diff --git a/extensions/zalo/src/channel.sendpayload.test.ts b/extensions/zalo/src/channel.sendpayload.test.ts
index 6cc072ac6dd..27acb737f9f 100644
--- a/extensions/zalo/src/channel.sendpayload.test.ts
+++ b/extensions/zalo/src/channel.sendpayload.test.ts
@@ -1,5 +1,9 @@
 import type { ReplyPayload } from "openclaw/plugin-sdk/zalo";
 import { beforeEach, describe, expect, it, vi } from "vitest";
+import {
+  installSendPayloadContractSuite,
+  primeSendMock,
+} from "../../../src/test-utils/send-payload-contract.js";
 import { zaloPlugin } from "./channel.js";
 
 vi.mock("./send.js", () => ({
@@ -25,78 +29,16 @@ describe("zaloPlugin outbound sendPayload", () => {
     mockedSend.mockResolvedValue({ ok: true, messageId: "zl-1" });
   });
 
-  it("text-only delegates to sendText", async () => {
-    mockedSend.mockResolvedValue({ ok: true, messageId: "zl-t1" });
-
-    const result = await zaloPlugin.outbound!.sendPayload!(baseCtx({ text: "hello" }));
-
-    expect(mockedSend).toHaveBeenCalledWith("123456789", "hello", expect.any(Object));
-    expect(result).toMatchObject({ channel: "zalo", messageId: "zl-t1" });
-  });
-
-  it("single media delegates to sendMedia", async () => {
-    mockedSend.mockResolvedValue({ ok: true, messageId: "zl-m1" });
-
-    const result = await zaloPlugin.outbound!.sendPayload!(
-      baseCtx({ text: "cap", mediaUrl: "https://example.com/a.jpg" }),
-    );
-
-    expect(mockedSend).toHaveBeenCalledWith(
-      "123456789",
-      "cap",
-      expect.objectContaining({ mediaUrl: "https://example.com/a.jpg" }),
-    );
-    expect(result).toMatchObject({ channel: "zalo" });
-  });
-
-  it("multi-media iterates URLs with caption on first", async () => {
-    mockedSend
-      .mockResolvedValueOnce({ ok: true, messageId: "zl-1" })
-      .mockResolvedValueOnce({ ok: true, messageId: "zl-2" });
-
-    const result = await zaloPlugin.outbound!.sendPayload!(
-      baseCtx({
-        text: "caption",
-        mediaUrls: ["https://example.com/1.jpg", "https://example.com/2.jpg"],
-      }),
-    );
-
-    expect(mockedSend).toHaveBeenCalledTimes(2);
-    expect(mockedSend).toHaveBeenNthCalledWith(
-      1,
-      "123456789",
-      "caption",
-      expect.objectContaining({ mediaUrl: "https://example.com/1.jpg" }),
-    );
-    expect(mockedSend).toHaveBeenNthCalledWith(
-      2,
-      "123456789",
-      "",
-      expect.objectContaining({ mediaUrl: "https://example.com/2.jpg" }),
-    );
-    expect(result).toMatchObject({ channel: "zalo", messageId: "zl-2" });
-  });
-
-  it("empty payload returns no-op", async () => {
-    const result = await zaloPlugin.outbound!.sendPayload!(baseCtx({}));
-
-    expect(mockedSend).not.toHaveBeenCalled();
-    expect(result).toEqual({ channel: "zalo", messageId: "" });
-  });
-
-  it("chunking splits long text", async () => {
-    mockedSend
-      .mockResolvedValueOnce({ ok: true, messageId: "zl-c1" })
-      .mockResolvedValueOnce({ ok: true, messageId: "zl-c2" });
-
-    const longText = "a".repeat(3000);
-    const result = await zaloPlugin.outbound!.sendPayload!(baseCtx({ text: longText }));
-
-    // textChunkLimit is 2000 with chunkTextForOutbound, so it should split
-    expect(mockedSend.mock.calls.length).toBeGreaterThanOrEqual(2);
-    for (const call of mockedSend.mock.calls) {
-      expect((call[1] as string).length).toBeLessThanOrEqual(2000);
-    }
-    expect(result).toMatchObject({ channel: "zalo" });
+  installSendPayloadContractSuite({
+    channel: "zalo",
+    chunking: { mode: "split", longTextLength: 3000, maxChunkLength: 2000 },
+    createHarness: ({ payload, sendResults }) => {
+      primeSendMock(mockedSend, { ok: true, messageId: "zl-1" }, sendResults);
+      return {
+        run: async () => await zaloPlugin.outbound!.sendPayload!(baseCtx(payload)),
+        sendMock: mockedSend,
+        to: "123456789",
+      };
+    },
   });
 });
diff --git a/extensions/zalouser/src/channel.sendpayload.test.ts b/extensions/zalouser/src/channel.sendpayload.test.ts
index 534f9c39b95..0cef65f8c05 100644
--- a/extensions/zalouser/src/channel.sendpayload.test.ts
+++ b/extensions/zalouser/src/channel.sendpayload.test.ts
@@ -1,5 +1,9 @@
 import type { ReplyPayload } from "openclaw/plugin-sdk/zalouser";
 import { beforeEach, describe, expect, it, vi } from "vitest";
+import {
+  installSendPayloadContractSuite,
+  primeSendMock,
+} from "../../../src/test-utils/send-payload-contract.js";
 import { zalouserPlugin } from "./channel.js";
 
