diff --git a/extensions/matrix/src/matrix/monitor/handler.test.ts b/extensions/matrix/src/matrix/monitor/handler.test.ts
index 073da131a27..6a2c30414bd 100644
--- a/extensions/matrix/src/matrix/monitor/handler.test.ts
+++ b/extensions/matrix/src/matrix/monitor/handler.test.ts
@@ -3185,6 +3185,31 @@ describe("matrix monitor handler draft streaming", () => {
     await finish();
   });
 
+  it("keeps truncated Matrix tool progress UTF-16 safe", async () => {
+    const { dispatch } = createStreamingHarness({
+      streaming: "progress",
+      previewToolProgressEnabled: true,
+      accountConfig: {
+        streaming: {
+          mode: "progress",
+          progress: { label: false, maxLineChars: 500 },
+        },
+      } as never,
+    });
+    const { opts, finish } = await dispatch();
+    const progressPrefix = "x".repeat(298);
+
+    const progressText = `${progressPrefix}🎉tail`;
+    await opts.onItemEvent?.({ progressText });
+    await opts.onItemEvent?.({ progressText });
+
+    await vi.waitFor(() => {
+      expect(sendSingleTextMessageMatrixMock).toHaveBeenCalledTimes(1);
+    });
+    expect(singleTextMessageBody()).toBe(`- \`${progressPrefix}...\``);
+    await finish();
+  });
+
   it("replaces recovered Matrix command progress instead of leaving stale failed text", async () => {
     const { dispatch } = createStreamingHarness({
       streaming: "progress",
diff --git a/extensions/matrix/src/matrix/monitor/handler.ts b/extensions/matrix/src/matrix/monitor/handler.ts
index 49243ed79a8..0386c7f56a0 100644
--- a/extensions/matrix/src/matrix/monitor/handler.ts
+++ b/extensions/matrix/src/matrix/monitor/handler.ts
@@ -44,6 +44,7 @@ import { resolveInboundLastRouteSessionKey } from "openclaw/plugin-sdk/routing";
 import { resolvePinnedMainDmOwnerFromAllowlist } from "openclaw/plugin-sdk/security-runtime";
 import { getSessionEntry } from "openclaw/plugin-sdk/session-store-runtime";
 import { normalizeOptionalString } from "openclaw/plugin-sdk/string-coerce-runtime";
+import { truncateUtf16Safe } from "openclaw/plugin-sdk/text-utility-runtime";
 import type {
   CoreConfig,
   MatrixConfig,
@@ -434,7 +435,7 @@ function formatMatrixToolProgressMarkdownCode(text: string): string {
   const clipped =
     text.length <= MATRIX_TOOL_PROGRESS_MAX_CHARS
       ? text
-      : `${text.slice(0, MATRIX_TOOL_PROGRESS_MAX_CHARS - 1).trimEnd()}...`;
+      : `${truncateUtf16Safe(text, MATRIX_TOOL_PROGRESS_MAX_CHARS - 1).trimEnd()}...`;
   const safe = clipped.replaceAll("`", "'");
   return `\`${safe}\``;
 }
diff --git a/extensions/matrix/src/matrix/sdk/event-helpers.test.ts b/extensions/matrix/src/matrix/sdk/event-helpers.test.ts
index 6b259835ba7..c187cc893c5 100644
--- a/extensions/matrix/src/matrix/sdk/event-helpers.test.ts
+++ b/extensions/matrix/src/matrix/sdk/event-helpers.test.ts
@@ -41,6 +41,14 @@ describe("event-helpers", () => {
     expect(fromText.statusCode).toBe(500);
   });
 
+  it("keeps truncated HTTP error bodies UTF-16 safe", () => {
+    const parsedPrefix = `{"detail":"${"a".repeat(488)}`;
+    const invalidPrefix = `not-json ${"b".repeat(490)}`;
+
+    expect(buildHttpError(500, `${parsedPrefix}😀"}`).message).toBe(parsedPrefix);
+    expect(buildHttpError(502, `${invalidPrefix}🎉tail`).message).toBe(invalidPrefix);
+  });
+
   it("serializes Matrix events and resolves state key from available sources", () => {
     const viaGetter = {
       getId: () => "$1",
diff --git a/extensions/matrix/src/matrix/sdk/event-helpers.ts b/extensions/matrix/src/matrix/sdk/event-helpers.ts
index 61047096a2b..06018408a27 100644
--- a/extensions/matrix/src/matrix/sdk/event-helpers.ts
+++ b/extensions/matrix/src/matrix/sdk/event-helpers.ts
@@ -1,5 +1,6 @@
 // Matrix helper module supports event helpers behavior.
 import type { MatrixEvent } from "matrix-js-sdk/lib/matrix.js";
+import { truncateUtf16Safe } from "openclaw/plugin-sdk/text-utility-runtime";
 import type { MatrixRawEvent } from "./types.js";
 
 type MatrixEventContentMode = "current" | "original";
@@ -90,10 +91,10 @@ export function buildHttpError(
       if (typeof parsed.error === "string" && parsed.error.trim()) {
         message = parsed.error.trim();
       } else {
-        message = bodyText.slice(0, 500);
+        message = truncateUtf16Safe(bodyText, 500);
       }
     } catch {
-      message = bodyText.slice(0, 500);
+      message = truncateUtf16Safe(bodyText, 500);
     }
   }
   return Object.assign(new Error(message), { statusCode });