fix(mistral): use truncateUtf16Safe for error text truncation (#102539)

lsr911 · claude · steipete · web-flow · commit 3ac7729f4c5f · 2026-07-09T10:03:51.000+01:00
* fix(mistral): use truncateUtf16Safe for error text truncation

Replace naive .slice(0, maxChars) with truncateUtf16Safe() in
truncateErrorText() to prevent surrogate pair splitting in
Mistral provider error messages shown to users.

Co-Authored-By: Claude &lt;noreply@anthropic.com&gt;

* fix(ai): keep Mistral errors UTF-16 safe

---------

Co-authored-by: Claude &lt;noreply@anthropic.com&gt;
Co-authored-by: Peter Steinberger &lt;steipete@gmail.com&gt;
diff --git a/packages/ai/src/providers/mistral.test.ts b/packages/ai/src/providers/mistral.test.ts
@@ -7,6 +7,7 @@ import { SYSTEM_PROMPT_CACHE_BOUNDARY } from "../utils/system-prompt-cache-bound
 const mistralMockState = vi.hoisted(() => ({
   configs: [] as unknown[],
   payloads: [] as unknown[],
+  streamError: new Error("stop before network") as unknown,
 }));
 
 vi.mock("@mistralai/mistralai", async () => {
@@ -27,7 +28,7 @@ vi.mock("@mistralai/mistralai", async () => {
       chat = {
         stream: vi.fn(async (payload: unknown) => {
           mistralMockState.payloads.push(payload);
-          throw new Error("stop before network");
+          throw mistralMockState.streamError;
         }),
       };
     },
@@ -77,6 +78,7 @@ describe("Mistral provider", () => {
   beforeEach(() => {
     mistralMockState.configs = [];
     mistralMockState.payloads = [];
+    mistralMockState.streamError = new Error("stop before network");
   });
 
   afterEach(() => {
@@ -95,6 +97,20 @@ describe("Mistral provider", () => {
     expect((mistralMockState.payloads[0] as { stop?: unknown }).stop).toEqual(["STOP"]);
   });
 
+  it("keeps truncated Mistral error bodies UTF-16 safe with an exact omitted count", async () => {
+    const prefix = "a".repeat(3_999);
+    mistralMockState.streamError = Object.assign(new Error("invalid request"), {
+      statusCode: 400,
+      body: `${prefix}😀tail`,
+    });
+
+    const result = await streamMistral(makeMistralModel(), context, {
+      apiKey: "sk-mistral-provider",
+    }).result();
+
+    expect(result.errorMessage).toBe(`Mistral API error (400): ${prefix}... [truncated 6 chars]`);
+  });
+
   it("routes the Mistral HTTPClient through the host guarded fetch", async () => {
     const hostFetch = vi.fn<typeof fetch>(async () => new Response("guarded"));
     configureAiTransportHost({ buildModelFetch: () => hostFetch });
diff --git a/packages/ai/src/providers/mistral.ts b/packages/ai/src/providers/mistral.ts
@@ -7,6 +7,7 @@ import type {
   ContentChunk,
   FunctionTool,
 } from "@mistralai/mistralai/models/components";
+import { truncateUtf16Safe } from "@openclaw/normalization-core/utf16-slice";
 import { getEnvApiKey } from "../env-api-keys.js";
 import { getAiTransportHost } from "../host.js";
 import { calculateCost, clampThinkingLevel } from "../model-utils.js";
@@ -295,7 +296,8 @@ function truncateErrorText(text: string, maxChars: number): string {
   if (text.length <= maxChars) {
     return text;
   }
-  return `${text.slice(0, maxChars)}... [truncated ${text.length - maxChars} chars]`;
+  const truncated = truncateUtf16Safe(text, maxChars);
+  return `${truncated}... [truncated ${text.length - truncated.length} chars]`;
 }
 
 function safeJsonStringify(value: unknown): string {