 vi.mock("./send.js", () => ({
@@ -40,15 +44,6 @@ describe("zalouserPlugin outbound sendPayload", () => {
     mockedSend.mockResolvedValue({ ok: true, messageId: "zlu-1" });
   });
 
-  it("text-only delegates to sendText", async () => {
-    mockedSend.mockResolvedValue({ ok: true, messageId: "zlu-t1" });
-
-    const result = await zalouserPlugin.outbound!.sendPayload!(baseCtx({ text: "hello" }));
-
-    expect(mockedSend).toHaveBeenCalledWith("987654321", "hello", expect.any(Object));
-    expect(result).toMatchObject({ channel: "zalouser", messageId: "zlu-t1" });
-  });
-
   it("group target delegates with isGroup=true and stripped threadId", async () => {
     mockedSend.mockResolvedValue({ ok: true, messageId: "zlu-g1" });
 
@@ -65,21 +60,6 @@ describe("zalouserPlugin outbound sendPayload", () => {
     expect(result).toMatchObject({ channel: "zalouser", messageId: "zlu-g1" });
   });
 
-  it("single media delegates to sendMedia", async () => {
-    mockedSend.mockResolvedValue({ ok: true, messageId: "zlu-m1" });
-
-    const result = await zalouserPlugin.outbound!.sendPayload!(
-      baseCtx({ text: "cap", mediaUrl: "https://example.com/a.jpg" }),
-    );
-
-    expect(mockedSend).toHaveBeenCalledWith(
-      "987654321",
-      "cap",
-      expect.objectContaining({ mediaUrl: "https://example.com/a.jpg" }),
-    );
-    expect(result).toMatchObject({ channel: "zalouser" });
-  });
-
   it("treats bare numeric targets as direct chats for backward compatibility", async () => {
     mockedSend.mockResolvedValue({ ok: true, messageId: "zlu-d1" });
 
@@ -112,55 +92,17 @@ describe("zalouserPlugin outbound sendPayload", () => {
     expect(result).toMatchObject({ channel: "zalouser", messageId: "zlu-g-native" });
   });
 
-  it("multi-media iterates URLs with caption on first", async () => {
-    mockedSend
-      .mockResolvedValueOnce({ ok: true, messageId: "zlu-1" })
-      .mockResolvedValueOnce({ ok: true, messageId: "zlu-2" });
-
-    const result = await zalouserPlugin.outbound!.sendPayload!(
-      baseCtx({
-        text: "caption",
-        mediaUrls: ["https://example.com/1.jpg", "https://example.com/2.jpg"],
-      }),
-    );
-
-    expect(mockedSend).toHaveBeenCalledTimes(2);
-    expect(mockedSend).toHaveBeenNthCalledWith(
-      1,
-      "987654321",
-      "caption",
-      expect.objectContaining({ mediaUrl: "https://example.com/1.jpg" }),
-    );
-    expect(mockedSend).toHaveBeenNthCalledWith(
-      2,
-      "987654321",
-      "",
-      expect.objectContaining({ mediaUrl: "https://example.com/2.jpg" }),
-    );
-    expect(result).toMatchObject({ channel: "zalouser", messageId: "zlu-2" });
-  });
-
-  it("empty payload returns no-op", async () => {
-    const result = await zalouserPlugin.outbound!.sendPayload!(baseCtx({}));
-
-    expect(mockedSend).not.toHaveBeenCalled();
-    expect(result).toEqual({ channel: "zalouser", messageId: "" });
-  });
-
-  it("chunking splits long text", async () => {
-    mockedSend
-      .mockResolvedValueOnce({ ok: true, messageId: "zlu-c1" })
-      .mockResolvedValueOnce({ ok: true, messageId: "zlu-c2" });
-
-    const longText = "a".repeat(3000);
-    const result = await zalouserPlugin.outbound!.sendPayload!(baseCtx({ text: longText }));
-
-    // textChunkLimit is 2000 with chunkTextForOutbound, so it should split
-    expect(mockedSend.mock.calls.length).toBeGreaterThanOrEqual(2);
-    for (const call of mockedSend.mock.calls) {
-      expect((call[1] as string).length).toBeLessThanOrEqual(2000);
-    }
-    expect(result).toMatchObject({ channel: "zalouser" });
+  installSendPayloadContractSuite({
+    channel: "zalouser",
+    chunking: { mode: "split", longTextLength: 3000, maxChunkLength: 2000 },
+    createHarness: ({ payload, sendResults }) => {
+      primeSendMock(mockedSend, { ok: true, messageId: "zlu-1" }, sendResults);
+      return {
+        run: async () => await zalouserPlugin.outbound!.sendPayload!(baseCtx(payload)),
+        sendMock: mockedSend,
+        to: "987654321",
+      };
+    },
   });
 });
 
