diff --git a/extensions/imessage/src/actions.test.ts b/extensions/imessage/src/actions.test.ts
index 4ec116eefedb..b521b737853c 100644
--- a/extensions/imessage/src/actions.test.ts
+++ b/extensions/imessage/src/actions.test.ts
@@ -304,6 +304,52 @@ describe("imessage message actions", () => {
     ]);
   });
 
+  it("rejects fractional chatId params before resolving chat GUIDs", async () => {
+    probeMock.getCachedIMessagePrivateApiStatus.mockReturnValue({
+      available: true,
+      v2Ready: true,
+      selectors: {},
+    });
+
+    await expect(
+      imessageMessageActions.handleAction?.({
+        action: "react",
+        cfg: cfg(),
+        params: {
+          chatId: 42.5,
+          messageId: "message-guid",
+          emoji: "👍",
+        },
+      } as never),
+    ).rejects.toThrow("chatId must be a positive integer");
+
+    expect(runtimeMock.resolveChatGuidForTarget).not.toHaveBeenCalled();
+    expect(runtimeMock.sendReaction).not.toHaveBeenCalled();
+  });
+
+  it("rejects fractional partIndex values before invoking bridge actions", async () => {
+    probeMock.getCachedIMessagePrivateApiStatus.mockReturnValue({
+      available: true,
+      v2Ready: true,
+      selectors: {},
+    });
+
+    await expect(
+      imessageMessageActions.handleAction?.({
+        action: "react",
+        cfg: cfg(),
+        params: {
+          chatGuid: "iMessage;+;chat0000",
+          messageId: "message-guid",
+          emoji: "👍",
+          partIndex: 1.5,
+        },
+      } as never),
+    ).rejects.toThrow("partIndex must be a non-negative integer");
+
+    expect(runtimeMock.sendReaction).not.toHaveBeenCalled();
+  });
+
   it("resolves short message ids before invoking bridge actions", async () => {
     probeMock.getCachedIMessagePrivateApiStatus.mockReturnValue({
       available: true,
diff --git a/extensions/imessage/src/actions.ts b/extensions/imessage/src/actions.ts
index aa3a534a1c72..c725730e8a2a 100644
--- a/extensions/imessage/src/actions.ts
+++ b/extensions/imessage/src/actions.ts
@@ -2,7 +2,8 @@ import { readBooleanParam } from "openclaw/plugin-sdk/boolean-param";
 import {
   createActionGate,
   jsonResult,
-  readNumberParam,
+  readNonNegativeIntegerParam,
+  readPositiveIntegerParam,
   readReactionParams,
   readStringParam,
 } from "openclaw/plugin-sdk/channel-actions";
@@ -103,7 +104,7 @@ async function resolveChatGuid(params: {
   if (explicitChatGuid) {
     return explicitChatGuid;
   }
-  const explicitChatId = readNumberParam(params.actionParams, "chatId", { integer: true });
+  const explicitChatId = readPositiveIntegerParam(params.actionParams, "chatId");
   if (typeof explicitChatId === "number") {
     const resolved = await params.runtime.resolveChatGuidForTarget({
       target: { kind: "chat_id", chatId: explicitChatId },
@@ -198,7 +199,7 @@ function buildChatContextFromActionParams(params: {
 }): IMessageChatContext {
   const explicitChatGuid = readStringParam(params.actionParams, "chatGuid")?.trim();
   const explicitChatIdentifier = readStringParam(params.actionParams, "chatIdentifier")?.trim();
-  const explicitChatId = readNumberParam(params.actionParams, "chatId", { integer: true });
+  const explicitChatId = readPositiveIntegerParam(params.actionParams, "chatId");
   // Trim before the truthy check so a whitespace-only currentChannelId can't
   // reach parseIMessageTarget (which throws on empty/whitespace input and
   // would abort the whole action with a confusing "target is required").
@@ -486,7 +487,7 @@ export const imessageMessageActions: ChannelMessageActionAdapter = {
         );
       }
       const resolvedMessageId = messageId();
-      const partIndex = readNumberParam(params, "partIndex", { integer: true });
+      const partIndex = readNonNegativeIntegerParam(params, "partIndex");
       const resolvedChatGuid = await chatGuid();
       const reactionsToSend = remove && !reaction ? [...TAPBACK_KINDS] : reaction ? [reaction] : [];
       for (const kind of reactionsToSend) {
@@ -512,7 +513,7 @@ export const imessageMessageActions: ChannelMessageActionAdapter = {
       if (!text) {
         throw new Error("iMessage edit requires text, newText, or message.");
       }
-      const partIndex = readNumberParam(params, "partIndex", { integer: true });
+      const partIndex = readNonNegativeIntegerParam(params, "partIndex");
       const backwardsCompatMessage = readStringParam(params, "backwardsCompatMessage");
       const resolvedChatGuid = await chatGuid();
       await runtime.editMessage({
@@ -529,7 +530,7 @@ export const imessageMessageActions: ChannelMessageActionAdapter = {
     if (action === "unsend") {
       await assertPrivateApiEnabled();
       const resolvedMessageId = messageId({ requireFromMe: true });
-      const partIndex = readNumberParam(params, "partIndex", { integer: true });
+      const partIndex = readNonNegativeIntegerParam(params, "partIndex");
       const resolvedChatGuid = await chatGuid();
       await runtime.unsendMessage({
         chatGuid: resolvedChatGuid,
@@ -569,7 +570,7 @@ export const imessageMessageActions: ChannelMessageActionAdapter = {
           );
         }
       }
-      const partIndex = readNumberParam(params, "partIndex", { integer: true });
+      const partIndex = readNonNegativeIntegerParam(params, "partIndex");
       const resolvedChatGuid = await chatGuid();
       const result = await runtime.sendRichMessage({
         chatGuid: resolvedChatGuid,