe("followup queue deduplication", () => {
+  it("deduplicates messages with same Discord message_id", async () => {
+    const key = `test-dedup-message-id-${Date.now()}`;
+    const calls: FollowupRun[] = [];
+    const runFollowup = async (run: FollowupRun) => {
+      calls.push(run);
+    };
+    const settings: QueueSettings = {
+      mode: "collect",
+      debounceMs: 0,
+      cap: 50,
+      dropPolicy: "summarize",
+    };
+
+    // First enqueue should succeed
+    const first = enqueueFollowupRun(
+      key,
+      createRun({
+        prompt: "[Discord Guild #test channel id:123] Hello",
+        messageId: "m1",
+        originatingChannel: "discord",
+        originatingTo: "channel:123",
+      }),
+      settings,
+    );
+    expect(first).toBe(true);
+
+    // Second enqueue with same message id should be deduplicated
+    const second = enqueueFollowupRun(
+      key,
+      createRun({
+        prompt: "[Discord Guild #test channel id:123] Hello (dupe)",
+        messageId: "m1",
+        originatingChannel: "discord",
+        originatingTo: "channel:123",
+      }),
+      settings,
+    );
+    expect(second).toBe(false);
+
+    // Third enqueue with different message id should succeed
+    const third = enqueueFollowupRun(
+      key,
+      createRun({
+        prompt: "[Discord Guild #test channel id:123] World",
+        messageId: "m2",
+        originatingChannel: "discord",
+        originatingTo: "channel:123",
+      }),
+      settings,
+    );
+    expect(third).toBe(true);
+
+    scheduleFollowupDrain(key, runFollowup);
+    await expect.poll(() => calls.length).toBe(1);
+    // Should collect both unique messages
+    expect(calls[0]?.prompt).toContain(
+      "[Queued messages while agent was busy]",
+    );
+  });
+
+  it("deduplicates exact prompt when routing matches and no message id", async () => {
+    const key = `test-dedup-whatsapp-${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);
+  });
+
+  it("does not deduplicate across different providers without message id", async () => {
+    const key = `test-dedup-cross-provider-${Date.now()}`;
+    const settings: QueueSettings = {
+      mode: "collect",
+      debounceMs: 0,
+      cap: 50,
+      dropPolicy: "summarize",
+    };
+
+    const first = enqueueFollowupRun(
+      key,
+      createRun({
+        prompt: "Same text",
+        originatingChannel: "whatsapp",
+        originatingTo: "+1234567890",
+      }),
+      settings,
+    );
+    expect(first).toBe(true);
+
+    const second = enqueueFollowupRun(
+      key,
+      createRun({
+        prompt: "Same text",
+        originatingChannel: "discord",
+        originatingTo: "channel:123",
+      }),
+      settings,
+    );
+    expect(second).toBe(true);
+  });
+});
+
 describe("followup queue collect routing", () => {
   it("does not collect when destinations differ", async () => {
     const key = `test-collect-diff-to-${Date.now()}`;
diff --git a/src/auto-reply/reply/queue.ts b/src/auto-reply/reply/queue.ts
index 4b14afa43..7fabf083b 100644
--- a/src/auto-reply/reply/queue.ts
+++ b/src/auto-reply/reply/queue.ts
@@ -27,6 +27,8 @@ export type QueueSettings = {
 };
 export type FollowupRun = {
   prompt: string;
+  /** Provider message ID, when available (for deduplication). */
+  messageId?: string;
   summaryLine?: string;
   enqueuedAt: number;
   /**
@@ -337,14 +339,45 @@ function getFollowupQueue(
   FOLLOWUP_QUEUES.set(key, created);
   return created;
 }
+/**
+ * Check if a run is already queued using a stable dedup key.
+ */
+function isRunAlreadyQueued(
+  run: FollowupRun,
+  queue: FollowupQueueState,
+): boolean {
+  const hasSameRouting = (item: FollowupRun) =>
+    item.originatingChannel === run.originatingChannel &&
+    item.originatingTo === run.originatingTo &&
+    item.originatingAccountId === run.originatingAccountId &&
+    item.originatingThreadId === run.originatingThreadId;
+
+  const messageId = run.messageId?.trim();
+  if (messageId) {
+    return queue.items.some(
+      (item) => item.messageId?.trim() === messageId && hasSameRouting(item),
+    );
+  }
+  return queue.items.some(
+    (item) => item.prompt === run.prompt && hasSameRouting(item),
+  );
+}
+
 export function enqueueFollowupRun(
   key: string,
   run: FollowupRun,
   settings: QueueSettings,
 ): boolean {
   const queue = getFollowupQueue(key, settings);
+
+  // Deduplicate: skip if the same message is already queued.
+  if (isRunAlreadyQueued(run, queue)) {
+    return false;
+  }
+
   queue.lastEnqueuedAt = Date.now();
   queue.lastRun = run.run;
+
   const cap = queue.cap;
   if (cap > 0 && queue.items.length >= cap) {
     if (queue.dropPolicy === "new") {