diff --git a/src/channels/plugins/outbound/direct-text-media.sendpayload.test.ts b/src/channels/plugins/outbound/direct-text-media.sendpayload.test.ts
index 0e5c2ba01db..42971f1e89c 100644
--- a/src/channels/plugins/outbound/direct-text-media.sendpayload.test.ts
+++ b/src/channels/plugins/outbound/direct-text-media.sendpayload.test.ts
@@ -1,9 +1,17 @@
-import { describe, expect, it, vi } from "vitest";
+import { describe, vi } from "vitest";
 import type { ReplyPayload } from "../../../auto-reply/types.js";
+import {
+  installSendPayloadContractSuite,
+  primeSendMock,
+} from "../../../test-utils/send-payload-contract.js";
 import { createDirectTextMediaOutbound } from "./direct-text-media.js";
 
-function makeOutbound() {
-  const sendFn = vi.fn().mockResolvedValue({ messageId: "m1" });
+function createDirectHarness(params: {
+  payload: ReplyPayload;
+  sendResults?: Array<{ messageId: string }>;
+}) {
+  const sendFn = vi.fn();
+  primeSendMock(sendFn, { messageId: "m1" }, params.sendResults);
   const outbound = createDirectTextMediaOutbound({
     channel: "imessage",
     resolveSender: () => sendFn,
@@ -24,94 +32,16 @@ function baseCtx(payload: ReplyPayload) {
 }
 
