diff --git a/src/auto-reply/reply/dispatch-from-config.ts b/src/auto-reply/reply/dispatch-from-config.ts
index 0e6654cfa..26961ad7c 100644
--- a/src/auto-reply/reply/dispatch-from-config.ts
+++ b/src/auto-reply/reply/dispatch-from-config.ts
@@ -25,6 +25,8 @@ export async function dispatchReplyFromConfig(params: {
   // This handles cross-provider routing (e.g., message from Telegram being processed
   // by a shared session that's currently on Slack) while preserving normal dispatcher
   // flow when the provider handles its own messages.
+  //
+  // Debug: `pnpm test src/auto-reply/reply/dispatch-from-config.test.ts`
   const originatingChannel = ctx.OriginatingChannel;
   const originatingTo = ctx.OriginatingTo;
   const currentSurface = (ctx.Surface ?? ctx.Provider)?.toLowerCase();
diff --git a/src/auto-reply/reply/queue.ts b/src/auto-reply/reply/queue.ts
index a5208e674..e2b089144 100644
--- a/src/auto-reply/reply/queue.ts
+++ b/src/auto-reply/reply/queue.ts
@@ -442,6 +442,10 @@ export function scheduleFollowupDrain(
       while (queue.items.length > 0 || queue.droppedCount > 0) {
         await waitForQueueDebounce(queue);
         if (queue.mode === "collect") {
+          // Once the batch is mixed, never collect again within this drain.
+          // Prevents “collect after shift” collapsing different targets.
+          //
+          // Debug: `pnpm test src/auto-reply/reply/queue.collect-routing.test.ts`
           if (forceIndividualCollect) {
             const next = queue.items.shift();
             if (!next) break;
diff --git a/src/auto-reply/reply/route-reply.test.ts b/src/auto-reply/reply/route-reply.test.ts
new file mode 100644
index 000000000..27f2bcdef
--- /dev/null
+++ b/src/auto-reply/reply/route-reply.test.ts
@@ -0,0 +1,115 @@
+import { describe, expect, it, vi } from "vitest";
+
+const mocks = vi.hoisted(() => ({
+  sendMessageDiscord: vi.fn(async () => ({ messageId: "m1", channelId: "c1" })),
+  sendMessageIMessage: vi.fn(async () => ({ messageId: "ok" })),
+  sendMessageSignal: vi.fn(async () => ({ messageId: "t1" })),
+  sendMessageSlack: vi.fn(async () => ({ messageId: "m1", channelId: "c1" })),
+  sendMessageTelegram: vi.fn(async () => ({ messageId: "m1", chatId: "c1" })),
+  sendMessageWhatsApp: vi.fn(async () => ({ messageId: "m1", toJid: "jid" })),
+}));
+
+vi.mock("../../discord/send.js", () => ({
+  sendMessageDiscord: mocks.sendMessageDiscord,
+}));
+vi.mock("../../imessage/send.js", () => ({
+  sendMessageIMessage: mocks.sendMessageIMessage,
+}));
+vi.mock("../../signal/send.js", () => ({
+  sendMessageSignal: mocks.sendMessageSignal,
+}));
+vi.mock("../../slack/send.js", () => ({
+  sendMessageSlack: mocks.sendMessageSlack,
+}));
+vi.mock("../../telegram/send.js", () => ({
+  sendMessageTelegram: mocks.sendMessageTelegram,
+}));
+vi.mock("../../web/outbound.js", () => ({
+  sendMessageWhatsApp: mocks.sendMessageWhatsApp,
+}));
+
+const { routeReply } = await import("./route-reply.js");
+
+describe("routeReply", () => {
+  it("no-ops on empty payload", async () => {
+    mocks.sendMessageSlack.mockClear();
+    const res = await routeReply({
+      payload: {},
+      channel: "slack",
+      to: "channel:C123",
+      cfg: {} as never,
+    });
+    expect(res.ok).toBe(true);
+    expect(mocks.sendMessageSlack).not.toHaveBeenCalled();
+  });
+
+  it("passes thread id to Telegram sends", async () => {
+    mocks.sendMessageTelegram.mockClear();
+    await routeReply({
+      payload: { text: "hi" },
+      channel: "telegram",
+      to: "telegram:123",
+      threadId: 42,
+      cfg: {} as never,
+    });
+    expect(mocks.sendMessageTelegram).toHaveBeenCalledWith(
+      "telegram:123",
+      "hi",
+      expect.objectContaining({ messageThreadId: 42 }),
+    );
+  });
+
+  it("uses replyToId as threadTs for Slack", async () => {
+    mocks.sendMessageSlack.mockClear();
+    await routeReply({
+      payload: { text: "hi", replyToId: "1710000000.0001" },
+      channel: "slack",
+      to: "channel:C123",
+      cfg: {} as never,
+    });
+    expect(mocks.sendMessageSlack).toHaveBeenCalledWith(
+      "channel:C123",
+      "hi",
+      expect.objectContaining({ threadTs: "1710000000.0001" }),
+    );
+  });
+
+  it("sends multiple mediaUrls (caption only on first)", async () => {
+    mocks.sendMessageSlack.mockClear();
+    await routeReply({
+      payload: { text: "caption", mediaUrls: ["a", "b"] },
+      channel: "slack",
+      to: "channel:C123",
+      cfg: {} as never,
+    });
+    expect(mocks.sendMessageSlack).toHaveBeenCalledTimes(2);
+    expect(mocks.sendMessageSlack).toHaveBeenNthCalledWith(
+      1,
+      "channel:C123",
+      "caption",
+      expect.objectContaining({ mediaUrl: "a" }),
+    );
+    expect(mocks.sendMessageSlack).toHaveBeenNthCalledWith(
+      2,
+      "channel:C123",
+      "",
+      expect.objectContaining({ mediaUrl: "b" }),
+    );
+  });
+
+  it("routes WhatsApp via outbound sender (accountId honored)", async () => {
+    mocks.sendMessageWhatsApp.mockClear();
+    await routeReply({
+      payload: { text: "hi" },
+      channel: "whatsapp",
+      to: "+15551234567",
+      accountId: "acc-1",
+      cfg: {} as never,
+    });
+    expect(mocks.sendMessageWhatsApp).toHaveBeenCalledWith(
+      "+15551234567",
+      "hi",
+      expect.objectContaining({ accountId: "acc-1", verbose: false }),
+    );
+  });
+});
diff --git a/src/auto-reply/reply/route-reply.ts b/src/auto-reply/reply/route-reply.ts
index 39bb28ab8..cd8b0efdc 100644
--- a/src/auto-reply/reply/route-reply.ts
+++ b/src/auto-reply/reply/route-reply.ts
@@ -54,6 +54,7 @@ export async function routeReply(
 ): Promise<RouteReplyResult> {
   const { payload, channel, to, accountId, threadId } = params;
 
+  // Debug: `pnpm test src/auto-reply/reply/route-reply.test.ts`
   const text = payload.text ?? "";
   const mediaUrls = (payload.mediaUrls?.filter(Boolean) ?? []).length
     ? (payload.mediaUrls?.filter(Boolean) as string[])