diff --git a/apps/desktop/src/components/objects/ObjectBrowser.vue b/apps/desktop/src/components/objects/ObjectBrowser.vue
index 93b04f5a6..f78dc3810 100644
--- a/apps/desktop/src/components/objects/ObjectBrowser.vue
+++ b/apps/desktop/src/components/objects/ObjectBrowser.vue
@@ -2405,7 +2405,7 @@ async function loadObjects(options?: { allowCached?: boolean }) {
     void loadObjectStatistics(request, cacheWriteToken, cachedAt);
   } catch (e: any) {
     if (!objectBrowserRowsLoadGuard.isCurrent(request)) return;
-    error.value = e?.message || String(e);
+    error.value = translateBackendError(t, e);
   } finally {
     if (objectBrowserRowsLoadGuard.isCurrent(request)) finishObjectBrowserRowsLoad();
   }
diff --git a/apps/desktop/src/components/sidebar/SidebarTreeRuntimeHost.vue b/apps/desktop/src/components/sidebar/SidebarTreeRuntimeHost.vue
index 86c83743d..42ca4dfc0 100644
--- a/apps/desktop/src/components/sidebar/SidebarTreeRuntimeHost.vue
+++ b/apps/desktop/src/components/sidebar/SidebarTreeRuntimeHost.vue
@@ -720,7 +720,7 @@ async function toggle() {
     if (!wasExpanded) node.isExpanded = false;
     const errMsg = e?.message || String(e);
     if (errMsg.includes(CONNECTION_ATTEMPT_CANCELLED_MESSAGE)) return;
-    toast(t("connection.connectFailed", { message: translateBackendError(t, errMsg) }), 5000);
+    toast(t("connection.connectFailed", { message: translateBackendError(t, e) }), 5000);
     openDriverStoreForInstallError(errMsg);
   }
 }
diff --git a/apps/desktop/src/i18n/__tests__/backendErrors.spec.ts b/apps/desktop/src/i18n/__tests__/backendErrors.spec.ts
index ac2f0af14..e47d427ab 100644
--- a/apps/desktop/src/i18n/__tests__/backendErrors.spec.ts
+++ b/apps/desktop/src/i18n/__tests__/backendErrors.spec.ts
@@ -2,7 +2,7 @@ import { readFileSync } from "node:fs";
 import { describe, expect, it as test } from "vitest";
 import { createI18n } from "vue-i18n";
 import { translateBackendError, type BackendErrorTranslate } from "@/i18n/backend-errors";
-import { BackendErrorException, normalizeBackendError } from "@/lib/backend/errorUtils";
+import { BackendErrorException, formatError, normalizeBackendError, sanitizeBackendErrorMessage } from "@/lib/backend/errorUtils";
 import en from "@/i18n/locales/en";
 import es from "@/i18n/locales/es";
 import it from "@/i18n/locales/it";
@@ -171,6 +171,23 @@ describe("backend error translation", () => {
     expect(translateBackendError(t, "some driver specific failure")).toBe("some driver specific failure");
   });
 
+  test("hides internal Agent error data from user-facing messages", () => {
+    const t = translatorFor("zh-CN");
+    const message = 'Agent RPC error (-1): driver: bad connection\nDBX_AGENT_ERROR_DATA:{"category":null,"retryable":null,"sessionDisposition":null,"stage":null,"operationOutcome":null,"agentSessionId":"e1a4d0a2907947b8adf31abb10c4dff9"}';
+    const expected = "Agent RPC error (-1): driver: bad connection";
+
+    expect(sanitizeBackendErrorMessage(message)).toBe(expected);
+    expect(formatError(new Error(message))).toBe(expected);
+    expect(new BackendErrorException(message).message).toBe(expected);
+    expect(translateBackendError(t, message)).toBe(expected);
+  });
+
+  test("preserves marker-like database messages without valid internal data", () => {
+    const message = "database returned\nDBX_AGENT_ERROR_DATA:not-json";
+
+    expect(sanitizeBackendErrorMessage(message)).toBe(message);
+  });
+
   test("normalizes Error and structural message objects before translation", () => {
     const t = translatorFor("zh-CN");
     const message = "file does not exist: /tmp/missing.sqlite";
@@ -213,6 +230,22 @@ describe("backend error translation", () => {
     expect(translateBackendError(t, error)).toBe(`${t(error.messageKey)}\n\n${error.detail}`);
   });
 