 describe("createDirectTextMediaOutbound sendPayload", () => {
-  it("text-only delegates to sendText", async () => {
-    const { outbound, sendFn } = makeOutbound();
-    const result = await outbound.sendPayload!(baseCtx({ text: "hello" }));
-
-    expect(sendFn).toHaveBeenCalledTimes(1);
-    expect(sendFn).toHaveBeenCalledWith("user1", "hello", expect.any(Object));
-    expect(result).toMatchObject({ channel: "imessage", messageId: "m1" });
-  });
-
-  it("single media delegates to sendMedia", async () => {
-    const { outbound, sendFn } = makeOutbound();
-    const result = await outbound.sendPayload!(
-      baseCtx({ text: "cap", mediaUrl: "https://example.com/a.jpg" }),
-    );
-
-    expect(sendFn).toHaveBeenCalledTimes(1);
-    expect(sendFn).toHaveBeenCalledWith(
-      "user1",
-      "cap",
-      expect.objectContaining({ mediaUrl: "https://example.com/a.jpg" }),
-    );
-    expect(result).toMatchObject({ channel: "imessage", messageId: "m1" });
-  });
-
-  it("multi-media iterates URLs with caption on first", async () => {
-    const sendFn = vi
-      .fn()
-      .mockResolvedValueOnce({ messageId: "m1" })
-      .mockResolvedValueOnce({ messageId: "m2" });
-    const outbound = createDirectTextMediaOutbound({
-      channel: "imessage",
-      resolveSender: () => sendFn,
-      resolveMaxBytes: () => undefined,
-      buildTextOptions: (opts) => opts as never,
-      buildMediaOptions: (opts) => opts as never,
-    });
-    const result = await outbound.sendPayload!(
-      baseCtx({
-        text: "caption",
-        mediaUrls: ["https://example.com/1.jpg", "https://example.com/2.jpg"],
-      }),
-    );
-
-    expect(sendFn).toHaveBeenCalledTimes(2);
-    expect(sendFn).toHaveBeenNthCalledWith(
-      1,
-      "user1",
-      "caption",
-      expect.objectContaining({ mediaUrl: "https://example.com/1.jpg" }),
-    );
-    expect(sendFn).toHaveBeenNthCalledWith(
-      2,
-      "user1",
-      "",
-      expect.objectContaining({ mediaUrl: "https://example.com/2.jpg" }),
-    );
-    expect(result).toMatchObject({ channel: "imessage", messageId: "m2" });
-  });
-
-  it("empty payload returns no-op", async () => {
-    const { outbound, sendFn } = makeOutbound();
-    const result = await outbound.sendPayload!(baseCtx({}));
-
-    expect(sendFn).not.toHaveBeenCalled();
-    expect(result).toEqual({ channel: "imessage", messageId: "" });
-  });
-
-  it("chunking splits long text", async () => {
-    const sendFn = vi
-      .fn()
-      .mockResolvedValueOnce({ messageId: "c1" })
-      .mockResolvedValueOnce({ messageId: "c2" });
-    const outbound = createDirectTextMediaOutbound({
-      channel: "signal",
-      resolveSender: () => sendFn,
-      resolveMaxBytes: () => undefined,
-      buildTextOptions: (opts) => opts as never,
-      buildMediaOptions: (opts) => opts as never,
-    });
-    // textChunkLimit is 4000; generate text exceeding that
-    const longText = "a".repeat(5000);
-    const result = await outbound.sendPayload!(baseCtx({ text: longText }));
-
-    expect(sendFn.mock.calls.length).toBeGreaterThanOrEqual(2);
-    // Each chunk should be within the limit
-    for (const call of sendFn.mock.calls) {
-      expect((call[1] as string).length).toBeLessThanOrEqual(4000);
-    }
-    expect(result).toMatchObject({ channel: "signal" });
+  installSendPayloadContractSuite({
+    channel: "imessage",
+    chunking: { mode: "split", longTextLength: 5000, maxChunkLength: 4000 },
+    createHarness: ({ payload, sendResults }) => {
+      const { outbound, sendFn } = createDirectHarness({ payload, sendResults });
+      return {
+        run: async () => await outbound.sendPayload!(baseCtx(payload)),
+        sendMock: sendFn,
+        to: "user1",
+      };
+    },
   });
 });
diff --git a/src/channels/plugins/outbound/discord.sendpayload.test.ts b/src/channels/plugins/outbound/discord.sendpayload.test.ts
index 07c821d6e79..168f8d8d927 100644
--- a/src/channels/plugins/outbound/discord.sendpayload.test.ts
+++ b/src/channels/plugins/outbound/discord.sendpayload.test.ts
@@ -1,98 +1,37 @@
-import { describe, expect, it, vi } from "vitest";
+import { describe, vi } from "vitest";
 import type { ReplyPayload } from "../../../auto-reply/types.js";
+import {
+  installSendPayloadContractSuite,
+  primeSendMock,
+} from "../../../test-utils/send-payload-contract.js";
 import { discordOutbound } from "./discord.js";
 
-function baseCtx(payload: ReplyPayload) {
-  return {
+function createHarness(params: {
+  payload: ReplyPayload;
+  sendResults?: Array<{ messageId: string }>;
+}) {
+  const sendDiscord = vi.fn();
+  primeSendMock(sendDiscord, { messageId: "dc-1", channelId: "123456" }, params.sendResults);
+  const ctx = {
     cfg: {},
     to: "channel:123456",
     text: "",
-    payload,
+    payload: params.payload,
     deps: {
-      sendDiscord: vi.fn().mockResolvedValue({ messageId: "dc-1", channelId: "123456" }),
+      sendDiscord,
     },
   };
+  return {
+    run: async () => await discordOutbound.sendPayload!(ctx),
+    sendMock: sendDiscord,
+    to: ctx.to,
+  };
 }
 
 describe("discordOutbound sendPayload", () => {
-  it("text-only delegates to sendText", async () => {
-    const ctx = baseCtx({ text: "hello" });
-    const result = await discordOutbound.sendPayload!(ctx);
-
-    expect(ctx.deps.sendDiscord).toHaveBeenCalledTimes(1);
-    expect(ctx.deps.sendDiscord).toHaveBeenCalledWith(
-      "channel:123456",
-      "hello",
-      expect.any(Object),
-    );
-    expect(result).toMatchObject({ channel: "discord" });
-  });
-
-  it("single media delegates to sendMedia", async () => {
-    const ctx = baseCtx({ text: "cap", mediaUrl: "https://example.com/a.jpg" });
-    const result = await discordOutbound.sendPayload!(ctx);
-
-    expect(ctx.deps.sendDiscord).toHaveBeenCalledTimes(1);
-    expect(ctx.deps.sendDiscord).toHaveBeenCalledWith(
-      "channel:123456",
-      "cap",
-      expect.objectContaining({ mediaUrl: "https://example.com/a.jpg" }),
-    );
-    expect(result).toMatchObject({ channel: "discord" });
-  });
-
-  it("multi-media iterates URLs with caption on first", async () => {
-    const sendDiscord = vi
-      .fn()
-      .mockResolvedValueOnce({ messageId: "dc-1", channelId: "123456" })
-      .mockResolvedValueOnce({ messageId: "dc-2", channelId: "123456" });
-    const ctx = {
-      cfg: {},
-      to: "channel:123456",
-      text: "",
-      payload: {
-        text: "caption",
-        mediaUrls: ["https://example.com/1.jpg", "https://example.com/2.jpg"],
-      } as ReplyPayload,
-      deps: { sendDiscord },
-    };
-    const result = await discordOutbound.sendPayload!(ctx);
-
-    expect(sendDiscord).toHaveBeenCalledTimes(2);
-    expect(sendDiscord).toHaveBeenNthCalledWith(
-      1,
-      "channel:123456",
-      "caption",
-      expect.objectContaining({ mediaUrl: "https://example.com/1.jpg" }),
-    );
-    expect(sendDiscord).toHaveBeenNthCalledWith(
-      2,
-      "channel:123456",
-      "",
-      expect.objectContaining({ mediaUrl: "https://example.com/2.jpg" }),
-    );
-    expect(result).toMatchObject({ channel: "discord", messageId: "dc-2" });
-  });
-
-  it("empty payload returns no-op", async () => {
-    const ctx = baseCtx({});
-    const result = await discordOutbound.sendPayload!(ctx);
-
-    expect(ctx.deps.sendDiscord).not.toHaveBeenCalled();
-    expect(result).toEqual({ channel: "discord", messageId: "" });
-  });
-
-  it("text exceeding chunk limit is sent as-is when chunker is null", async () => {
-    // Discord has chunker: null, so long text should be sent as a single message
-    const ctx = baseCtx({ text: "a".repeat(3000) });
-    const result = await discordOutbound.sendPayload!(ctx);
-
-    expect(ctx.deps.sendDiscord).toHaveBeenCalledTimes(1);
-    expect(ctx.deps.sendDiscord).toHaveBeenCalledWith(
-      "channel:123456",
-      "a".repeat(3000),
-      expect.any(Object),
-    );
-    expect(result).toMatchObject({ channel: "discord" });
+  installSendPayloadContractSuite({
+    channel: "discord",
+    chunking: { mode: "passthrough", longTextLength: 3000 },
+    createHarness,
   });
 });
diff --git a/src/channels/plugins/outbound/slack.sendpayload.test.ts b/src/channels/plugins/outbound/slack.sendpayload.test.ts
index c6df264df12..374c9881a73 100644
--- a/src/channels/plugins/outbound/slack.sendpayload.test.ts
+++ b/src/channels/plugins/outbound/slack.sendpayload.test.ts
@@ -1,92 +1,41 @@
-import { describe, expect, it, vi } from "vitest";
+import { describe, vi } from "vitest";
 import type { ReplyPayload } from "../../../auto-reply/types.js";
+import {
+  installSendPayloadContractSuite,
+  primeSendMock,
+} from "../../../test-utils/send-payload-contract.js";
 import { slackOutbound } from "./slack.js";
 
-function baseCtx(payload: ReplyPayload) {
-  return {
+function createHarness(params: {
+  payload: ReplyPayload;
+  sendResults?: Array<{ messageId: string }>;
+}) {
+  const sendSlack = vi.fn();
+  primeSendMock(
+    sendSlack,
+    { messageId: "sl-1", channelId: "C12345", ts: "1234.5678" },
+    params.sendResults,
+  );
+  const ctx = {
     cfg: {},
     to: "C12345",
     text: "",
-    payload,
+    payload: params.payload,
     deps: {
-      sendSlack: vi
-        .fn()
-        .mockResolvedValue({ messageId: "sl-1", channelId: "C12345", ts: "1234.5678" }),
+      sendSlack,
     },
   };
+  return {
+    run: async () => await slackOutbound.sendPayload!(ctx),
+    sendMock: sendSlack,
+    to: ctx.to,
+  };
 }
 