+  test("hides internal Agent error data from structured error details", () => {
+    const t = translatorFor("zh-CN");
+    const detail = 'driver: bad connection\nDBX_AGENT_ERROR_DATA:{"category":null,"agentSessionId":"session-1"}';
+    const error = {
+      version: 1,
+      code: "DBX-JDBC-9001",
+      messageKey: "backendErrors.jdbc.legacyFailure",
+      messageParams: {},
+      source: "jdbcAgentLegacy",
+      operationOutcome: "unknown",
+      detail,
+    } as const;
+
+    expect(translateBackendError(t, error)).toBe(`${t(error.messageKey)}\n\ndriver: bad connection`);
+  });
+
   test.each([
     ["array params", { messageParams: ["execute"] }],
     ["nested params", { messageParams: { stage: { name: "execute" } } }],
diff --git a/apps/desktop/src/i18n/backend-errors.ts b/apps/desktop/src/i18n/backend-errors.ts
index 334252020..9594f467b 100644
--- a/apps/desktop/src/i18n/backend-errors.ts
+++ b/apps/desktop/src/i18n/backend-errors.ts
@@ -1,4 +1,4 @@
-import { normalizeBackendError, type BackendError } from "@/lib/backend/errorUtils";
+import { normalizeBackendError, sanitizeBackendErrorMessage, type BackendError } from "@/lib/backend/errorUtils";
 
 /**
  * Minimal shape of a translate function, satisfied by both `useI18n().t` inside
@@ -115,15 +115,15 @@ const paramNames: Record<string, string | string[]> = {
 };
 
 function backendErrorMessage(error: unknown): string {
-  if (typeof error === "string") return error;
-  if (error && typeof error === "object" && "message" in error && typeof error.message === "string") return error.message;
-  return String(error);
+  if (typeof error === "string") return sanitizeBackendErrorMessage(error);
+  if (error && typeof error === "object" && "message" in error && typeof error.message === "string") return sanitizeBackendErrorMessage(error.message);
+  return sanitizeBackendErrorMessage(String(error));
 }
 
 function translateStructuredBackendError(t: BackendErrorTranslate, error: BackendError): string {
   const translated = t(error.messageKey, error.messageParams);
   const summary = translated !== error.messageKey ? translated : t("backendErrors.unknown");
-  const detail = error.detail?.trim();
+  const detail = error.detail ? sanitizeBackendErrorMessage(error.detail).trim() : undefined;
   return detail && detail !== summary ? `${summary}\n\n${detail}` : summary;
 }
 
diff --git a/apps/desktop/src/lib/backend/errorUtils.ts b/apps/desktop/src/lib/backend/errorUtils.ts
index 4a0e0a9ce..72ad60dbb 100644
--- a/apps/desktop/src/lib/backend/errorUtils.ts
+++ b/apps/desktop/src/lib/backend/errorUtils.ts
@@ -16,6 +16,23 @@ export interface BackendError {
   helpUrl?: string;
 }
 
+const AGENT_RPC_ERROR_DATA_MARKER = "\nDBX_AGENT_ERROR_DATA:";
+
+export function sanitizeBackendErrorMessage(message: string): string {
+  const markerIndex = message.lastIndexOf(AGENT_RPC_ERROR_DATA_MARKER);
+  if (markerIndex < 0) return message;
+
+  const rawData = message.slice(markerIndex + AGENT_RPC_ERROR_DATA_MARKER.length).trim();
+  try {
+    const data: unknown = JSON.parse(rawData);
+    if (!data || typeof data !== "object" || Array.isArray(data)) return message;
+  } catch {
+    return message;
+  }
+
+  return message.slice(0, markerIndex).trimEnd();
+}
+
 function isBackendError(value: unknown): value is BackendError {
   if (!value || typeof value !== "object") return false;
   const candidate = value as Record<string, unknown>;
@@ -56,8 +73,8 @@ export class BackendErrorException extends Error {
 
   constructor(error: unknown) {
     const backendError = normalizeRawBackendError(error);
-    const fallbackMessage = typeof error === "string" ? error : error instanceof Error ? error.message : "Backend request failed";
-    super(backendError?.detail || fallbackMessage);
+    const fallbackMessage = sanitizeBackendErrorMessage(typeof error === "string" ? error : error instanceof Error ? error.message : "Backend request failed");
+    super(backendError?.detail ? sanitizeBackendErrorMessage(backendError.detail) : fallbackMessage);
     this.name = "BackendErrorException";
     this.backendError = backendError ?? {
       version: 1,
@@ -99,14 +116,14 @@ function normalizeRawBackendError(error: unknown): BackendError | null {
  */
 export function formatError(e: unknown): string {
   const backendError = normalizeBackendError(e);
-  if (backendError?.detail) return backendError.detail;
+  if (backendError?.detail) return sanitizeBackendErrorMessage(backendError.detail);
 
   if (e instanceof Error) {
-    return e.message;
+    return sanitizeBackendErrorMessage(e.message);
   }
 
   if (typeof e === "string") {
-    return e;
+    return sanitizeBackendErrorMessage(e);
   }
 
   if (e === null || e === undefined) {
@@ -117,13 +134,13 @@ export function formatError(e: unknown): string {
   if (typeof e === "object" && "message" in e) {
     const message = (e as { message: unknown }).message;
     if (typeof message === "string") {
-      return message;
+      return sanitizeBackendErrorMessage(message);
     }
   }
 
   // Fallback: attempt to stringify
   try {
-    return String(e);
+    return sanitizeBackendErrorMessage(String(e));
   } catch {
     return "Unknown error occurred";
   }