 describe("slackOutbound sendPayload", () => {
-  it("text-only delegates to sendText", async () => {
-    const ctx = baseCtx({ text: "hello" });
-    const result = await slackOutbound.sendPayload!(ctx);
-
-    expect(ctx.deps.sendSlack).toHaveBeenCalledTimes(1);
-    expect(ctx.deps.sendSlack).toHaveBeenCalledWith("C12345", "hello", expect.any(Object));
-    expect(result).toMatchObject({ channel: "slack" });
-  });
-
-  it("single media delegates to sendMedia", async () => {
-    const ctx = baseCtx({ text: "cap", mediaUrl: "https://example.com/a.jpg" });
-    const result = await slackOutbound.sendPayload!(ctx);
-
-    expect(ctx.deps.sendSlack).toHaveBeenCalledTimes(1);
-    expect(ctx.deps.sendSlack).toHaveBeenCalledWith(
-      "C12345",
-      "cap",
-      expect.objectContaining({ mediaUrl: "https://example.com/a.jpg" }),
-    );
-    expect(result).toMatchObject({ channel: "slack" });
-  });
-
-  it("multi-media iterates URLs with caption on first", async () => {
-    const sendSlack = vi
-      .fn()
-      .mockResolvedValueOnce({ messageId: "sl-1", channelId: "C12345" })
-      .mockResolvedValueOnce({ messageId: "sl-2", channelId: "C12345" });
-    const ctx = {
-      cfg: {},
-      to: "C12345",
-      text: "",
-      payload: {
-        text: "caption",
-        mediaUrls: ["https://example.com/1.jpg", "https://example.com/2.jpg"],
-      } as ReplyPayload,
-      deps: { sendSlack },
-    };
-    const result = await slackOutbound.sendPayload!(ctx);
-
-    expect(sendSlack).toHaveBeenCalledTimes(2);
-    expect(sendSlack).toHaveBeenNthCalledWith(
-      1,
-      "C12345",
-      "caption",
-      expect.objectContaining({ mediaUrl: "https://example.com/1.jpg" }),
-    );
-    expect(sendSlack).toHaveBeenNthCalledWith(
-      2,
-      "C12345",
-      "",
-      expect.objectContaining({ mediaUrl: "https://example.com/2.jpg" }),
-    );
-    expect(result).toMatchObject({ channel: "slack", messageId: "sl-2" });
-  });
-
-  it("empty payload returns no-op", async () => {
-    const ctx = baseCtx({});
-    const result = await slackOutbound.sendPayload!(ctx);
-
-    expect(ctx.deps.sendSlack).not.toHaveBeenCalled();
-    expect(result).toEqual({ channel: "slack", messageId: "" });
-  });
-
-  it("text exceeding chunk limit is sent as-is when chunker is null", async () => {
-    // Slack has chunker: null, so long text should be sent as a single message
-    const ctx = baseCtx({ text: "a".repeat(5000) });
-    const result = await slackOutbound.sendPayload!(ctx);
-
-    expect(ctx.deps.sendSlack).toHaveBeenCalledTimes(1);
-    expect(ctx.deps.sendSlack).toHaveBeenCalledWith("C12345", "a".repeat(5000), expect.any(Object));
-    expect(result).toMatchObject({ channel: "slack" });
+  installSendPayloadContractSuite({
+    channel: "slack",
+    chunking: { mode: "passthrough", longTextLength: 5000 },
+    createHarness,
   });
 });
diff --git a/src/channels/plugins/outbound/whatsapp.sendpayload.test.ts b/src/channels/plugins/outbound/whatsapp.sendpayload.test.ts
index 3eb6f7467dc..e98351cfa61 100644
--- a/src/channels/plugins/outbound/whatsapp.sendpayload.test.ts
+++ b/src/channels/plugins/outbound/whatsapp.sendpayload.test.ts
@@ -1,106 +1,37 @@
-import { describe, expect, it, vi } from "vitest";
+import { describe, vi } from "vitest";
 import type { ReplyPayload } from "../../../auto-reply/types.js";
+import {
+  installSendPayloadContractSuite,
+  primeSendMock,
+} from "../../../test-utils/send-payload-contract.js";
 import { whatsappOutbound } from "./whatsapp.js";
 
-function baseCtx(payload: ReplyPayload) {
-  return {
+function createHarness(params: {
+  payload: ReplyPayload;
+  sendResults?: Array<{ messageId: string }>;
+}) {
+  const sendWhatsApp = vi.fn();
+  primeSendMock(sendWhatsApp, { messageId: "wa-1" }, params.sendResults);
+  const ctx = {
     cfg: {},
     to: "5511999999999@c.us",
     text: "",
-    payload,
+    payload: params.payload,
     deps: {
-      sendWhatsApp: vi.fn().mockResolvedValue({ messageId: "wa-1" }),
+      sendWhatsApp,
     },
   };
+  return {
+    run: async () => await whatsappOutbound.sendPayload!(ctx),
+    sendMock: sendWhatsApp,
+    to: ctx.to,
+  };
 }
 
 describe("whatsappOutbound sendPayload", () => {
-  it("text-only delegates to sendText", async () => {
-    const ctx = baseCtx({ text: "hello" });
-    const result = await whatsappOutbound.sendPayload!(ctx);
-
-    expect(ctx.deps.sendWhatsApp).toHaveBeenCalledTimes(1);
-    expect(ctx.deps.sendWhatsApp).toHaveBeenCalledWith(
-      "5511999999999@c.us",
-      "hello",
-      expect.any(Object),
-    );
-    expect(result).toMatchObject({ channel: "whatsapp", messageId: "wa-1" });
-  });
-
-  it("single media delegates to sendMedia", async () => {
-    const ctx = baseCtx({ text: "cap", mediaUrl: "https://example.com/a.jpg" });
-    const result = await whatsappOutbound.sendPayload!(ctx);
-
-    expect(ctx.deps.sendWhatsApp).toHaveBeenCalledTimes(1);
-    expect(ctx.deps.sendWhatsApp).toHaveBeenCalledWith(
-      "5511999999999@c.us",
-      "cap",
-      expect.objectContaining({ mediaUrl: "https://example.com/a.jpg" }),
-    );
-    expect(result).toMatchObject({ channel: "whatsapp" });
-  });
-
-  it("multi-media iterates URLs with caption on first", async () => {
-    const sendWhatsApp = vi
-      .fn()
-      .mockResolvedValueOnce({ messageId: "wa-1" })
-      .mockResolvedValueOnce({ messageId: "wa-2" });
-    const ctx = {
-      cfg: {},
-      to: "5511999999999@c.us",
-      text: "",
-      payload: {
-        text: "caption",
-        mediaUrls: ["https://example.com/1.jpg", "https://example.com/2.jpg"],
-      } as ReplyPayload,
-      deps: { sendWhatsApp },
-    };
-    const result = await whatsappOutbound.sendPayload!(ctx);
-
-    expect(sendWhatsApp).toHaveBeenCalledTimes(2);
-    expect(sendWhatsApp).toHaveBeenNthCalledWith(
-      1,
-      "5511999999999@c.us",
-      "caption",
-      expect.objectContaining({ mediaUrl: "https://example.com/1.jpg" }),
-    );
-    expect(sendWhatsApp).toHaveBeenNthCalledWith(
-      2,
-      "5511999999999@c.us",
-      "",
-      expect.objectContaining({ mediaUrl: "https://example.com/2.jpg" }),
-    );
-    expect(result).toMatchObject({ channel: "whatsapp", messageId: "wa-2" });
-  });
-
-  it("empty payload returns no-op", async () => {
-    const ctx = baseCtx({});
-    const result = await whatsappOutbound.sendPayload!(ctx);
-
-    expect(ctx.deps.sendWhatsApp).not.toHaveBeenCalled();
-    expect(result).toEqual({ channel: "whatsapp", messageId: "" });
-  });
-
-  it("chunking splits long text", async () => {
-    const sendWhatsApp = vi
-      .fn()
-      .mockResolvedValueOnce({ messageId: "wa-c1" })
-      .mockResolvedValueOnce({ messageId: "wa-c2" });
-    const longText = "a".repeat(5000);
-    const ctx = {
-      cfg: {},
-      to: "5511999999999@c.us",
-      text: "",
-      payload: { text: longText } as ReplyPayload,
-      deps: { sendWhatsApp },
-    };
-    const result = await whatsappOutbound.sendPayload!(ctx);
-
-    expect(sendWhatsApp.mock.calls.length).toBeGreaterThanOrEqual(2);
-    for (const call of sendWhatsApp.mock.calls) {
-      expect((call[1] as string).length).toBeLessThanOrEqual(4000);
-    }
-    expect(result).toMatchObject({ channel: "whatsapp" });
+  installSendPayloadContractSuite({
+    channel: "whatsapp",
+    chunking: { mode: "split", longTextLength: 5000, maxChunkLength: 4000 },
+    createHarness,
   });
 });
diff --git a/src/test-utils/send-payload-contract.ts b/src/test-utils/send-payload-contract.ts
new file mode 100644
index 00000000000..5e78e406a74
--- /dev/null
+++ b/src/test-utils/send-payload-contract.ts
@@ -0,0 +1,138 @@
+import { expect, it, type Mock } from "vitest";
+
+type PayloadLike = {
+  mediaUrl?: string;
+  mediaUrls?: string[];
+  text?: string;
+};
+
+type SendResultLike = {
+  messageId: string;
+  [key: string]: unknown;
+};
+
+type ChunkingMode =
+  | {
+      longTextLength: number;
+      maxChunkLength: number;
+      mode: "split";
+    }
+  | {
+      longTextLength: number;
+      mode: "passthrough";
+    };
+
+export function installSendPayloadContractSuite(params: {
+  channel: string;
+  chunking: ChunkingMode;
+  createHarness: (params: { payload: PayloadLike; sendResults?: SendResultLike[] }) => {
+    run: () => Promise<Record<string, unknown>>;
+    sendMock: Mock;
+    to: string;
+  };
+}) {
+  it("text-only delegates to sendText", async () => {
+    const { run, sendMock, to } = params.createHarness({
+      payload: { text: "hello" },
+    });
+    const result = await run();
+
+    expect(sendMock).toHaveBeenCalledTimes(1);
+    expect(sendMock).toHaveBeenCalledWith(to, "hello", expect.any(Object));
+    expect(result).toMatchObject({ channel: params.channel });
+  });
+
+  it("single media delegates to sendMedia", async () => {
+    const { run, sendMock, to } = params.createHarness({
+      payload: { text: "cap", mediaUrl: "https://example.com/a.jpg" },
+    });
+    const result = await run();
+
+    expect(sendMock).toHaveBeenCalledTimes(1);
+    expect(sendMock).toHaveBeenCalledWith(
+      to,
+      "cap",
+      expect.objectContaining({ mediaUrl: "https://example.com/a.jpg" }),
+    );
+    expect(result).toMatchObject({ channel: params.channel });
+  });
+
+  it("multi-media iterates URLs with caption on first", async () => {
+    const { run, sendMock, to } = params.createHarness({
+      payload: {
+        text: "caption",
+        mediaUrls: ["https://example.com/1.jpg", "https://example.com/2.jpg"],
+      },
+      sendResults: [{ messageId: "m-1" }, { messageId: "m-2" }],
+    });
+    const result = await run();
+
+    expect(sendMock).toHaveBeenCalledTimes(2);
+    expect(sendMock).toHaveBeenNthCalledWith(
+      1,
+      to,
+      "caption",
+      expect.objectContaining({ mediaUrl: "https://example.com/1.jpg" }),
+    );
+    expect(sendMock).toHaveBeenNthCalledWith(
+      2,
+      to,
+      "",
+      expect.objectContaining({ mediaUrl: "https://example.com/2.jpg" }),
+    );
+    expect(result).toMatchObject({ channel: params.channel, messageId: "m-2" });
+  });
+
+  it("empty payload returns no-op", async () => {
+    const { run, sendMock } = params.createHarness({ payload: {} });
+    const result = await run();
+
+    expect(sendMock).not.toHaveBeenCalled();
+    expect(result).toEqual({ channel: params.channel, messageId: "" });
+  });
+
+  if (params.chunking.mode === "passthrough") {
+    it("text exceeding chunk limit is sent as-is when chunker is null", async () => {
+      const text = "a".repeat(params.chunking.longTextLength);
+      const { run, sendMock, to } = params.createHarness({ payload: { text } });
+      const result = await run();
+
+      expect(sendMock).toHaveBeenCalledTimes(1);
+      expect(sendMock).toHaveBeenCalledWith(to, text, expect.any(Object));
+      expect(result).toMatchObject({ channel: params.channel });
+    });
+    return;
+  }
+
+  const chunking = params.chunking;
+
+  it("chunking splits long text", async () => {
+    const text = "a".repeat(chunking.longTextLength);
+    const { run, sendMock } = params.createHarness({
+      payload: { text },
+      sendResults: [{ messageId: "c-1" }, { messageId: "c-2" }],
+    });
+    const result = await run();
+
+    expect(sendMock.mock.calls.length).toBeGreaterThanOrEqual(2);
+    for (const call of sendMock.mock.calls) {
+      expect((call[1] as string).length).toBeLessThanOrEqual(chunking.maxChunkLength);
+    }
+    expect(result).toMatchObject({ channel: params.channel });
+  });
+}
+
+export function primeSendMock(
+  sendMock: Mock,
+  fallbackResult: Record<string, unknown>,
+  sendResults: SendResultLike[] = [],
+) {
+  sendMock.mockReset();
+  if (sendResults.length === 0) {
+    sendMock.mockResolvedValue(fallbackResult);
+    return;
+  }
+  for (const result of sendResults) {
+    sendMock.mockResolvedValueOnce(result);
+  }
+}